BUTJ,RTIN No. 126 Storage and Transport of Fish Refrigerated Sea Water BY • In S. . ROACH, J. S. M. HARRISON and H. L. A. TARR Fisheries Research Board of Canada Technological Station, Vancouver 8, B.C. WITH APPENDICES BY w. A. MacCAUM d M. S. C Fisheries Research Board 0/ Canada Technological Unit, St. John's, Nd. a A. W. Z Fisheries Research Board 0/ Canada Technological Unit, London, Onto PUBLISHED BY THE FISHERIES RESEARCH BOARD OF CANADA UNDER THE CONTROL OF THE HONOURABLE THE MISTER OF FISHERI ES ��� � � · �r ! ·AA, 1961 15 cents �L I ��
Transcript
BUTJ,RTIN No. 126
Storage and Transport of Fish
Refrigerated Sea Water
BY
•
In
S. 1V. ROACH, J. S. M. HARRISON and H. L. A. TARR
Fisheries Research Board of Canada
Technological Station, Vancouver 8, B.C.
WITH APPENDICES BY
w. A. MacCALLUM and M. S. CHAN
Fisheries Research Board 0/ Canada
Technological Unit, St. John's, Njld.
and
A. W. LANTZ
Fisheries Research Board 0/ Canada
Technological Unit, London, Onto
PUBLISHED BY T H E FISHERIES RESEARCH BOARD OF CANADA UNDER THE CONTROL OF THE HONOURABLE THE MINISTER OF FISHERIES
�==����·�r!·'TA1VA, 1961
15 cents
�LI ______________________ ��
The hatchway to one of the refrigerated sea water tanks on a British Colu1l1bia combination and halibut long-liner. The crew has just completed a set for salmon ;ll1d the last
fish arc being put into the tanks for storing and transporting the vessel's catch.
BULLETIN No. 126
Storage and Transport of Fish Refrigerated Sea Water
BY
• In
S. W. ROACH, J. S. M. HARRISON and H. L. A. TARH
Fisheries Research Board of Canada Technological Station, VancOlwer 8, B.C.
WiTH APPENDICES BY
W. A. MacCALLUM and M. S. CHAN Fisheries Research Board of Canada
Technological Unit, St. John's, N/ld.
and
A. W. LANTZ Fisheries Research Board of Callacla
Technological Unit, Lonclon, Onto
PUBL ISHED BY T H E FISHERIES RESEAR CH
BOARD OF CANADA UNDER THE CONTROL OF
THE H ONOURABLE THE MINISTER OF FISHERIES
OTTAWA, 1961
D21G2-7---1
Editor:
W. E. RICKER
Fisheries Research Board of Canada
P .O. Drawer 100 Nanaimo , B . C., Canada
A ssociate Editor:
N. M. CARTER
Fisheries Research Board of Canada
Sir Charles Tupper Building
Ottawa, Ont., Canada
ROGER DUHAMEL, F,R.S,C. QUEEN'S PRINTER AND CONTROLLER OF STATIONElty
OTTAWA, 1961
Price: 75 cents. Cat. No. Fs 94-126
IV
BULLETINS OF THE FISHERIES RESEARCH BOARD OF CANADA are published from time to time to present popular and scientific information concerning fishes and some other aquatic animals ; their environment and the biology of their stocks ; means of capture ; and the handling, processing and uti l izing of fish and fishery products.
In addition , the Board publishes the following :
An ANNUAL REPORT of the work carried on under the direction of the Board.
The JOURNAL OF THE FI SHERIES RESEARCH BOARD OF CANADA, containing the results of scientific investigations.
ATLANTIC PROGRESS REPORTS, consisting of brief articles on investigations at the Atlantic stations of the Board .
PACIFIC PROGRESS REPORTS, consisting of brief articles on investigations at the Pacific stations of the Board .
The price of this Bulletin is 75 cents (Canadian funds , postpaid) . Orders should be addressed to the Queen's Printer , Ottawa, Canada. Remittance made payable to the Receiver General of Canada should accompany the order.
All publications of the Fisheries Research Board of Canada still in print are available for purchase from the Queen 's Printer. Bulletin :'\To . 1 1 0 is an i ndex and list of publications of the Board to the end of 1954 and is priced at 75 cents per copy postpaid.
For a listing of recent issues of the above publications see inside of back cover. These publ ications may be consulted at l ibraries of any of the Board's establishments and in many Canadian university and public libraries.
v 92162-7-2
FOREWORD
This Bulletin was prepared as a result of a request by the Fisheries Research Board of Canada Western Advisory Committee and submitted for publication in November, 1 9 59 . I t was intended to be a concise review publication which would set out the known uses of this somewhat novel, though not entirely new, method of holding chilled fish. Publ ication was delayed since it was felt in some quarters that the Bulletin might be of greater value if data regarding holding of Canada 's Atlantic Ocean and inland lake fish were included . This has resulted in the inclusion of two Appendices , one of which describes in extenso the results of experiments conducted at this Board 's Technological Station, Halifax .
No claim is made that this method is infall ible , and in fact the dangers attending improper appl ications are stressed frequently. However , for certain fisheries this procedure has proved very valuable , especially for the holding and transportation of Pacific salmon. Indeed , extensive experimental and industrial experience on the west coast with salmon and ground fish has repeatedly shown that it is practical to maintain a temperature of 30° F with ful l -strength sea water and without significant freezing of the fish. In east coast work a temperature of 32° F was used since at 30° F the fish appeared to freeze and the salt content of the sea water used had to be increased to 5 % to maintain this lower temperature. No satisfactory explanation is offered for this apparent discrepancy. Indeed , as reported by U.S. Bureau of Commercial Fisheries investigators ( 12th Annual M eeting of Pacific Fisheries Technologists , Bell ingham , Wash . , March 1 9-22, 1 9 6 1 ) , experiments carried out in the Boston area with whiting indicate that these fish stored well in refrigerated sea water at 30° F, and apparently without freezing.
In conclusion, it cannot be emphasized too strongly that refrigerated sea-water holding of fish in any fishery must be carefully assessed before largescale applications are effected . Factors such as salt penetration and control of bacterial contamination must be most carefully studied over given time intervals , and standards such as time l imits for holding carefully adhered to. If this is done , then it is quite possible that this general method may not only simplify handling, but will improve quality of fish landed in many areas .
ApPENDIX I . Experiments on the storage o f Canadian Atlantic Coast cod in refrigerated sea water . . . . . . . . . . . . . . . . . . . . . . . . 41
ApPENDIX 11. Chilled water for the preservation of freshwater fish . . . . 59
IX
I NTRODUCTION
As mentioned in a previous brief review of this subject (Tarr and Harrison, 1 95 7 ), it is impossible to state with certainty when fish were first preserved transiently by storing them in refrigerated sea water (RSW) . In 1 920 a French patent was assigned to Le Danois (1920) which covered holding fish on boats at _4° C (24'8° F) in sea water or in brine, a treatment which would obviously freeze fish if carried out for any extended period . Undoubtedly the first significant contribution was made between 1928 and 1 930 by H untsman ( 1 93 1 ) , who showed that fish could be held i n a tank of circulating sea water chilled by large blocks of ice, and suggested that mechanical refrigeration could replace ice in such a system . He indicated the potential value of such a storage method if it were appl ied to fishing vessels, and demonstrated its feasibility in experimental storage of fish on shore. Chemical and bacteriological studies carried out about the same time by Hess ( 1 933) showed that, at temperatures which were j ust above the "freezing point" of fish muscle, namely 30° F (-l· l° C), fish flesh would keep about twice as well as that held at 36° F (+ 2 . 2 ° C). These early tests aroused no real interest and for about a decade and a half no further work was carried out on the subject .
About 1944 interest was renewed, particularly concerning the possibility of applying the method for storing rather perishable California sardines for canning. The literature from 1 944 to 1 95 7 has been reviewed (Osterhaugh, 1 95 7 ) . I n California, where sardines were still abundant about 1 944, there was a need for quite rapid cooling of large quantities of these fish for canning. The use of three generally different methods of cooling the brine to be used for rapid chilling and holding these fish for canning, and the necessity for observing sanitary precautions, was pointed out by Lang et al. ( 1 945) . The performance of certain commercial installations and many other desirable features of these was outlined by Davis et al. ( 1 944, 1 945 ) . About the same time Sigurdsson ( 1 945) demonstrated that Atlantic herring intended for canning could be stored in refrigerated brine. I n the U .S .S .R . Konokotin ( 1 949) found that sprats intended for smoking could be cooled rapidly and held for 3 6 hours in rigor mortis in brines chilled to 28 ° or 30° F , and that this method of storage was preferable to that of holding the fish in ice . A study begun in 1 953 on the effects of prechilling Yugoslav sardines in shore tanks of non-agitated RSW constantly chil led to 28 ° F
(-2 . 2° C), as compared with the effects of three other methods of prechilling prior to cold storage before canning, was reported by MacCallum et al. ( 1 956) .
I t is noteworthy that all the foregoing work was concerned with fish held in shore tanks . The possibil ity of using this method for storing fish on vessels, as suggested by H untsman, was again pointed out in 1 947 when it was stated that "clean sea water (or a 3 % salt brine) cooled with crushed ice or by other means will have a temperature of about 2 9° F and might be of value in fish wells similar to the refrigerated brine wells used in tuna boats" (Tarr, 1 947) .
It was not until 1955 that a comparatively large installation was studied . Engineering and other information gained from these early trials, and from studies carried out elsewhere , will be described below. Farber ( 1 955 ) indicated the desirabil ity of chilling tuna and sardines in RSW at 29 to 30° F for a day before freezing them in stronger brines at lower temperatures, thus ensuring a preliminary washing of the fish .
In 1952 the results of experiments in which shrimp were transported in RSW on a fishing vessel were reported by Higman and Idyl l . This work will be described later. In 1952 this Vancouver Technological Station of the Fisheries Research Board of Canada commenced its program on storage and transport of fish in RSW, early work being confined to experimental installations on small fishing boats (Fisheries Research Board Annual Report, 1 953 ; Lantz , 1 953 ; Roach and Harrison, 1 954; Harrison and Roach , 1 954) .
Before proceeding to an active discussion of the subj ect it is important to mention several reasons why holding fish in RSW as an alternative to the more usual procedure of storing them in ice offers considerable appeal to many fishermen and fish processors. Fish held in RSW have a buoyancy almost equal to their weight and hence do not tend to crush . Even after prolonged storage they are usually firmer and are not ice pitted . Unloading fish from RSW may sometimes present fewer problems than are encountered in removing them from ice , but in general there do not seem to be too many advantages. In some of the larger installations it has been possible to employ a sluicing method to facilitate unloading (see section on salmon packers, page 24) . Since the density of fish flesh increases slightly as its temperature decreases , fish caught in comparatively warm waters then placed in RSW do not settle into a compact mass until thor
oughly chilled . Because of this, maximum tank loading may be safely obtained
since there is no danger of trapping a comparatively warm mass of fish in one
part of the tank. I t is important to emphasize that the fish storage capacity of medium or large vessels using RSW tanks is approximately equal to that of
similar vessels using ice in uninsulated holds.
Fish held in RSW should be stored at about 30° F (- 1 · 1 ° C) , for at temperatures below this ice crystals form in the muscle . Even under ideal conditions
fish stored in ordinary melting ice will not attain temperatures significantly below 32 ° F (0° C) . Indeed , the conditions employed in icing fish aboard many
commercial vessels are such that the fish often exceed 35 ° F (+ 1 . 7 ° C) . I t is ob
vious that fish , unless covered by a water-vapour-impermeable material , cannot be
stored in air at 30° F (-1 · 1 ° C ) without surface drying, if the atmosphere is not
saturated with respect to water vapour. It is almost impossible to accomplish
this last-named condition in practice , for cooling surfaces automatically remove
water from the atmosphere and therefore methods of storing fish at about this
temperature have either employed ices , or solutions, containing various solutes
which lower the freezing point. Probably one of the greatest values of ice l ies in
its ability to bathe surfaces of fish with a slow stream of clean water and thus help to remove bacteria and their undesirable metabolism products (Tarr, 1 95 7) .
2
I t is therefore obvious that the use of mechanical refrigeration as an adj unct to ice for storing fish must be carefully controlled , for if the temperature should fall below 32° F (0° C) the ice wil l no longer melt and the usually highly contaminated slime will not be washed from the fish . The only useful function performed by mechanical refrigeration in this instance is to reduce excessive ice loss due to heat leakage, and in most instances such losses can be avoided more economical ly by use of adequate insulation .
Another important consideration in the use of RS\i\f is the elimination of the often tedious and sometimes difficult task of icing fish thoroughly at sea . Certain other problems often associated with use of ice are also eliminated . Thus the difficulty of predicting exactly the amount of ice required for a given trip , the seasonal scarcities which may result in elevated prices for ice , and the shortages occasioned at sea by forced delays or high air and sea-water temperatures , are no longer of concern to the fisherman. Finally by use of RSW fish are cooled rapidly. In fact , in a properly designed RSW system , heat is removed from the fish more rapidly than it can be transmitted through the fish flesh itself . This is demonstrated by the immediate rise in temperature that occurs in chilled sea water in tanks which are loaded with comparatively warm fish. Thus , when the sea water is rapidly cooled to , say , 30° F (-1·1 °C) and the refrigeration is shut off, the sea water commences to increase in temperature at a rate which can only be accounted for by the heating action of the fish.
It mnst be emphasized that there are certain l imitations to use of RSW, and some of these will be discussed later . Thus, among the numerous installations which have been made on vessels in the Pacific northwestern area in the past few years , there have been some which have failed due to a lack of understanding of the basic requirements for a satisfactory system . The operators of such systems must have a reasonable amount of training. The system itself must be properly engineered and capable of meeting design specifications which should include ultimate holding temperatures , " pull-down " time, and maximum allowable temperature rise during the off-cycle . Above all , RSW installations must be readily cleanable and not contain any focal points of bacterial infection .
From the point of view of its use in holding fish , sea water may be regarded as a solution of numerous inorganic salts . In general , the ratios and amounts of these dissolved salts in undiluted sea water are fairly uniform , and for the purposes of this description the content of total dissolved salts (salinity) may be regarded as 3 · 5 % (35 parts per thousand or 35% 0), Undiluted sea water ( i .e . sea water not too close to the surface or to mouths of rivers) has about the following average principal composition in parts of inorganic constituents per thousand parts of the water (Lyman and Fleming, 1 940):
Sodium chloride
Magnesium chloride
Sodium sulphate
Calcium chloride
23 · 476
4 · 98 1
Potassium chloride
Sodium bicarbonate 3 · 9 1 7 Potassium bromide
1 . 1 02 Boric acid
Strontium chloride 0 · 024 .
3
0 · 664
0 · 1 92
0 · 096
(l · 0 26
Dilution, particularly by river waters, may cause very significant reductions and variations in salinities. Thus, in the Baltic Sea and near the mouth of large river systems such as the Skeena and Fraser in British Columbia, the salinity may be as low as a few parts per thousand . On the other hand, high temperatures and strong winds may raise the salinity significantly. Thus, the water of the Red Sea has a salinity of about 400/00 , Where at all possible fishermen should try to obtain clean deep sea water of roughly known salinity. It is impossible to maintain a temperature of 300 F unless the sea water used has a salinity of at least 200 /0 0 ,
Figure 1 shows the specific gravities and freezing points of sea water as functions of salinity. The salinity of a given sample of sea water may be determined readily by means of a hydrometer calibrated to the range indicated in the Figure . I t will be seen that the freezing point of sea water is lowered one degree Fahrenheit for each increase of 100/00 in salinity. Another important characteristic of sea water is that whereas pure water has its maximum density at 39 . 2 0 F (40 C) , the temperature of maximum density for sea water decreases with increasing salinity, as shown in Fig 1 .
FIG. 1 . Specific gravity and freezing point of sea water as functions of salinity. Distilled water at 39.2° F (4° C)
= 1 . 000.
4
ENGINEERI NG
GENERAL I NFORMATION
The engineering and other aspects of actual freezing fish at sea are being actively studied by maritime countries. Though superficially the practice of storing fish in RSW on vessels might appear to pose rather similar problems to those arising in freezing them, the actual requirements in terms of equipment are very different . In RSW installations the fish are chilled and stored in the same medium (sea water) and the equipment and tanks are designed for this exclusive use. To freeze at sea, provision must also be made for refrigerated storage of the frozen fish. Further, the machinery required for RS\V installations
is simpler and less expensive because the total heat which must be removed in chilling fish to 30° F (-1 ·1 ° C) is much less than to freeze them , and need not be removed as rapidly. As an example , cooling a 1 0-lb fish from 50° F ( 1 0° C) to 30 ° F (-1·1 ° C) requires removal of only 1 60 BTU, while 1 320 BTU are required to chill and freeze such a fish so that its final temperature is 0° F (-1 8° C) . The heat to be removed in freezing this fish is thus seen to be of the order of eight times that which is removed in cool ing it to 30° F. From this consideration alone it can readily be seen that the refrigeration equipment and power requirements for freezing fish at sea will be much larger than for chilling with RSW.
Although fish may be stored in RSW in a simple tank using only ice , sea water and a circulating device , this arrangement creates several problems. Thus, though it is a simple matter to calculate the ice requirement of such a system, it is mandatory that the ice melt rapidly enough to maintain a temperature of 30° F (-1,1 ° C) . Circulation must be sufficiently rapid to ensure that no temperature stratification occurs , since the ice tends to float on the surface , and specific gravity differences between fresh water near the melting ice and the sea water tend to increase this stratification. For comparatively long periods of storage , addition of salt may be necessary to maintain the salinity as it becomes lowered by dilution from the melting ice . It is obvious that mechanical installations have many advantages both on vessels and on shore . However , such installations involve a knowledge of refrigeration theory , power supplies , compressors , insulation, corrosion and even devices for unloading fish.
REFRIGERATION THEORY
Figure 2 il lustrates a typical refrigeration system. Since it is necessary to
know the performance of refrigeration compressors under various conditions of temperature and load, the performance curves for a 5 -hp Freon- 1 2 compres
sor of a type often used in RSW installations are shown in Fig. 3. These curves
show the BTU output and horsepower requirements for two different head
pressures and a range of suction pressures. A study of these curves reveals the
fol lowing information, which applies to any RSW system.
5 92162-7-3!
I n a properly designed and functioning RSW system suction gas temperature will be approximately 40° F when the tank is at 60° F, fal l ing to about 20° F when the water is cooled to approximately 30° F . A point to be noted is that in this suction temperature range ( i .e . , 40 to 20° F) , there is l ittle change in the brake horsepower . Thus there is no need to provide protective devices against overload of the motor or other driving device during " pull-down " as is usual ly
required in refrigeration systems . Another point to be noted is that the capacity
of the system greatly decreases as the suction temperature becomes lower.
For this reason the system should be designed with adequate heat exchanger surface to avoid unduly low suction temperatures and associated loss of capacity.
A third point is that high discharge temperatures increase the power required and decrease capacity. H igh discharge temperatures are caused either by warmer condensing water or by high suction temperatures . Since these conditions may be
unavoidable, provision must be made for increasing the condensing rate to meet
these demands . This means that the condenser must be made large enough to
compensate for both high cooling water and tank water temperatures . This
approach differs from that generally used in designing refrigeration systems
because it allows the greatest possible refrigeration output during the pull -down period when high capacity is most needed . Unfortunately , it requires control
devices , either manual or automatic , to decrease the condensing rate when lower temperatures are reached . Such controls either by-pass gas around the condenser
or restrict or by-pass cooling water .
LIQUID LINE
EXPANSION VALVE
EVAPORATOR
CONDENSER
FIG. 2. Schematic drawing of a simple refrigerated sea water refrigeration system.
6
TANKS
90
a:: so ::> ° :x: 0:: III CL ::> 70 I-al ° o Q x 60 >-I-(3 ct <[ u
50 C) z � 0:: III C) E 40 III a::
30
_CAPACITY AT 900 SAT. DISCH. TEMP. F.
S.H.P. AT 1050 SAT. DIS CH. TEMP. F.
CAPACITY AT 1050 S AT. DISCH. TEMP. ( 20L-____________________________________ �
50 40 30 20 10 o SATURATED S UCTION VAPOR TEMPERATURE F.
5
40:: III � Q. III (fl 0::
3° :x:
2
III � 0:: al
FIG. 3. Performance curves for a 5-hp Freon- 1 2 compressor.
The basic requirements for tanks used for RS\� are that they be watertight ,
easily cleaned , corrosion-resistant and that they do not absorb moisture. In
Canada, such tanks on vessels of over 1 5 tons gross weight must comply with the
regulations of the Canada Department of Transport (Anon . , 1 9 56a) . These
include specifications for wall thickness and bracing, height and cross-sectional
area of tank filling trunks and for the elimination of large free water surface in
the tanks during pitching or rolling of the vessels (see Frontispiece). The size
and shape of tanks will depend on the type of application , and for a rough guide
their storage capacity in terms of fish may be taken as 50 Ib of fish per cubic
foot of tank volume. It has been found that even when 80% by weight of the
sea water is displaced by fish in a loaded tank, adequate passage still remains
between the fish for circulating sea water for cool ing. I t is much easier to install
tanks in a new vessel dnring construction than to install them in an older one ,
and this also permits a wider choice of materials.
7
From a study of various tank installations on fishing vessels two general layouts have emerged which best satisfy the requirements for safety, convenience and carrying capacity. The first of these is shown in Fig. 4 and is suitable for small vessels such as trollers . This arrangement was used on the Ruth G II (Roach and Harrison, 1958 ) and has many advantages . These include ( 1 ) the least possible change in the hold of the vessel due to the location of the tanks in the most efficient load-carrying part of the hull, ( 2 ) ample space in the remainder of the hold for conventional icing of surplus fish, (3 ) the shaft and bearings are accessible, and (4) the centre tank can be designed for removal of the boat's engine. The other layout, shown in Fig. 5, was used on the Silver Viking II (Anon . , 1958a, 1 958e) and has proven most satisfactory. This layout provides in addition to the RSW tanks, a large central hold which gives access to propeller shaft and bearings, provides additional space for packing herring and for icing fish after the tanks are filled, and also permits easy unloading of salmon and halibut.
MAIN HOLD
TANK
HATCH TANK
TANK
FIG. 4. Plan of M. V. Ruth G II.
TANK
TANK
ENGINE
ROOM
FIG. 5. Plan of M . V. Silver Viking II.
STRUCTURAL REQUIREMENTS
When considering structural requirements for RSW tanks the chief cause
for concern is in the design of vertical bulkheads . Other panels are usually
adequately supported by the hull of the vessel. The Canada Board of Steamship Inspection regulations (Anon . , 1 9 56a) cover the design of steel bulkheads and are simple and appropriate for applying to tanks . These call for Is-inch steel
plate having a maximum of 6 square feet of unsupported surface between stiffeners.
The m inimum requirement for stiffeners is 2 X 2 X i-inch angle irons, toe welded to the tank plate . Aluminum plate should be increased in thickness over steel to offset the former's lower ultimate strength and modulus of elasticity.
8
Thus, 2t X 2 X i-inch angle aluminum stiffeners for i-inch aluminum plate will be comparable to the above figures for steel . Plywood bulkheads must be s imilarly stiffened. The following are the minimum requirements for t-inch fir plywood tank bulkheads :
Tank depth
Under 3 feet ...... . ............... .
Vertical stiffeners
None
Between 3 and 4 feet. . . . . . . . . . . . . . .. 2 by 3-inch fir
2 by 4-inch fir
Between 4 and 5 feet. . . . . . . . . . . . . .. 2 by 4-inch fir
Between 5 and 6 feet. . . . . . . . . . . . . .. 2 by 6-inch fir
Centers
1 2-inch
24-inch
1 2-inch
1 6-inch
Critical attention should be paid to the j oints of plywood tanks . The thrust of water on the bottom horizontal j oint of a tank bulkhead is 333 lb per l ineal foot of j oint for a 4-foot-deep tank and 750 lb per foot for a 6-foot-deep tank. Bolted angle iron corners are recommended.
MATERIALS
The above-mentioned basic requirements permit a wide selection in tanklining materials. Aluminum, steel, plywood and plastics are used and many other materials appear suitable. However, problems are presented in the use of an y lining material .
Certain aluminum alloys are excellent for tank construction . They have high resistance to sea-water corrosion, are readily cleaned, and are light in weight . These alloys contain magnesium and magnesium silicide . Alcan B54S and 5 7S are two such alloys. I t should be noted that most other aluminum alloys have low resistance to sea-water corrosion. Unpainted aluminum tanks were used on the troller Phantom II (Harrison and Roach, 1 954) and the salmon packer J.R.D. (Harrison and Roach, 1955 ) and have remained virtually unaffected by corrosion after several seasons of use . Aluminum is an expensive material when compared with steel since its l ightness is more than offset by its lower rigidity. Aluminum and its alloys should not be used in contact with other metals in the presence of sea water due to its position in the galvanic series, since with the common metals such as copper, brass or steel i t will corrode rapidly. Thus all tank fittings must be of aluminum or non-metall ic material . Welding of aluminum is usually done by using an inert gas-shielded arc process which is designed for shop work rather than for use in the field . Thus welding repairs or modifications to aluminum tanks cannot be done conveniently on boats or in outlying plants . Table I gives the physical and mechanical properties of steel and of some of the aluminum alloys which may be used in tank construction . Steel has also proven a satisfactory material for RSW tanks, the chief problem in its use being prevention of corrosion . One solution to this corrosion problem is the use of sacrificial anodes of magnesium or zinc to give galvanic cathodic protection to the bare metal . The services of a specialist in this field will be required for large
9
tanks . A more common solution is to protect the surfaces by a suitable coating. The durability of this protective coating depends a great deal on the surface preparation of the metal . This should consist of sandblasting fol lowed by the immediate appl ication of a suitable primer. Among the coatings which have proven satisfactory are zinc galvanizing (Anon . , 1 9 5 7a) , epoxy resins (Harrison and Roach , 1 95 7 ) , and thiocol rubber base coatings . A low-cost treatment of steel which has been satisfactory consists of painting the untreated steel with a non-toxic bituminous paint (Roach and Harrison , 1 958) , which should be frequently renewed since it may be applied even to damp surfaces.
TABLE 1. Some physical and mechanical properties of mild steel and three aluminum alloys.
Thermal conductivity, Young's Yield Ultimate
Density, BTU /( hr)(sq ft ) modulus, strength, strength , Ib/ft3 ( OF per ft ) (psi X 1 0 6) psi psi
Plywood is often chosen for tank linings because it is relatively inexpensive and easily worked . Here the problem is the selection of a suitable coating to prevent leaks and water absorption . Plywood should be kept dry to prevent attack by moulds (dry rot) , which means that it should be completely protected from absorbing water . Water absorbed from the inside may also create a serious sanitary problem by carrying fish-spoiling bacteria into the wood itself . For this reason it is desirable to use resin-faced plywood which is impervious to water. Glass-reinforced plastic and " Celastic" (Anon . , 1 959a) l inings for plywood tanks have been successful and are equally waterproof.
Plastic reinforced with glass fibres as mentioned above has many attractive features favouring its use as a tank-lining material . I t is non-toxic and noncontaminating, will not absorb water, can be finished to a very smooth surface and , for smaller tanks , can be applied by the owner. It was used to line the tanks of the halibut fishing vessel Silver Viking II (Harrison, 1 959) . In this case the lining was applied over Styrofoam (a polystyrene "foam" preparation) insulation , which has the disadvantage of being vulnerable to attack from solvents such as are normally used in the glass fibres and plastic application . In an attempt to overcome this problem the Styrofoam was coated with resorcinol resin prior to appl ication of the plastic . However, this did not succeed and the sea water penetrated between and behind the insulation . To correct these faults the linings and insulation were removed and cork insulation was installed . The tanks were then l ined with plywood and covered with a heavy glass fibre and plastic coating. These repairs were very effective and 11 0 further leaks have developed in service .
1 0
<:0 "" .....
� I "'"
....... .......
I nsulating material
Cork
Foamglas (cellular glass)
Styrofoam (polystyrene plastic)
Fir plywood
Rubatex (expanded synthetic rubber)
Dylite (polystyrene plastic)
TABLE I I . Some physical properties of certain materials which may be used in insulating RSW tanks.
K factor thermal con- Linear thermal Compressive
ductivity, coef. of ex- yield Density, BTU/ft2/ pansion, strength, JVIoisture
Ib/ft3 hr/oF lin in/in;oF psi absorption Adhesives Remarks
1 2 0 . 30 Absorbs water Hot-melt asphalt Combustible or cold-setting type
Concrete and asphalt-portland cement plaster have also been used as tank-l ining materials . This type of lining is inexpensive , can be applied easily and appears particularly suitable for steel-hulled vessels . The forward tanks on the Snow Mist (Anon . , 1 9 5 7a) are concrete lined and considered satisfactory by the owners . With this installation a suitable insulation was bonded to the steel hull and covered with a concrete plaster coating. For wooden vessels a more flexible plaster is necessary , incorporating flexible materials such as asphalt (Roach, 1958) . The chief problem with this type of lining is in obtaining a smooth , leak-proof, non-absorbing finish .
INSULATION
The insulation of RSW tanks is often difficult , particularly when they are being installed on a vessel . The greatest problem is installing a completely vapour-proof barrier around the insulation . This , of course , is vital , since the insulating value is not maintained if the insulation becomes waterlogged. Although asphalt-coated cork is frequently used for insulating RSvV tanks , there are other , more waterproof , types of insulating materials which are preferable . Table I I gives the properties of some of the insulating materials which may be used. As may be noted from this Table , adhesives for applying the insulation must be carefully selected . These are classified into three main categories: ( 1 ) those which set by evaporation of a l iquid (drying type); ( 2 ) those which set by a chemical process (cold-setting type); and (3) the hot-melt type which are general ly asphalt- or wax-based materials . The choice of an adhesive [or any particular bonding application depends on numerous factors including: initial bond; strength of bond; bond to the material of the insulated area; vapour porosity of the material and of the area to be bonded; method of application (brushing, spraying, trowelling, etc . ) ; toxicity; fire hazard; cost; also water , chemical and heat resistance.
COMPRESSORS
In selecting compressors for RSW service there are certain important factors to consider . Among these are reliability, compactness and l ightness . Fortunately, Freon- 1 2 systems and components are very reliable for they are designed to operate with l ittle attention or maintenance for periods of years. Both compactness and l ightness are now available in modern high-speed compressors and at l ittle sacrifice in efficiency or reliability. Hermetic motor compressors are desirable when electric power is available as they are more compact and eliminate the possibility of leakage through the shaft gland.
When selecting compressors for RSW service it is important to consider the number of cylinders if hydraulic or electric drive is to be used . With either of these drives the allowable starting torque may be l imited as is shown in the following equation (Hirsch , 1 954) :
(P2 - PI) V
Ts = -----24
12
where
Ts starting torque, Ib-ft ,
P2 discharge pressure , pounds per square inch , absolute ,
Pi suction pressure , pounds per square inch, absolute ,
V volume of cyl inder, cubic inches . (Use only one volume for a 2- or 4-cylinder compressor . )
Since a 2 -cylinder compressor has a cyl inder volume twice that of a 4-cyI:nder compressor of the same output at the same speed , its starting torque is also twice that of the 4-cylinder compressor. This is because of the crank arrangement which causes only one cylinder at a time to require maximum torque in either a 2- or 4-cylinder compressor. From this equation it can also be seen that a cylinder by-pass line from the suction to the discharge line can reduce (Pz - Pi) to zero and hence reduce the starting torque to zero . The use of a manual valve in this by-pass l ine can be of great value in eliminating difficult starting.
vVhen selecting compressors which are to be driven mechanically from the boat's main engine , the speed range of the engine must be carefully considered . All compressors have a lower speed l imit below which lubrication will fail , and since compressor capacity varies directly with speed , the other components of the system must be able to compensate for variations in capacity. The new automotive-type compressors which are widely used in truck refrigeration are well suited for use on fishing vessels where they can be driven directly from the main engine, for they have a speed range of from 5 00 to 4 ,000 r .p.111. through which they can run continuously without lubrication problems.
DRIVES
In the selection of a drive for the compressors and pumps in RSW installations a decision must be made on the basis of cost, convenience and reliability. The alternatives are electric motor , hydraulic motor or mechanical drive from either the main engine or auxiliary engine . An electric motor is the logical choice for large vessels and shore installations where electric power is readily available . I t also proved satisfactory on the combination fishing vessel Silver Viking (Harrison and Roach , 1 95 7 ) . On this vessel electric power was supplied by two d iesel-driven alternating-current generators. These generators were the 1 20-2 08-volt type which supply single-phase 1 20-volt a-c current for the small motors and ship lighting and 208-volt 3 -phase power for the larger motors. On the Silver Viking II (Anon., 1958e) the 1 2 0-208-volt 3-phase a-c system was again used . This vessel has two generators , either of which can handle the complete electrical load . One of these is driven by the auxil iary diesel engine while the other is driven from the front end of the main engine and is used only at cruising speed . Most of the large fish packers and barges equipped with RSW systems for the Alaska salmon fisheries use diesel-powered generators.
Hydraulic drives for this equipment have certain advantages : the compressor can be placed in the most advantageous location; stopping and starting the
1 3 92162-7-4!
compressor are simplified ; constant speeds are obtainable; and the equipment
can be consolidated with other hydraulic equipment on the vessel . However,
the latter two advantages are usually obtained at a sacrifice of efficiency. This
low efficiency is not caused by the hydraulic pump or motor, which have high efficiencies, but by the fixed-pressure system which is usually employed to obtain
these advantages. Fixed-pressure systems are not satisfactory for driving refri
geration compressors which require varying starting and running torques. Low
efficiency should be avoided in RS\V systems, not only for fuel economy but
also because it results in loss of needed main-engine power or in the oversizing of an auxiliary engine . In other vessel auxiliaries such as winches or gurdies low
efficiency can be tolerated since the duration of operation is short.
Mechanical drives have certain distinct advantages and are particularly desirable when the power source is a constant-speed auxiliary engine used to
run one compressor and two or more small pumps. The salmon tender J.R.D.
uses this system (Harrison and Roach, 1955 ) . Many installations on smaller
vessels such as trol lers utilize V-belt drives from the front end of the main
engine but the problem of speed variation between trolling and cruising speeds
is difficult to solve . The addition of clutches and speed-changing devices is a solution but the cost may become excessive so that an auxiliary engine is often
used to power the refrigerated sea-water equipment used. The automotive-type
refrigeration compressor will operate over a large speed range and may be driven
from the main engine since the loss of capacity at trolling speeds is offset by the long running periods . Rotary-type pumps must be used for circulation since
their output at the various speeds roughly parallels that of the compressor.
CONDENSERS
In selecting condensers for a RSW system the chief consideration is resist
ance to corrosion . Cupro-nickel alloys are most suitable but stainless steel,
copper and brass are used . Commercial marine cleanable double-tube condensers
are generally used with the sea-water coolant supplied by a small pump which
must be sea-water resistant, constant speed and self priming. On smaller vessels using 2-hp or less compressor rating it is practical to use keel coolers of copper tubing attached to the hul l . The outside tube surface area of these should be
about 3 square feet per horsepower. In practice i t has been found necessary to
provide some means of temperature control on the condensers due to the variations in sea-water temperature . These temperatures could vary between 300 F
(_ 1 0 C) in the month of April in the Bering Sea to over 800 F ( 2 7 0 C) in tropical
zones . Thermostatic control of the cooling water supply, or condenser by
passing, is recommended in order to maintain suitable refrigerant head pressures .
As mentioned previously, high head pressures are undesirable in that they reduce
capacity. Low head pressures are also undesirable in that they cause malfunction
ing of the thermostatic expansion valve due to insufficient differential between
head and back pressures,
14
EVAPORATORS
At the Vancouver Station of the Fisheries Research Board of Canada several types of evaporators were studied and numerous laboratory tests conducted to produce what appears to be the most efficient type. In the first tests a coil to provide hold-over refrigeration in the form of ice on the outside of the coil to offset overnight heat leakage was designed. This system worked well on small installations where it was possible to provide overnight circulation by means of a small electric pump driven by the engine starting batteries (Roach and Harrison , 1 954) . In subsequent tests on a fish packer (Harrison and Roach, 1955 ) coils of this type were used and these were placed in the tanks behind a large baffle which served to keep the fish away from the coil surface. The three banks of coils (one per tank) were connected in parallel so that one or more could be operated at any time and each had its own circulating pump. The principle of "hold-over ice build-up " was again used. This system worked very well except that it was felt that the time required to precool the RSW in the tanks was too long. To achieve more rapid cooling an auxiliary chiller was designed to make use of all the available refrigeration to cool the sea water from its comparatively high temperature. This chiller (Harrison and Roach , 1 9 5 7 ) was designed with a close tube spacing permitting high water velocity and hence a high heat transfer from the tubes. Two of these chillers were installed , one on the
vessel J.R.D. and one on the Silver Viking. They have exceeded expectations,
for they are able not only to cool the sea water rapidly at the higher temperatures,
b ut continue to operate efficiently until the RSW temperature reaches the freezing point of the sea water, and do not ice up as long as the salinity of the sea water is such that its freezing point is only slightly lower than that of the fish flesh (about 29 . 5 ° F). This shell -and-tube chiller is of the U-tube type with refrigerant connections at one end so that the entire tube bundle may be removed from the shell. It is a non-flooded or dry-expansion cooler, with a thermal expansion valve for control of the Freon- 1 2 refrigerant. I ts advantages include a small Freon charge , a positive feed which assures oil return , and protection against burst tubes since it does not readily freeze. The success of such chil lers has greatly influenced later installations of RSW equipment. They are so efficient that they can be relied on entirely for cooling without employing tank coils. Their use greatly simplifies the installation and maintenance of RSW systems and provides greater flexibility and safety. The specifications for the design of chillers for 2 - to 7t-hp units are as follows:
Tubing:
Type K copper water tubing is used and after 3 years service there have so far been no corrosion problems.
Spacing The minimum spacing recommended is t inch , since t inch is the accepted spacing in dry-expansion chillers for clean water.
Size A wall thickness of 0 . 049 or 0 . 065 inch has been chosen to give maximum protection against corrosion .
1 5
Dimensions: Outside Wall Length per ft'
diameter thickness i nside wall (inch) (inch) area (feet)
0 . 625 0 .049 7 .3
0 . 8 7 5 0 . 065 5 . 1 3
Data for a lO-foot chiller , enclosed in a 6-inch pipe:
Outside Total inside Ratio of inside diameter No. of surface of surface to shell
(inch) tubes bundle (ft') volume (ft'/ft3)
0 . 625 24 33 1 6 . 7
0 . 8 7 5 1 8 3 5 1 7 . 8
This ratio of inside surface to shell volume should be kept as high as possible for
best results. Tests have shown that if suitable circulating pumps are used the
limiting factor for heat transfer in these chil lers is the film transfer coefficient
on the Freon side.
Outer casing
Baffies
Either polyethylene or Kralastic plastic pIpe IS preferred
and 2 - , 3 - , 4- and 6-inch nominal sizes have been used. Kralastic
pipe has the advantages of being rigid and having end fittings
available which can be plastic-welded in place. Polyethylene
pipe is less expensive but end fittings must be fabricated and
held in place by hose clamps. These plastic shells have three
distinct advantages over metal ones. They are light , will not
corrode or promote corrosion and are sufficiently elastic to
prevent rupture by freeze-up.
These are of copper , brass or plastic. Spacing these at one-shell
diameter interval gives good results.
Refrigeration factors
The recommended pumping rate for water is from 60 to 1 00 feet
per minute of fluid velocity across the tubes . The heat transfer
coefficient is 1 00 BTU /ft. 2;o F /hr. The recommended refri
gerant circuit lengths are 40 lineal feet per TX valve feed for
i-inch tube and 7 0 feet per TX valve feed for i-inch tube . Tubing
length per HP circuit averages 30 lineal feet of i-inch tube and
40 lineal feet of i-inch tube per horsepower. The split between
suction temperature and water temperature should be 1 0 degrees
Fahrenheit when water temperature approaches 30° F. Com
pressors will produce approximately 1 0 , 000 BTU /hp/hr.
1 6
....... -r
o
o
o 0'
o o
BAFFLE EDGES
�� I" CC RETURN BENDS
F- FEED S- SUCTION
1/4" BRASS 4-S0LVENT WELDED FLANGE
SOLVENT ./ WELDED/ REDUCER
FIG. 6. Schematic drawing of a 24 -tube chiller.
i
Figures 6 and 7 show the connections for chillers of 24 and 18 tubes and
illustrate schematically a 24-tube chiller.
FRONT END CONNECTIONS BAFFLE EDGES
USE 7/8·0.0. COPPER RETURN
BENDS FO R 2YaH CENTRES.
BACK END CONNECTIONS
FIG. 7. End connections for an 1 8-tube chiller.
CIRCULATING PUMPS
I n selecting pumps for RSW circulation , among the important factors to
consider are the hydraulic head , capacity , effect of speed variation and resistance
to corrosion. The head in most installations will be low if care has been taken
in selecting pipe sizes . Thus it is possible to use a low-head pump to circulate
a large volume of brine , using very l ittle power. For example , the chiller centrif
ugal circulating pump on the Silver Viking (Harrison and Roach , 1 9 5 7 ) was
of bronze with 2-inch discharge drawing 2 B H P at 2 , 000 rpm, the flow being
approximately 200 gal/min . This was adequate for chilling and holding over
1 00 ,000 lb of fish in six separate tanks. Speed variation can be a problem on
smaller vessels such as trollers where the pump is driven from the main engine
which has a speed ratio of approximately 3 to 1 between cruising and fishing
speeds. In such cases centrifugal pumps cannot be used unless provision is made
for maintaining nearly constant pump speeds. A solution to this is the use of a
rotary pump, the output of which varies directly with speed . Pumps should
also be selected for resistance to sea-water corrosion. Dissimilar metals should be
avoided in impeller and casing. All-bronze and all-iron pumps or those with
1 8
neoprene impellers are commonly used . Unless the pumps are located beneath
both the tanks and the waterline of the vessel, they must be self-priming to be
of use for filling and emptying as well as circulating.
PIPING
The main considerations here are ease of cleaning and resistance to corrosion .
Polyethylene pipe is an ideal material in that it has a very smooth bore and is
not attacked by sea water. However, i t is usually necessary to use brass pipe
fittings and valves. There are several aspects of the piping system which require
particular a tten tion . These are :
1 . The pressure drop should be kept at a minimum by the use of smooth
pipe such as polyethylene , by keeping pipe sizes as large as possible , and by
avoiding unnecessary restrictions such as elbows and valves. Gate valves are
preferable to other types in that they do not restrict flow excessively.
2 . The overall length of all piping should be kept to a minimum, particularly
in the engine room or at any other location where it is exposed to high temper
atures which can cause heating of the brine in the off-cycle with consequently
accelerated bacterial growth . Pipes which are so exposed should be properly
insulated .
3 . Piping should be designed to provide for flushing o f a l l lines with fresh
sea water with connections to the tanks closed. All piping subj ect to heating
should be flushed if the refrigeration has been stopped long enough for appreci
able heating to take place . This will depend on the ambient temperature and
whether the pipes are insulated.
4 . Normally provision should be made to circulate the brine from the top
of the tank through the chiller and return it to the bottom. Perforated poly
ethylene hose makes an excellent strainer for the inside tank connections. Cross
over valves should be provided so that the flow can be reversed and brine pumped
from the bottom of the tank when it is desired to drain the tank. Circulating the
sea water by drawing brine from the bottom of the tank and returning it to the
top is equally satisfactory, but it has the disadvantage of being vulnerable to
p lugging of the submerged strainer. Our experience has shown that if the pumping
rate is adequate , circulation within the tanks is no problem. Pipe stubs with the
aforementioned polyethylene strainers attached are satisfactory and there is
no need for grids beneath the fish or at the end of the tanks .
Schematic drawings of a suitable piping arrangement for three tanks are
shown in Figs. 8 and 9. The 4-way valve which simplifies operation of the system
by eliminating several other valves , and the piping loop which ensures constant
circulation in al l pipes while the circulating pump is running are worthy of note .
1 9
92162-7-5
FIG. 8. Piping arrangement for circulating refrigerated sea water from the top of the tank into the bottom.
20
'" "" ...... Ol "" I -l I Con "" �
N
W I N G TAN K
CIRCU LATING P U M P �
WING TANK
C E N T R E TANK
CHILLER
FIG. 9 . Piping arrangement for filling or emptying tanks, for flushing l ines, and for circulating refrigerated sea water off the bottom of the tank and i nto the top.
P RACTI CAL APPLICATIO N I N D I FFERENT FISHERIES
SALMON TROLLERS
Several reports have dealt with application of RSW to salmon trolling boats (Lantz, 1 953; Harrison and Roach , 1 954; Roach and Harrison , 1 95 8; Anon. , 1 9 5 7b , 1 959a , 1 960a). Results from observations and experiments with trollers operated by fishermen under close supervision by personnel from this Station have shown conclusively that RSW holding is practical and has many advantages over conventional methods. In fact , most of the advantages mentioned in the Introduction apply particularly to salmon trollers , which make extended trips to remote fishing areas. Many west coast trollers in British Columbia and in the United States have installed RSW systems during the past few years. This comparatively rapid development has meant that in many cases the fishermen and shipyards have unfortunately proceeded with an inadequate knowledge of the technology and engineering required to design a suitable RS\,y system. Among the mistakes which have been made are : ( 1 ) failure to provide for proper cleaning of the system ; (2 ) improper selection and design of refrigeration equipment, resulting in unsatisfactory cooling rates and holding temperatures ; (3) insufficient insulation ; (4) insufficient circulation ; (5) tanks which , when filled , have made the vessel unseaworthy. These mistakes have resulted in the delivery of a certain amount of spoiled fish , and unfortunately many people not in possession of the full facts have attributed these failures to th e RSW principle rather than the faulty design or maintenance of the particular installation. No one should attempt to install a RSW system without studying the available l iterature , consulting someone trained in marine engineering , and employing a refrigeration company with proven experience in the field . Above all , the fisherman should have a thorough understanding of the necessary procedures for cleaning the tanks and circulating lines.
The question of whether or not salmon tend to lose scales more readily during RSW storage on a troller , particularly in rough weather, is frequently raised . It appears that the maturity of the fish is the most important factor. Immature fish such as young coho salmon ( "bluebacks" ) and spring salmon (j ack springs) shed their scales very readily, whereas the scales of the large mature fish are relatively difficult to d islodge. I t has been noted that immature fish will lose scales i f rubbed against any rough obj ect including mature hard-scaled fish on decks and "checkers" , or during unloading. I f RSW tanks are filled up to the trunks or necks at all times , the water cannot surge and the fish are unable to move and chafe each other even in rough seas .
HALIBUT LONG-LINERS
In British Columbia three large new combination vessels primarily designed for halibut long-line fishing have been equipped during construction with RS\,y
23
installations , namely the Silver Viking (Harrison and Roach , 195 7 ) , the Pacific Ocean, and the Silver Viking II (Anon . , 1 958c , e) . Of these the best example is the steel -hulled Silver Viking II which completed by 1959 two highly successful seasons of hal ibut fishing , landing over 700 ,000 pounds of marketable fish during this period . Nearly all of these vessels' trips were to the more distant fishing grounds in halibut fishing areas 3A and 3B (the Bering Sea) where very large catches are available to vessels able to fish these remote waters. The RSW installation on the Silver Viking II is excellent and has performed in a very satisfactory manner. The success of this vessel and her predecessor Silver Viking has shown that RSW holding is practical for halibut fishing and has many desirable features . Observations on the Silver Viking II, where the latter part of the catch is stored in ice , clearly shows the RSW-stored fish to be of superior quality, although they are always a few days older than the iced fish . This means that an extra day or two of fishing is available before starting the long trip to port which may take 10 days, and one extra day may mean an increase of at least 1 0% in fishing time . Elimination of the laborious work of icing increases the effectiveness of the crew and makes possible larger catches in periods of good fishing.
SALMON PACKERS
In British Columbia and Alaska RSW-equipped salmon packers have been operated for several years with excellent results. The packer J.R.D. was equipped with three aluminum tanks having a combined capacity of 50 , 000 lb of salmon , and has been in regular service since that time (Harrison and Roach , 1 955 ) . American vessels equipped with this system include the M. V. Snow Mist (Anon. , 1 9 5 7a) , the Theo E (Anon . , 1 960b , c) , the self-propelled barges Dorothea (Anon . , 1 955a) and Jimbo (Anon . , 1 958b) and a scow operated b y Libby McNeill & Libby (Anon . , 1 955b) . The power scow Jimbo is perhaps the largest of these and is designed to hold 450 ,000 lb. It appears likely that the use of RSW for holding salmon destined for canning will become standard practice , at least while the present fishing regulations continue. The great advantages derived from the use of these large packers or salmon tenders is that they can pick up fish in areas far from the cannery, chill them rapidly and hold them at low temperatures for periods up to a week. This eliminates smaller fish packers , greatly reducing the demand for ice. Ice cannot be employed to the best advantage due to the large mass of fish handled , and use of RSW permits canneries to smooth out their working hours since the fish packers can be unloaded at any convenient time . Improved methods of unloading fish from the tanks have been developed which utilize unloading gates and high-speed bucket elevators . On the vessels J.R.D. (Harrison and Roach , 1955 ) and Silver Viking (Harrison and Roach , 1 957 ) salmon were removed conveniently and easily by brailing.
There is one aspect of the use of RSW for salmon packing which must be watched . This is the oft-occurring situation where a large load of slimy warm fish is rapidly filled into tanks. Since the ratio of fish to sea water is very high , the sea water becomes very heavily contaminated with protein and fish blood
24
and with spoilage bacteria from the slime and visceral cavities of the fish . This creates a heavy bacterial inoculum in a favourable growth environment . Under these conditions , even in a week at 30° F , unpleasant odours may develop in the sea water which indicate a serious bacteriological risk if the fish are stored further . If practicable , the contaminated sea water should be replenished with fresh clean sea water soon after the fish have been loaded into the tank .
SHORE TANKS
RSW storage has proven very useful in salmon canneries where tan ks are used to replace conventional fish bins (Anon . , 1 95 7a ,c; 1960d) . Salmon canneries are often faced with a severe problem of gluts caused by a short "fishing week" , which often extends for only 2 o r 3 days . Consequently large amounts o f fish must be processed quickly to prevent spoilage because ice supplies are seldom adequate to permit icing the fish . This of course means operating a cannery night and day for short periods during which employees must work long hours , including much overtime. Refrigeration of the surplus fish by RSW can be a solution to this problem in very large canneries . Tanks and equipment to refrigerate the fish which must be processed are necessarily very large and expensive and present certain design problems. One problem is to ensure adequate circulation in the deep tan ks which would be required to store large volumes of fish economically. For best results it would probably be advisable to provide auxiliar:y circulation through the mass of fish to prevent "hot spots " .
Shore tanks are also used for short-term holding of other species of fish . They have proven useful for holding and precooling halibut at freezing plants during periods when the freezers were overloaded . They are used in some Oregon filleting plants for short-term holding of round cod and sole before processing (Anon . , 1 959b) , and in some Newfoundland filleting plants where it has been found that the precooling of small codling gives improved firmness for machine filleting. The conversion in 1 958 of the 68-ft halibut schooner Western to use RSW was recently described by Autio ( 1 960) . In spite of problems created with trawled soles and other ground fish which were often covered with slime and fine sand or mud , the operation proved highly successful . Small shore tanks are also used by some mink ranchers for preserving fish and fish scrap which form a large proportion of the mink food ration. RSW equipment is much less expensive for this purpose than is freezing equipment (Anon . , 1 956b) . The use of RSW for preserving tropical species of fish was investigated in Ceylon by Lantz both on shore ( 1 955 ) and on a fishing vessel ( 1 956) with good resu lts .
Certain mechanical problems must be avoided in designing storage tanks for use with RS\iV. Frothing may occur due to proteinaceous material dissolved in the brine , but this can be avoided by submerging the brine return and ensuring that the suction lines are air tight . For precooling and operation with the tank partly fil led it would be necessary to return the chil led brine to the top of the tank. Tanks which have suction outlets at the bottom will require adequate strainers or grids to ensure against stoppages at the intakes. The use of ice without mechanical refrigeration requires special means for dissolving the ice
25
efficiently. This may be done by installing a separate small ice bunker or tank and recirculating the RSW through it (Huntsman , 1 93 1 ) . Another system which can be employed is the use of a floating perforated suction line made with a length of large-size polyethylene pipe. Care must be taken to provide sufficient perforations to ensure adequate flow to the pump suction and prevent frothing. With this system crushed ice may be added directly to the tank .
TRAWLERS
Small-scale experiments have been conducted using trawl-caught fish such as sole , l ingcod and gray cod with promising results . The chief problem with certain of these fish is weight gain during prolonged storage in RSW. This will be discussed later. For short periods weight gain is not serious with lingcod or gray cod but flounder species may present a difficult problem . Two Oregon trawlers and one Puget Sound vessel are successfully using RSW storage (Anon . , 1 956b; 1 959d) . I t seems probable that RSW may eventually be used rather extensively in the groundfish industry. There is no doubt that its advantages of rapid cooling, low temperature holding and prevention of crushing are very desirable and should lead to its wide-spread adoption for food fish , and even for scrap fish such as may be used for feeding fur-bearing animals , if sufficient care is taken in selecting fish species and l imiting storage periods.
Expriments carried out in Great Britain (Anon . , 1 959c) have shown that codling stowed in aerated sea water at 3 2 ° F (0° C) spoil somewhat less rapidly than do those held in ice at an ambient temperature of 36 . 5 ° F ( 2 . 5 ° C) . Practical trials in a trawler in which ice was used to cool the sea water and aeration was employed did not yield such encouraging results , and it was felt that the excellent icing methods commonly employed on British trawlers were as satisfactory as storage in RSW. However, the early development of off-odours in these trials is not consistent with data which have been reported in other fisheries , and it is possible that use of mechanical refrigeration could have yielded better results. I ndeed , the report mentions severe temperature stratification in some experiments causing exposure of fish to temperatures as high as 5° C (41 ° F) . A more careful investigation using a properly designed mechanical system might have yielded more favourable results. Experience at this Station has not indicated that aeration of the sea water , as carried out in the above trials , causes any quality improvement in fish held in RSW (Southcott et al . , 1 9 5 7 ) .
SALMON SEINING
The combination vessel Silver Viking during two seasons of salmon seining brought in all of her catch in RSW. This afforded an excellent opportunity to assess the potential of this equipment which , although installed primarily for halibut fishing , was available for use while the vessel engaged in other fisheries. Certain definite advantages were evident. All fish delivered to the cannery at the end of the fishing week were in exceptionally fine condition . In fact , the spring , coho and chum salmon normally were of as good quality as prime trollcaught fish . If these fish had been dressed on the vessel as is done on salmon
26
trolling boats they could undoubtedly have been marketed in competition with troll-caught fish . If the fish were not dressed the presence of large numbers of feeding spring or coho salmon in the catch had adverse effects on their externa l appearance i n that i t seemed to promote loss of the scales. This , however, was superficial and did not affect them as cannery fish .
SHRIMP
Higman and Idyll ( 1 952 ) carried out what appears to be the first thorough comparative study of shrimp held in RSW and in ice. In most of their experiments the temperature of the RSW was held at about 31 ° F. This is somewhat h igher than their recommended temperature range ( 28 . 5 to 30° F) . They conc luded that beheaded shrimp held in this medium were of acceptable quality approximately 2 1 days after the commencement of the experiment , while those held in ice were unacceptable after 15 days . Eventual ly, unpleasant odours developed in the RSW in which the shrimp were held , especially when rather e levated temperatures were used . The rate of development of such odours , or of deterioration generally, was not lessened when 1 5 % of the sea water was changed daily. When all the sea water was changed every third day there was no organoleptic improvement in quality, and the shrimp became noticeably tougher than
s hrimp held in unchanged sea water. The authors mention that the method was abused on two shrimp boats where the RSW temperatures ranged from 34 to
40° F and in one instance 25 -day old shrimp were landed . I t is difficult to deter
mine whether the method has ever been adopted to any extent commercially for holding Gulf of Mexico shrimp. In 1 954 Roach and Harrison published the results of a study in which British Colu mbia shrimp were held in RSW on a fishing vessel . I n preserving shrimp in this way it was found that the swelling of the flesh which occurred within the shell during its immersion in the RSW made conventional hand picking of the shrimp meat so difficult that i t was impractical . The shrimp remained in good condition for at least one week at 31 ° F. Recently the development of a fairly large shrimp-canning industry in Washington and Oregon has resulted in the introduction of shrimp-peeling machinery and i t has been found that shrimp held in RSW are easily handled by the machines. Since it is very difficult to ice shrimp adequately on the fishing vessels , RSW tanks are considered as a logical solution to the problem (Stern , 1 958) .
CRABS
The method of holding l ive crabs in RSW (Fig. 1 0) appears practical and has certain advantages (Roach , 1 956) . However, the problem of providing continuous circulation of the sea water is difficult to solve , particularly on small fishing vessels. The crabs wil l soon die if left in stagnant water, so the only alternative is to drain the tanks when circulation stops . One load of crabs brought in by a commercial vessel was held from the time of catching in circulating RSW at 30° F with no particular effort being made to keep the crabs alive . These crabs , a lthough many seemed lifeless , appeared in good condition when unloaded and were cooked and processed. Although dead crabs are normally discarded in
27
FIG. 1 0 . Live crabs being loaded into the hatchway of a tank of refrigerated sea water on board a carrier vessel .
processing plants because they spoil rapidly , those that had been held in RSW were stil l j udged acceptable by the grader who used his own organoleptic standards to grade them.
HERRING
This Station has carried out storage tests with herring held in RSW for d ifferent purposes . The preservation of fresh herring for bait has been studied most extensively. Tests showed that round herring remained almost unchanged in appearance and did not spoil when stored for periods of over 2 weeks in RSW. These results verify early experimental work (Sigurdsson , 1 945 ) . However, the first time fresh bait herring were stored on the Silver Viking during a halibut trip they spoiled rapidly although held at 30° F . These were summer-caught actively feeding herring in which the digestive tract autolysed rapidly. On later halibut trips when fresh , non-feeding herring were used , the bait remained in good condition for somewhat more than 2 weeks .
Other potential uses are storage for reduction purposes as has been begun on the Atlantic seaboard of the United States (Anon . , 1 958d) and as an adj unct to herring-canning operation s or to sardine-canning operations as mentioned 111 the Introduction.
28
PHYSI CAL AND CHEM I CAL CHANGES
\iVEIGHT CHANGES AND THEIR CONTROL
It is well known that fish flesh immersed for a short time in ice water (Tarr and Sunderland , 1 940) and whole eviscerated iced fish (Cutting , 1 95 1 ) gain weight which is lost slowly during storage. Similarly, fish stored in RSvV gain weight , only in this case the increase is slow and continues for 2 or 3 weeks at -1 to 0° C. During the past few years studies have been carried out with both eviscerated and non-eviscerated )J orth Pacific species of fish stored in RSW and the results are given in Table I I I . Eviscerated fish usually gain more weight than non-eviscerated fish . Most of the varieties studied did not gain weight excessively, and it appears that increases of from about 2 to 5% may be expected after 1 to 2 weeks storage . However , " flounders " , especially those which are " thin " , as after spawning, increase severely in weight , and it would be unwise to hold such fish very long in RS\V unless a practical and economical method of preventing this is discovered (see below) .
TABLE I I I . Weight increases in fish held in RSW (_1 0 to O°C) .
Days Weight gain Species stored C % ) Reference
Sockeye salmon ( R )* 3 1 . 4 Barker and Id ler ( 1 955 ) " ( R ) 6 2 . 7 " " ( E ) 3 0 . 8 "
Lingcod ( E ) 7 0 . 5 Baker et at. ( 1 95 8 ) " ( E ) 1 1 1 . 4 " ( E ) 1 4 3 . 8 ( E ) 1 8 4. 1 "
" ( E ) 20 4. 0 "
*R round ; E eviscerated.
29
An extensive study was made concerning the effect of dilution of sea water and of " artificial " sea waters made up of mixtures of inorganic salts on weight
increases in fish stored therein . A number of tests with sockeye salmon , halibut
and lemon sole showed that fish stored in half-strength sea water gained slightly
less weight than those stored in full-strength sea water. The differences were of the order of 10 to 1 5 %.
Rather extensive studies were made in efforts to control weight increases
which occur in RSW. After studying a number of substances it was found that one
of them (molecular weight about 1 00 , 000) which is harmless and is often inj ected
in cases of shock as a blood plasma extender (polyvinylpyrrolidone) possessed the required properties . This substance , in 2% concentration , virtually eliminated
weight increase in lemon sole stored either in full-strength or half-strength RSW, where in absence of the agent the weight increase in full-strength RS\V was about
11. 5% (MacLeod et al. , 1960) . Calculations indicate that, at present prices, use
of this substance in RS\V would cost about 0 . 7 cent per pound of fish so held.
However , it is quite possible that future research could result in less expensive
treatments.
CHANGES IN SALT COMPOSITION
Fish flesh contains much more potassium chloride than sodium chloride
and the sodium and potassium ion content of the flesh of average sea fish differs
l i ttle from that of warm-blooded mammals. Variations with species , season , and
sexual maturity are quite marked . In general , the potassium ion content varies
between about 0 . 33 and 0 . 8% and the sodium ion between about 0 . 03 and
0 . 09%. These figures correspond to between 0 . 63 and 0 . 92 % potassium chloride
and between 0 . 076 and 0 . 229% sodium chloride (McBride and MacLeod,
1956a, b ) .
\Vhen fish are stored in RSW there is an increase in their sodium salts
content and decrease in potassium salts content . The overall picture is, however ,
one of increasing concentration of total salts. Thus , experiments with eviscerated
coho salmon showed that the sodium ion content (expressed as percentage of
1.65 , and 4 weeks , 1 . 49 (McBride et al . , 1955 ) . Subsequent experiments with
round and eviscerated sockeye salmon showed that the sodium ion content in
creased more with eviscerated than non-eviscerated fish , and that the increase was
greater in full-strength than in half-strength sea water . Experiments with eviscerated halibut and round sockeye salmon showed that after 1 - and 2 -week storage periods the content of total salts was higher in the layer of flesh nearest the skin than in the interior layer (MacLeod et al. , 1 960) . Experience with halibut has indicated that , even with fishing trips of several weeks duration , the flesh does not become significantly "salty " . It is apparent that salt increase will vary with different fisheries and will be influenced by the species , holding time and whether the fish are or are not eviscerated . In conclusion , it is obvious that,
30
with a ful l tank of fish , where the ratio of fish to sea water will normally be about
3 : 1 or 4 : 1 , the average uptake of salts by the fish is unlikely to exceed one
quarter or one-fifth that of the sea water itself, namely about 0 . 7 to 0 . 9%.
Loss OF l'\ ITROGENOUS CONSTITUENTS
I t has been known for some time that fish stored in ice lose n itrogenous
constituents . These substances are probably made up of fish slime , and of proteins
and smaller residues such as amino acids which slowly leach from the muscle
tissue . In 1947 Dyer and Dyer reported that flesh of iced Atlantic cod lost from
1 · 8 to 3 · 8 % of the total protein and from 28 to 60% of the free amino acids .
Barker and Idler ( 1 955 ) found that non-eviscerated sockeye salmon stored in ice
l ost 2 · 5 % of their total protein in 7 days . In a study of salmon held in a com
paratively small volume of RSW for 6 days , these investigators found that the
following percentages of the total fish protein occurred in the sea water: noneviscerated coho salmon , 1 · 3; eviscerated coho salmon , 3 · 3; non-eviscerated
sockeye salmon , 1 · 2; eviscerated sockeye salmon , 3 · 2 . It also appeared that ,
where a few fish were stored in a comparatively large volume of sea water, greater protein losses occurred . As far as can be determined , l ittle further inform
ation concerning protein losses in fish stored in RSW has been published . In gen
eral , it appears that these losses are no greater than those usually found with iced fish. However, the experimental data are l imited and there is reason for further
in vestiga tion .
AUTOLYSIS
I t is wel l known that the flesh of non-eviscerated fish which l ies near the
visceral cavity may become soft or autolysed , especially if the fish have been feeding heavily prior to capture. This change is often very obvious with herring,
immature coho salmon (bluebacks) and tuna, and has sometimes been referred to as " belly burn" . Few data concerning the comparative severity of autolysis
of non-eviscerated fish held in RS\V and in ice appear to have been published .
Barker and Idler ( 1 955 ) found that autolysis , as j udged by increase in the free
amino acids in the belly-flap muscle of non-eviscerated immature coho salmon stored in ice, proceeded much more rapidly than in non-eviscerated sockeye
salmon held under similar conditions. They concluded that it would be unwise to
store uneviscerated feeding coho salmon for more than 3 days in RSW. In later
work Ronald et al. ( 1 95 7 ) made a study of sockeye salmon caught while actively
feeding and stored uneviscerated with and without slit belly cavities. These
fish were stored in RSW with and without 1 . 5 parts per mill ion (ppm)
of the antibiotic chlortetracycline (Aureomycin , CTC) . From determinations
of the increase in free amino acids in the belly flap muscle and from visual obser
vations , it was concluded that autolysis commences by the third day and is
marked after 7 days storage . In these experiments autolysis appeared to be
significantly delayed in the fish stored in the CTC-containing sea water , and it
3 1
was suggested that bacterial action may account for part of the so-called autolytic changes. However, further work is required to settle this point satisfactorily . I t is interesting to note that tests indicated that even after 14 days storage in RSW the salmon yielded an acceptable product on canning. However , curd formation was very marked with fish stored for this length of time (Schmidt and Idler , 1955 ) .
3 2
BACTERIOLOGICAL SPO ILAGE AND ITS CONTROL
S POILAGE RATES AS COMPARED WITH ICED FISH
I t has been tacitly assumed by some that storage of fish in RSW is an almost
infallible method of preserving them from spoilage for many weeks , and that it
will always retard bacterial spoilage much more than does storage in ordinary ice .
Such assumptions are dangerous and have undoubtedly led to a number of
practical fishermen either discontinuing use of RSW on their vessels or in
fluencing other vessel owners not to install such a system . As pointed out in the
Introduction , RSW has many distinct advantages over holding fish in ice , but
only if certain conditions are carefully observed . One of these is the control of factors which tend to accelerate bacterial spoilage .
In preliminary trials it was found that fish stored in RSW spoiled less
rapidly than fish stored in ice . The addition of either CTC (2 ppm) or sodium
nitrite (200 ppm) to RSW improved its effectiveness as a storage medium,
but the latter caused certain undesirable changes in the appearance of the fish
(Lantz , 1 953; Boyd et al . , 1 953 ) . In a later experiment (Gillespie et al . , 1 954)
i t was found that , as determined by bacterial counts , eviscerated coho salmon
stored on a fishing boat in RS\V spoiled slightly more rapidly than those stored
in crushed ice. In view of subsequent experience there is l ittle doubt that this
situation may easily arise where there has been inadequate cleaning and dis
infection of RSW tanks and associated equipment, where highly contaminated
very feedy fish are introduced , or when the temperature is not maintained
at about 30° F (- 1 . 1 ° C) . Subsequent research where favourable conditions for
comparative experiments prevailed has shown that, from the bacteriological
standpoint at least, RSW storage normally results in a product which is of better
quality than that which may normally be expected from average good icing on
fishing vessels (Tarr et al. , 1 954; Steiner and Tarr, 1 955 ) . Strictly comparative
data are d ifficult to obtain since with iced fish the conditions of icing and resulting
temperatures , and the washing effect of the water from the melting ice, are not
easily duplicated . Similarly , even if a temperature of 30° F is carefully main
tained , the initial bacterial contamination of the sea water by the fish is difficult
to keep constant, and this must influence the subsequent rate of spoilage . How
ever, if al l conditions are kept as ideal as possible , the other factors which were
previously enumerated as favouring the use of RSW must also be taken into
account in determining what method of storage is to be employed . I t is probable
that replacement of contaminated sea water with clean , chil led sea water soon
after fish have been loaded may exert a favourable effect on their subsequent
keeping quality.
33
ANTIBIOTICS
In the preceding section mention was made of the value of CTC in retarding bacterial spoilage of salmon held in RS\V. Further studies have confirmed and
extended these findings . However, the beneficial effect which results from addition of CTC to sea water is by no means as significant as that which is found when
ice containing the antibiotic is compared with ordinary ice . Experimental work
has demonstrated that 1 to 5 ppm of CTC added to sea water delayed spoilage of eviscerated rock cod . At this concentration there was no great difference in
the bacterial populations of the treated and untreated fish . However, when sensory j udgment was employed , fish from the CTC-containing sea water were
definitely of better quality than those from the ordinary sea water . In these tests CTC proved to be more effective than the other tetracycline antibiotics
(Southcott et al. , 1 9 5 7 ) . Later experiments with eviscerated l ingcod in which
10 ppm of CTC were added to one of two tanks of RSW showed that the treated
fish spoiled less rapidly than the untreated fish as j udged by sensory criteria , and
also in nearly all instances had lower bacterial counts . The value of the tetracycl ine antibiotics (CTC, oxytetracycline and tetracycl ine) in retarding spoilage
of salmon intended for canning, and for lemon sole (Parophrys vetulus) , was
amply demonstrated in experiments by Stern et al. ( 1 95 7a , b ; 1 958 ) , in which
these fish were held in 3% salt solutions with and without antibiotics. These
investigators used from 5 to 20 ppm of the antibiotics in their work and found no
significant difference between the tetracyclines. B ulletin I'\o. 1 24 of this Board
(Tarr, 1 960) discusses the use of antibiotics as preservatives for fresh fish .
A number of studies concerning the antibiotic residues which occur in
fish held in RSW containing CTC, and of their destruction during cooking, have
been made by Canadian , Japanese and United States investigators . These have
been thoroughly reviewed , as have also the presently permitted legal uses of antibiotics in fisheries (Tarr , 1 960) .
IM PORTANCE OF PROPER CLEANING AND SANITATION
Undoubtedly some of the failures which have occurred with RS\V installa
tions may be attributed directly to lack of proper sanitation . Fish properly packed
in ice are subj ected to a continual bathing in comparatively clean ice cold water,
while those held in tanks of RSW are normally exposed to a comparatively
small volume of water (e .g . only one-quarter to one-fifth of the weight of the
fish) which is initial ly contaminated with sl ime, blood and bacteria from the
fish. It is for this reason that it is absolutely essential that every precaution be taken to keep RSW installations thoroughly clean , and to observe procedures
designed to keep the initial bacterial contamination of the sea water to a mini
mum. As yet there is no proper scientific information available concerning the
effects of unsanitary conditions on the rate of bacterial spoilage of fish in RSW.
However, there have been many observed verbally reported instances where the
fish del ivered have been of very poor qual ity and have either been rej ected or
34
barely passed inspection . With vessels which have adopted good cleaning and pro
per sanitary measures , and whose refrigeration equipment has functioned pro
perly , there is little or no danger of serious spoilage of fish for at least 2 and even 3 weeks, though it is felt that it is undesirable to extend the holding period for over
2 weeks . A very important point which cannot be overemphasized is that ,
while with iced fish only part of a load may spoil , with fish held in tanks of RSW
even under proper conditions there is a danger that all or nearly all the fish wil l
be rejected i f spoilage occurs . I t i s suggested that the following conditions be
observed for vessels using RSW tanks.
After fish are landed and before the tank surfaces dry, the tanks , heat
exchanger (s) and pipes must be flushed with clean , cold , fresh or sea water
in order to remove fish scales, slime , etc . Water near fish docks is usually quite
unsuitable for this purpose . Following this , all adhering particles of fish or slime
should be scrubbed from tank surfaces, using an alkaline washing solution.
A number of suitable commercial cleaners which usually contain alkaline salts
such as sodium metasil icate , or trisodium phosphate (TSP) , plus a surface
active agent are available from reputable dealers . This cleaning may be carried
out with a steam gun if available . The condensers and pipes must also be flushed
well since these are potential sources of bacterial contamination. After flushing
with clean water a spray of some good germicidal solution should be applied to
the tank surfaces and circulated through the pipes and condensers . Suitable
germicides such as an alkaline hypochlorite , a quaternary ammonium compound
or a germicide containing available iodine are usually quite satisfactory. However
hypochlorite cannot be left in contact with metals , and for this reason it is usually
wise to employ one of the other types of germicide . It is good practice to leave
weak solutions of the non-corrosive disinfectants in the pipes and condensers
which must be flushed with clean sea water prior to filling tanks before fishing .
This procedure avoids danger of a focus of infection developing. I f antibiotics
are employed , proper cleaning and disinfection are absolutely essential to avoid development of resistant bacteria.
The following list of instructions , which were prepared in order to stand
ardize the cleaning procedure for the Silver Viking II between halibut trips , may be applied to any RSW system which employs multiple tanks , external chillers
and circulation pipes :
A . Preliminary Cleaning:
(By crew) during unloading-
1 . Hose down all surfaces with fresh clean water.
2 . Crew members scrub tanks with TSP or l iquid soap 111 hot water,
using scrub brushes.
3 . Fill two aft tanks with clean , fresh (not harbour) water.
4 . Flush out pumps and l ines , using this clean water.
3 S
B . Flushing:
(By cleaning crew) after unloading-
1. Pump from top of filled tanks overboard for a minute or two , then circulate top to bottom for a few minutes .
2 . Pump from top of one filled tank into bottom of an empty one on the other side through the cross-connecting l ine. Let water run into bilge .
3 . Pump from bottom of filled tanks overboard for a minute or two .
4. Pump from bottom of filled aft tanks into top of the middle tanks , then into top of forward tanks . Let this water run into the bilges .
5 . Pump from bottom of filled tank into top of an empty one on the other side through the cross-connecting l ine. Let run into bilge.
6 . Stop pumps. Open all valves to bottom of tanks; let run for a minute or two to flush . Let go to bilges . The above procedures will flush all l ines.
C. Sanitizing:
(By cleaning crew)-
1. Let water run into the two forward or mid tanks from the aft tanks until pumps are primed . Add TSP (5 lb) and bleach (t gal lon of 1 0 % sodium hypochlorite) to each and circulate 1 5 minutes bottom to top to clean chil lers . Let go into bilge.
2. Let water run into the same two tanks till pumps are again primed. Add 1 gallon of a suitable sanitizing agent to each of these tanks and circulate for 15 minutes . Pump through top connection and then the bottom connection into the other four tanks . Drain remaining water into bilge .
3 . Spray all tank surfaces with a strong sanitizing solution .
3 6
REFERENCES
ANON. 1 9 5 5a. Seldovia Bay tender to carry salmon in chilled water. Pacific Fisherman, 53 (6 ) : 5 9 .
1 955b. Sea-water chilling outfit installed on Libby scow. Pacific Fisherman, 53( 1 1 ) : 1 8 . 1956a. Regulations respecting t h e construction a n d inspection o f fishing vessels not
exceeding eighty feet registered length. Dept. of Transport. Queen's Printer, Ottawa, 38 pp.
1 956b. Chilled sea-water well saves time, fish , money. Pacific Fisherman, 54( 1 1 ) : 26 . 1 95 7a. Sea-water chill ing-Saves fish , saves money, saves work, time, quality. Pacific
Fisherman, 55( 9 ) : 29. 1 95 7b. )Jo more ice for Sally. Pacific Fisherman, 55( 5 ) : 42 . 1 95 7c . Nelson's new Paramount plant . Western Fisheries, 54( 5 ) : 1 2 . 1 95 8a. 75-foot seiner designed from research model. The Fishboat, 3 ( 7 ) : 43 . 1 95 8b. How can you make it , fishing 8 days a year? Pacific Fisherman, 56( 1 1 ) : 1 8 . 1958c. B i g Canadian catches shatter halibut records. Pacific Fisherman, 56( 9 ) : 2 1 .
1 95 8d. Pogie boat pioneer in design, construction. The Fishboat, 3( 7 ) : 44. 1 958e. Silver Viking II is a world beater. Western Fisheries, 55( 6 ) : 1 2 . 1 959a. 38-foot troller Justine bristles with equipment. Western Fisheries, 58(4 ) : 1 9 . 1 959b, Area Report, Coos Bay. Pacific Fisherman, 57( 5 ) : 2 7 . 1 959c. Handling a n d preservation o f fish. Torry Research Station. A nn. Rep, for
1 958, pp . 5-6.
1 959d. Sea water chilling listed by North Pacific trawlers . Pacific Fisherman, 57( 1 3 ) : 26 ,
1960a. Nev,- troller has hydraulically driven chiller. Western Fisheries, 60(4) : 2 2 . 1 960b. Newly refrigerated "Theo E n hauls fresh Alaska salmon to Seattle. Pacific
Fisherman, 58( 7 ) : 20 . 1 960c. The great Bristol Bay red salmon run of 1 960. Pacific Fisherman, 58( 9 ) : 7 .
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ACTIO, PAUL. 1 960. Commercial brine chilling operation for bottom fish. A bstracts of papers presented at the 1 1th A nnual Conference, Pacific Fisheries Technologists, March 28-30 (mimeographed by Bureau of Commercial Fisheries , Technological Laboratory, Seattle , Washington) , p. 3 .
BAKER, E . G. , B . A. SOUTHCOTT A�D H . L. A. TARR. 1958 . Effect of chlortetracycline ( CTC ) antibiotic on the keeping quality of lingcod stored in refrigerated sea water. Fisheries Research Board of Canada, Prog. Rep. Pacific Coast Sta. , :\To. 1 1 2 , 1 5-1 7 .
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3 7
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-
3 8
ROACH, S. W. o AND HARRISON, J . S. M . 1 954. Use of chilled sea water and dilute brines in place of ice for holding shrimp aboard a fishing vessel . Fisheries Research Board oj Canada, Prog. Rep. Pacific Coast Sta . , No. 98, 23-24.
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RONALD , A. P. , D . R. IDLER AND E. HRUSHOWY. 1957 . Storage of round and slit sock-eye salmon in refrigerated sea water with and without Aureomycin Fisheries Research Board oj Canada, Technological Station, Vancouver. Mimeo. A nn. Rep. Jor 1956-57, pp. 8 1-84.
SCHMIDT, P . ] . , AND D. R. IDLER. 1955 . Transport and storage of fish in refrigerated sea water. I I I . Curd in canned salmon as related to post-mortem age of fish. Fisheries Research Board oj Canada, Prog. Rep. Pacific Coast Sta. , No. 1 04, 9-10 .
SIGURDSSON , G. J . 1 945. Studies on the storage of herring in refrigerated brine. Proc. Inst. Food Technologists, pp. 9 1-1 14 .
SOUTHCOTT, B . A . , E. G. BAKER , J . W. BOYD AND H. L . A. TARR. 1957 . Comparative effectiveness of tetracycline antibiotics for fish preservation. Food Technol . , 1 2 : 1 08- 1 1 0 .
STEINER, G. , AND H. L . A. TARR. 1 955 . Transport a n d storage of fish in refrigerated sea water. I I . Bacterial spoilage of blue-back salmon in refrigerated sea water and in ice, with and without added chlortetracycline. Fisheries Research B oard oj Canada, Prog. Rep. Pacific Coast Sta . , No. 1 04 , 7-8.
STERN, J . A. 1 958. The new shrimp industry of Washington. Proc. GulJ and Caribbean Fish Inst. , 10th A nnual Session, pp. 3 7-4 1 .
STERN, J . A . , H. L . LEIBMAN, A . D . GRAUER, G . KUDO AND A . A . DACOSTA. 1957a. Com-parative studies of the effects of the tetracycline group of antibiotics in the preservation of fish. A ntibiotics A nn . , 1956-1 957, pp. 984-996.
STERN , T . A., H . L. LIEBMAN, G. KUDO, J . CHAPEL, R. A. OLSEN, L . L. FARBER AND M . GREN NAN. 1958. The potential application of antibiotics in the salmon canning industry. I I . Chemical and bacteriological evaluation. Food Technol. , 12(3 ) : 1 32-13 7 .
STERN, J . A . , H . L. LIEBMAN, R. E. M ULKELT AND B . HEATHERELL. 1 95 7b. The p o -tential application of antibiotics in the salmon canning industry. A ntibiotics A nn . , 1956-1957, pp. 975-983.
TARR, H . L. A. 1 947 . Preservation of quality of edible fish products. Fisheries Research Board oj Canada, Prog. Rep. Pacific Coast Sta. , No. 7 1 , 1 5-20.
1957 . Preservation of fresh fish. A rchiv. Jur FischereiwissenschaJt, 8 : 9- 1 2 .
1 960. Antibiotics in fish preservation. Fisheries Research Board oj Canada Bull. , No. 1 24 , 24 pp.
1961 . Chemical control of microbiological deterioration. Chapter in book on "Fish as Food", compiled u nder the editorship of G. B orgstrom . ( I n press. )
TARR, H . L . A . , J . W . BOYD AND H . M . BISSETT. 1 954. Antibiotics i n food processing. Experimental preservatives of fish and beef with antibiotics. J. A gric. Food Chem. , 2 : 3 72-3 75 .
TARR, H . L. A . , AND .T . S. M . HARRISON. 1957 . Transport and storage of fish in refrigerated sea water. A nnual Review and Program, Fisheries Council oj Canada, pp. 35 , 37 , 39 , 4 1 (April ) .
TARR, H . L . A. , AND P. A. SUNDERLAND. keeping quality and to prevent drip. Pacific Coast Sta . , No. 44 ; 12-14.
1 940. Brining fillets in order to enhance Fisheries Research Board oj Canada, Prog. Rep.
39
APPEN DIX I
EXPERIM ENTS O N THE STORAGE OF CANAD IAN ATLANTI C COAST COD I N REFRIGERATED SEA WATER
By W. A. M ACCALLUM AND M. S. CHAN
Fisheries Research Board of Canada
Technological Station, Halifax , N.S.
The work reported in this Appendix is confined to studies on the preservation of cod in a refrigerated sea water medium and to important physical and chemical changes occurring in the fish flesh and carcass during storage . Results of storing Atlantic cod in ice and in refrigerated sea water (RSW) at 32°F both with and without the incorporation of an antibiotic are compared . Storage at 30°F in a salt-fortified RSW medium was also attempted with interesting results.
Particular reference is made to probable acceptance and sales of the stored fish , bearing in mind Government of Canada Standards for quality. Flavour, odour and other organoleptic changes are noted together with salt penetration and the influence of the latter in regard to fillet taste and the by-products (fish meal) industry. Some of the results are similar to those reported by British ( Reay, 1 95 7 , 1 9 58) and Swedish (Lilj emark , 1 959) investigators . Results of U .S . Fish and \iVildlife Service investigations on the effects of holding ocean perch and whiting at 30°F in RS\;V and in ice have been reported as well (Cohen and Peters , 1 9 6 1 ) . \iVhile taste panel tests indica ted in the main that RSW -stored samples of these fishes rated higher at any one given time than samples stored in ice , and chemical tests in general showed correlation , the latter did not necessarily differentiate between RSW and iced samples at any one given point in storage.
In al l cases the cod used in our experiments were inshore caught , boated by hook, and refrigerated within a few hours after capture . Seventeen storage tests were conducted in which the fish were held either gutted or ungutted . Between 400- and 600-lb lots were used in each test .
The apparatus used for holding the fish in mechanically refrigerated sea water (Fig. 1) consisted of two tanks , the larger for the fish and the smaller for the Freon- 1 2 refrigeration coil . Fortified , natural oceanic , or diluted sea water was pumped from the smaller refrigerated tank into and uniformly over the bottom of the fish chilling tank where it could rise through the fish to be drawn off j ust below the top surface of the sea water by means of a flexible header system connected to a second pump. The capacity of each of the two pumps was capable of adj ustment , that of the pump discharging into the fish tank being maintained at a higher rate than that discharging into the tank containing the refrigeration coil . This was made possible by providing gravity flow from the larger to the smaller tank. The amount of sea water circulated by means of gravity represented
41
FIG. 1 . The top photograph is a top view of the insulated RSW and fish storage tank ( left ) and of the insulated smaller chilling tank (right ) , the two tanks having a common insulated cover.
The bottom photograph shows the relative sizes of the two tanks.
42
the difference in the set capacity of the two pumps. With this arrangement , a constant level of sea water in each tank was maintained . The suction header was held j ust below the surface of the water , thereby eliminating the danger of frothing . The rate of circulation of water through the fish was about t gal/min per 100 lb fish being stored .
The interior surfaces of the iced-fish storage box and the RSW box were made of aluminum alloy and epoxy resin coated wood and thus were ideal for effective cleaning practices . All surfaces including the interior of piping and pumps in contact with RSW were scrupulously washed and disinfected with chlorine solution , then rinsed with chlorinated tap water before and after each run .
Natural sea water containing close to 3 % total salts was collected at some distance from shore and was used in all experiments with RSW media. To ensure sanitary quality of the water , bacterial counts were performed on all water used . Bakers ' grade , fine evaporated salt1 was added to the sea water when a fortified medium was needed . Tap water was added to the sea water when a diluted medium was required .
The iced fish were placed in a box which in turn was located within an insulated container. The ambient temperature inside the latter was about 3 7°F. D rainage water from the melting ice in intimate contact with the fish was al lowed to collect below and out of contact with the fish but within the insulated outer box. The water was drained off periodically and rates of melting were established . Cooling rates and holding temperatures of the iced and RSW fish were recorded .
The antibiotic chlortetracycline (CTC) in the amount of 1 0 parts per mil l ion (ppm) was used in the treated seawater . Acronize FD (commercial grade, 1 0% active CTC , product of American Cyanamid Co.) was used in al l experiments employing CTC. For fish treated with antibiotic before icing, a 2-minute d ip in a solution containing 7 5 ppm was used .
GUTTED COD
PROTEIN LOSSES
RESULTS
According to Fraser , Mannan and Dyer ( 1 9 6 1 ) newly caught cod contains about 81 % water , 1 5 % protein , 2 . 5 % extractives , 1 . 3 % ash and 0 . 7 % fat . Since protein is the main nitrogenous constituent having food and nutritional value , the extent to which it is leached during handling and storage should be known . Our results are summarized in Table I . I t wil l be noted that the amounts of protein leached at 6 days from iced cod and from cod stored in 3% and 5% salt RSW were 1 . 1 , 2 . 1 and 1 . 8% respectively. These values might well be applicable commercially in cases where fish are iced in shallow layers , for example in shore storage . Under conditions of storage as encountered on the trawler, Dyer and Dyer ( 1 947) point out that bottom-stowed fish will be washed by relatively large
IMined at Nappan (near Amherst) , N .S . , Canada.
43
amounts of melting ice water and that one might expect fish from this location to be leached to a far greater extent than are top-stowed fish . It would be expected therefore that leaching losses as between RSW and iced fish aboard the vessel might be much closer than our results would suggest . Losses encountered during storage in both strengths of salt RSW mediums are quite comparable. The seemingly low amount of leaching in the 5% salt RSW might be attributed to the partially frozen condition of the fish muscle at about 30°F.
TABLE L Protein losses in gutted cod stored in crushed ice and in refrigerated sea water.
Percentage protein leached from fresh gutted cod after storage time i n :
Experiment Fish
storage temperature Crushed ice
Refrigerated sea water (3 % salt)
Refrigerated sea water (5 % salt)
6 days 12 days 6 days 12 days 6 days 12 days
1
2
3
1 . 2
0 . 9
1 . 1
3 . 1
2 . 5
2 . 3
1 . 9
2 . 0
4 . 6
4 . 3 Av. -�I-A--V-. --2-. -S- I -A-v-. -2-. -1 -::;v.-4-. 5-
Dyer and Dyer I ced a t r o o m ( 1 947) temperature
of 65°F
4 30°F
SPOILAGE
1 . S 3 . 3
1 . S 3 . 7
Trimethylamine (TMA) is one of the obj ectionable volatile nitrogenous compounds formed when fish decompose . The amount of TMA serves as a usefu l , but not infallible , index for the freshness of fish . The initial TMA in the samples of fish used was about 0 . 1 mg TMA-nitrogen per 1 00 g of fish muscle. This represents very fresh fish . With gutted , iced , trawler-caught cod , Castell et al. ( 1 959) have shown the following approximate relation between TMA values and organoleptic grading of cod landed from trawlers throughout the whole year.
TMA value (mg TMA -N/100 g
of muscle)
1 . 0 1 . 5 2 . 0 3 . 0 4 . 0
Percentage of
samples judged to be grade 1*
65 35 33 1 2
7
*For organoleptic grading (grades I , I I and I I I ) see Castell et al. ( 195S) .
44
I f one uses results obtained from landings made over a year, i t would appear that
there is better than an even chance of fish with a TMA value of 1. 5 being second
grade. We shall first assess the results of our holding experiments in ice and in
refrigerated sea water in terms of TMA development.
When no CTC was used iced fish showed slower TMA development than
fish stored in RSW, this difference appearing as early as 5 days in storage (Fig. 2 ) . I t was not until 9 days in storage (Fig. 3 ) that one could differentiate between
T MA development in the iced (no CTC added) and RSW (CTC added) stored
fish. By that time both groups had long since been passed to Grade I I by our
graders (see Organoleptic Evaluation below) . Thus it may be difficult if not
SEA WATER, : I'" I S IoI RI>.TIQ 0.5 : I HOLOI Nt;; TEMP 31° r
o 2. 3 4 5 6 7 6 9 10 II \1 I! 14 1 5 16 17 16 5TORAGE T\ME IN OA'<S
FIG. 2 . Trimethylamine development in eviscerated cod stored in crushed ice and in refrigerated sea water at 32 °F.
45
impossible to find significant differences in the TMA values of fish so treated within a period during which the fish are acceptable for the production of grade I fillets . The iced fish (previously dipped in CTC) showed a distinctive difference from RSW (CTC added) fish in regard to TMA content at 9 days , this tendency starting at about 5 days storage. There was a parallel relationship between organoleptic grading of samples of the two lots at 9 days also (see below) , the iced fish being quite superior in quality. The rate of TMA development was the same for cod stored up to 9 days at 30°F in fortified (5% salt) RSW and i l l ice at 32°F.
x---x - I CE D C O D D I P P ED PREVI OU SLY I N 75 P P M C T C F O R 2 M I N
0-0 - ST ORAG E I N R E FR I G ER ATED S E A WATE R CONTAIN I N G 10 P P M C T C
AVER A G E W EI G HT E V I S CER A TED C O D - 3 � LB
S E A WATER : F I SH R A T I O - 1 . 2 9 : 1
H O L D I N G TE M P - 3 2 O F
2 3 4 8 9 1 0 I I 1 2 1 3 14 15 1 6 17 1 8 S T O R AGE TIME IN DAY S
FIG. 3 . Trimethylamine in eviscerated cod stored in crushed ice , 75 ppm CTC dipped and iced, and in refrigerated sea water ( 1 0 ppm CTC ) at 32 °F.
46
ORGANOLEPTIC EVALUATION
The ultimate criterion in the evaluation of a fish food product apart from all chemical and physical tests is the organoleptic quality. This includes sensory factors of taste , odour , colour and texture , their sum total determining its final acceptabil ity.
Table II summarizes the organoleptic grades of gutted cod stored in ice at 3 2 °F , in 3% salt RSW at 32°F , and in 5 % salt RSW at 3 0°F. Partial freezing of the fish occurred at 30°F and the quality of the fillet was maintained somewhat longer under this condition. For equal storage temperatures , one would have expected that salt absorption by cod stored in 5% salt RSW would be greater than that found in fish stored in 3% salt RSW. By lowering the temperature of the former to 30° F at an RS\¥ : fish ratio of 1 . 3 : 1 , the rate of salt absorption was reduced so that actual increase in salt in the two instances was about the same (Tables I I and I I I ) .
Table I I I shows comparative grades o f iced , CTC-dipped , and RSW-stored cod and their relation to TMA and salt content . The " CTC-dipped and iced " treatment was the most effective method of storage , the fillets being still grade I at 9 days caught-age . H owever, taste panel assessment at this Board 's Halifax Technological Station (Table I I I and Fig. 4) indicated no statistical significance between the three treatments (Fig. 4) . The taste panel procedure followed in establ ishing percen tages of grade j udgmen ts was tha t described by Dyer and Dyer ( 1 949) .
1 00
8 0
60
� 4 0
20
- L E G E ND -
" 75 P P M CTC D I P A N D I C E D
STOR A G E
& I C E D S T OR A G E
• 3 '4 SALT RSW W I TH 1 0 P P M
C TC STO R A GE
I I I '4 GRADE ± STAN DA R D E R R O R 1 I I O F M E AN
TASTE PA N E L P R O C E DUR E
DYER A N D D Y E R ( 1 9 4 9 )
---
--- -- -i
o 2 3 4 5 6 7 8 9 10 I I 1 2 13 14 15 1 6 S T O R A G E I N D A Y S
FIG. 4 . Taste panel curves showing percentage grade of RSW-stored, "CTC-dipped and iced" and iced cod with storage at 32° F.
47
Treatment of cod
-,--
TABLE I I . Organoleptic evaluation o f gutted cod and cod fillets . . -Organoleptic grades .�----- Taste preference steamed fillets
Gutted cod Raw fillets (TMA values in brackets) ._------Cau ght-age of cod Cau ght-age of cod Cau ght-age of cod
(days) (days) (days) -----5 9 1 5 5 9 1 5 5 9 1 5
Percentage salt in fillet
Caught-age of cod (days)
5 9 1 5 -- -- ---- �-�-,,--- ---- ---- -------- ----Iced at 3 2 ° F . I I I ' I I I I (0.4) II ( 1 . 5 ) I I I + (4. 8 ) N o See 0 . 1 0 . 1 0 . 1
preference Note 2 Unacceptable RSW (3 % salt) at 3 2 OF
R l � 0 . 5 : 1 . I I I ' I I I I (0.3 ) I I (2 . 1 ) I I I ( 1 3 . 1 ) 0 . 3 0 . 5 1 . 0 --- --- ------ . -----"" ---- ----RSW
Iced at 3 2 of . . . I I I J.1 I I I I (0. 1 ) I I ( 2 . 0 ) I I I (8 .3) No (5 % salt) cod 0 _ 1 0 . 1 0 _ 1 preference preferred Unacceptable
RSW (5 % salt) at 3 0 °F over iced Rl � 1 . 3 : 1 _ . I I I I' I I I I I (0. 1 ) I I + ( 1 . 5 ) I I I ( 1 0 . 5 ) cod 0 . 3 0 . 9 1 . 9
I 1 R � Ratio of RSW to fish (by weight) .
2 Bad flavours i n iced and RSW sample s ; more s o i n the latter, these being easily distinguishable from iced samples. Salty taste i n RSW samples. A second taste panel was
� requested to remark on salt in similar samples from a subsequ ent experiment. Two of five panelists could distinguish RSW samples by the salty taste at 5 days (no downgrading) , 00 At 8 days. two panelists found RSW fillets to be objectionably salty and three very salty (the fillets actually contained 0 . 6 % salt ) .
� Slight (normal) sour odour o n round fi s h a t 9 days, first detected a t about 7 days caught-age. C haracteristic odo!lrs tended to b e present in fillets also.
4 Strong, sharp, seaweedy (rancid) odours on skin, gills, etc. at 9 days. This odour, \vhich appeared as early as 7 days caught-age, was found to be typical of RSW-stored cod. C haracteristic odours tended to be present in fillets also.
Treatment of cod held at 3 2 'F
---,-"----- ----Iced . .
RSW (3 % salt) + C T C (Rl � 1 . 3 : 1 ) . .
C T C dip + ice .
TABLE I I I . Organoleptic evaluation o f gutted cod and cod fillets.
Percentage of opinions from 1 4 to 21 j udgments
Grades of raw fillets of degree of saltiness of steamed fillets from
Grades of gu tted cod from cod of caught-age (days) cod of indicated cau ght-age (days)
at caught-age (days) (TMA val ues in parentheses) Salty .,- -------""-,-,-------- ,,----- -�-------.
6 9 ---- ---I I --- ---
1 6 ----I I I .-_ .. -----
6 9 ---_._------ ,----""'--"._-
] (0 .3) II ( 2 . 2 ) ----- ------II + I I I J ( 0 . 5 )
---t- ----
_ II +
(::.s2...1
I I - I I- I (0. 4) ]- ( 1 .0)
1 6 6 I 9 1 6
I I I ( 7 . 5 ) --- --
--- ------------
I I I ( 1 5 . 4) _ __ 5_ 1 __ 5 2
_
I I- (6.9) - -64
Objectionably salty
6 9
- 29
1 6
2 9
Percentage salt in fillets from
cod of caught-age (days)
6 9 --- ---0 . 1 0 . 1 --- ---0 . 4 0 . 9
0 . 1 0 . 1
1 6
0 . 1
I . S 0 . 1
The most significant results of the study of comparative treatments of cod were that the use of RSW did not appear to contribute to quality and the presence of "salt fish" tastes in the fish flesh could be detected at a caught-age of 5 days . Off-flavours were found to be obj ectionable in fish held for an additional 3 or 4 days (Tables I I and I I I ) .
Diluted RSW ( 1 . 5 % salt) was also tested a s a n alternative storage medium. After 4 days , the original sea water was replaced with a fresh diluted quantity. This did not improve the quality of the stored cod compared to fish stored in normal (3% salt) RSW. The cod stored in 1 . 5 % salt RSW were grade I I at 8 days caught-age.
UNGUTTED COD
Ungutted cod were held in 3% salt RSW containing CTC and compared with ungutted iced cod at intervals throughout their storage life. Table IV gives the organoleptic grades of the fish and of the raw and steamed fillets. The salt absorbed by the fish flesh (Fig. 9) was not a significant factor in taste assessment since proteolysis in the gut cavity resulted in down grading the fillets long before the panelists were able to taste salt . Similar proteolysis also occurred in the gut cavity of the iced fish .
TABLE IV. Organoleptic evaluation of ungutted cod and cod fillets. ( Ratio of fish to RSW = O.4 : 1 . )
Grades a t caught-age ( days ) Remarks concerning steamed fillets Treatment of cod held at Ungutted cod Raw fillets from cod of caught-age ( days )
32°F 4 6 8 4 6 8 4 & 5 6 8
------- -- -- -- -- --
Iced . . . . . . . . . . . I I - m I I - I I I Slight pref- - Significantly erence for spoiled
RSW ( 3 % salt ) i ced s a m - Quality bor-+ CTC . . . . . . I I-" I I I " I I I I I l I- m pIes. Qual- derline to
ity fair. acceptable
" When removed from the seawater the cod had the appearance of grade 1. As soon as the fish were cut, autolysis was obvious (at 4- and 6-day caught-ages) . Liver and gall bladder breakdown was noted, coupled with sloughing of belly wall , discoloration of fillet and off-odours in poke.
SALT ABSORPTION
Figure 5 shows the effect of size of gutted cod on salt absorption during storage in 3% salt RSW at 3 2 ° F . The salt in the fillets of small fish reached 0 . 5 % in 4 days while the flesh of large fish held in the same medium took 6 days to reach this level of salt . Figure 6 shows the effect of using three d ifferent weight ratios of RSW to fish , when the samples were stored under similar conditions in all other respects . I f a salt content of 0 . 5 % in the fillet was not obj ectionable , and this wi l l not be an established fact unless frozen storage or other experiments are done to measure the effects of sal t , cod may be stored for up to 8 days in 3 % salt RSW. O n this basis , the upper l imit t o storage ( 8 days) was achieved by e mploying a very low ratio of RSW to fish (Fig. 6) . After 7 days storage the same
49
\ . :; I . 2 -\ . 1 - o
2 . 9 - 2 · S
2 . 7 2 . 6 2 . 5
- 2 . 4 2 . 3 2 . 2 2 . 1 �
<{ 2 . 0 <II 1 . 9 �
� 1 . 8 z w
1 . 7 ?i! w 1 . 6 tl.
1 . 5 1 . 4
�
I
:�= /��� _ _ � ..J .8 - �//'" "_ -� ¥ /' . .- -1 CD R E FR I G E RAT E D
� ::= o�.�/./ ! �I�L�L
C
E���E R
w .5 - - o:-� "� i THRESH O L D F O R F I S H � 4 � tg! � M E A L P R OD U C T I ON W • -t: /" AVG. W T. E.V I SCERATE.D C O D
p. . 3 - • /" • S M ALL - 3 Y. LB � 0 M E D I U M __ 2 4 Y4 lB .2 - /' '" lARGE 5 LB
x VERY LARGE --- 6 % lB . 1 -
-- S MALL C O D !-I -I -I-I---
I---
I--� - - C O M M ON TO A L L L A R G E R C OD
I I I I I I I o I 2 3 4 5 6 7 8 9 10 I I 1 2 13 14 15
S T O R A G E T I M E I N D A Y S
FIG. S . Effect of s ize of fish on the salt content of fil let and carcass of eviscerated cod stored in refrigerated sea water at 32°F.
CD R E F R I G E R A T E D S E A WATE R C O D 2 � L B
® C A RC A S S @ F I L L E .T
- - - - - - EXTRAPOLAT E D USING LAR G E R
2 3 4 5 6 7 9 S T O RA G E T I M E I N DAY S
FROM DATA OBTA I N E D F I S H .
Effect of three weight ratios ( R) of sea water : fish on the salt content of eviscerated cod and of the refrigerated sea water medium.
5 1
� 1 . 8 ...J ...J La.. z 1 . 6
0 z c:t I. 4 (/J (/J c:t (.) a: 1. 2 c:t (.) Z
!:j 1 . 0 c:t (/J I-Z l&.I (.) a: l&.I 0..
0.4
0.2
I R - 1 . 28 �l� R - 1 .55 � R - 1 . 9 1 �
c:t l&.I (/J z I-..J c:t (/J
5
4.4
AVG. WT. EVISCERATED COD 5 . 5 LB.
( 1) REFR I G E R ATED SEA WATER ( 5 "X. N
(U) CARCASS
(lID FILLET
(rl) THRESH OLD FOR F I S
R - BRINE I F I SH R AT I
SEA WATER -J :I' T E M P 30.5 ° F - I 2 4 5 6 7 8 9 1 0 I I 1 2 1 3 14 15
STOR AGE TIME I N DAYS
FIG. 7. Salt absorption in eviscerated cod stored in refrigerated sea water ( 5 % salt ) a t 3 0 and 30 . 5 ° F.
52
1 .5
1 . 4
1 . 2 N E W � STR E N GT H SEA WAT ER
1 .0
!:J « (/) I-Z W (.) 0:: W 0..
0.4
0. 2
LEG E N D
2 3 4 5 6 7 8 9 10 I I 1 2 STORAGE T I M E I N DAYS
AVG. WT. EV ISCE R AT E D C O D ....... SMALL - 3 LB 0-0 M E D I U M - 4.5 L B c:>--<:> LAR G E - 7. 3 LB
(!) HALF- STR E N GTH R E F RI GERATED SEA WAT ER
(m CARCASS OlD F I L L E T CJSZ) THRESHOLD FOR FISH MEAL R- B R I N E : F ISH R AT I O
X · COMPOSITE O F A L L SMALL E R COD e = LARGER COD
FIG. 8 . Salt absorption in eviscerated cod stored in half-strength refrigerated sea water at 3 2 ° F.
53
... oJ « (/) ... z I&J 0 a: I&J Q.
2.4
2.2
2.0
1 .8 1 .0
0.8
0. 6
0.2
R - 0 . 5 0 + R - 0 . 5 6 + R - 0.7 1 � R - SEA WATE R : F IS H RATIO I
AVG . WT. U N EV ISCE RATE D COD
•• --... SMAL L - 3 . 5 LB
a L A R GE - 6.5 LB ( I ) R EFR IGE R ATED SEA WATER (R) F I LLE T (DD C AR C AS S
(Bl) T H R ESHOLD T O UNSU I TABI LI T Y F O R I I SH M EA L
•
2 3 4 5 6 7 8 9 10 I I 12 13 14 STORAGE TIME IN DAYS
FIG. 9. Salt absorption in u neviscerated cod stored in refrigerated sea water ( 3 % salt ) at 32 ° F.
54
percentage of salt (0 . 5 %) was reached in fillets from large gutted cod stored at 30 ° F in 5% salt RSW (Fig. 7 ) . The fish were slightly frozen which probably accounts for slow absorption of salt from the fortified RSW medium. The effect of using half strength ( 1 . 5 % salt) RSW on uptake of salt by the fish flesh and carcass is shown in Fig. 8. The rate of salt absorption was much less than the rate associated with the use of 3 % salt RSW. Figure 9 shows salt absorption with time when ungutted cod were held in 3% salt RSW. In this instance also , the rate of absorption was reduced over that associated with gutted fish .
Generally, the carcasses of gutted cod which had been stored for 1 to 2 days in 1 . 5 and 3% RSW at 32°F or in 5% RSW at 30°F acquired a salt content slightly exceeding the threshold value (0 . 5%) that would be considered an upper limit of suitability for use of the carcasses as fishmeal offal . A 0 . 5% salt content in the offal would result in a salt content of about 2 . 5 % in the dry meal . With ungutted cod, storage could be extended to 4 days. I f offal from RSW stored cod is to be used in the production of fish meal , the question of excess salt could pose a serious problem.
eTe IN FISH PRESERVATION
In the RS\V storage medium when no eTe was added , a characteristic foul odour developed after about 7 days storage at 3 2 ° F . As stated previously , this seaweedy, sharp odour easily distinguishes RSW-held cod from iced cod . The incorporation of eTe into the medium considerably reduced this odour development. The eTe dip treatment of gutted cod reduced the extent of normal "souring" characteristic of extended storage in ice.
The viable bacterial count of the liquid media at 5 days in a typical experiment showed 2 . 6 7 X 1 06 for the ice melt , and 0 . 83 X 1 06 for the RSW (with no erc added) . In another experiment , the count was 1 . 06 X 1 06 for the iced , and 0 . 07 X 1 06 for the RSW ( 1 0 ppm eTe) for about the same time. Thus the RSW with no eTC showed a lower count than the ice melt , and an even lower count was found when ere was added to the RS\V medium. Steiner and Tarr ( 1 9 5 5 ) reported comparable findings with immature coho salmon.
In this connection it would appear that the type of spoilage organism which developed , rather than the total count, should be considered in assessing the storage environments of RS\V-stored and iced cod .
Table V shows : (a) a decrease of CTe concentration in the RSvV medium but an increase in both the skin and fillet of gutted cod with storage , and (b) a decrease of CTe in the skin and fillet of CTC-dipped iced cod . I t appears that the CTC in the RSW-stored fish increased while the CTC in the eTC-dipped
fish decreased with time.
From the standpoint of fish preservation , the combination CTC-dipped-iced treatment would therefore appear to be the most desirable method for the
preservation of fresh gutted cod , since only negligible amounts of erc remained
on storage . This minute amount would in all probability be destroyed during cooking, according to the findings of Steiner and Tarr ( 1 95 6) .
55
TABLE V. Residual CTC in CTC-dipped iced cod ; in RSW-stored cod ; and in RSW mt-dium. All stored gutted cod were sprayed with fresh tap water to remove any salt or s l ime on the surfaces
of the fish before sampling for C TC determinations.
Residual CTC (ppm ) in
Storage time (days) 75 -ppm CTC-dipped, then lO-ppm RSW-stored 3 % salt RSW iced cod cod
with --------------Skin M uscle Skin Muscle 10 ppm erc
The salient points noted in connection with storage in RS\V are :
( 1 ) Taste panels could detect the presence of " salt fish" tastes in RSWstored sam pIes of cod when the flesh contained O . S % salt (correspond
ing to caught-age of S days ; ratio of RSW to fish , by weight , = 1 . 3 : 1 ) .
Tastes were found t o b e obj ectionable when the level reached 0 . 9 %
(corresponding to caught-age 8 to 9 days) .
( 2 ) Bad flavours were more prevalent in RSW than in iced samples. These
may be minimized to some extent by using CTC in the RSW medium
or by lowering the temperature of that medium to 30°F.
(3 ) RSW-stored fish and the fillets cut from them may have a distinctive sharp seaweedy or rancid odour after storage of 7 days or more in the
RS\V medium. This parallels the development of obj ectionable flavours and high salt con ten t in the fish flesh .
(4) RSW-stored and iced cod may be identified at a comparatively early caught-age . One or both eyes of RSW-stored cod may become opaque
at a caught-age of 1 or 2 days while those of well-iced fish will be com
paratively clear. At 4 days caught-age RSW-stored cod tend to have
bleached gills in contrast to the somewhat reddish gills of iced fish .
About this time , one notes a characteristic seaweedy odour from RSW
stored cod which develops at about 7 days into sharp seaweedy , rancid
odours. At 7 days iced cod may be starting to develop pronounced
characteristic "sour" odours.
(S) In regard to general appearance (other than the appearance of the eyes) , and in firmness and absence of indentations in the flesh , RSW-stored
cod look more appealing than iced cod , at least until the fish have reached
7 days caught-age.
S6
(6) It would be necessary to know the extent of public acceptance of RSWstored cod used for the production of fish fil lets and fish blocks. Salt content of the fillet has a direct bearing on acceptability, and salt , in the role of a catalyst , may play a significant part in the development in the flesh of rancid and "salt fish" flavours.
Our present knowledge would suggest that RSW could play a role in the preservation of shore-caught cod if facil ities provided a uniform holding temperature of 32° F or lower and the fish were not held more than 2 or 3 days. However, more should be known concerning the role of salt in accelerating the rate of decomposition of cod l ipids associated with known conditions and periods of frozen storage . Only then could definite recommendations be made concerning the advisability of using a RSW holding medinm for cod intended for subsequent freezing and storage . A short storage period in RSW under good conditions would probably not affect the suitabil ity of cod for canning. The RSW method could have the advantage of : (a) ease of stowage and of discharge from storage , (b) an improved stowing rate , and (c) avoidance of crushing.
The effect of salt penetration already mentioned would be a possible l imiting factor in the use of RS\V on the Atlantic trawler where caught-age of landed fish may be 7 to 8 days or even longer. An RSW method would have to be flexible enough to permit storage of all species normally landed . The keeping time of d ifferent species in RSW would have to be known and costs of handling the individual species in RSW determined . The presence of relatively large amoun ts of salt in RSW-stored fish , parts of which are normally used in the production of fish meal , would be a limiting factor in the overal l economy of the fishing operation .
At the present time , i t should be much less costly to use on trawler catches a CTC dip followed by icing. A superior landed quality should be obtained in this way.
ACKNOWLEDGM ENTS
The authors gratefully acknowledge the assistance of various members of the Board ' s Halifax Station staff in organizing, and analyzing the results of, the taste panels. The late Mr. A . S . MacFarlane , while Chief of the Department of Fisheries Inspection Branch , Halifax , assisted in carrying out assessments of the raw cod before and after filleting.
5 7
REFERENCES
CASTELL, C. H . , MAXINE F. GREENOUGH, R. S. RODGERS AND A. S. MACFARLANE. Grading fish for quality. 1 . Trimethylamine values of fillets cut from graded fish. Res. Ed. Canada, 1 5 : 701-7 1 6 .
1958. J. Fish.
CASTELL. C. H . , MAXINE F. ELSON AND JACQUELINE G. GILES. 1 96 1 . Grading fish for quality. 4. Variations in the relation between trimethylamine values and grades for gutted , trawler-caught Atlantic cod and haddock. J. Fish. Res. Ed. Canada, 18 : 303-3 1 0 .
COHEN, EDWARD H . , AND JOHN A. PETERS. 1 96 1 . Storage o f Fish in Refrigerated Sea \Vater. U.S . Fish & Wildlife Service, Gloucester Laboratory, Gloucester, Mass. U .S .A . A paper presented at the 5th Atlantic Fisheries Technological Conference , February 1 9-22 , 196 1 , Williamsburg, Va. , U.S .A.
DYER, W. J . , AND F. E . DYER. 1947 . Losses through leaching by water from melting ice of soluble constituents in iced, gutted cod. Fish. Res. Ed. Canada Prog. Rept. A tlantic Coast Sta . , No. 40, pp. 3-5.
DYER, F . E., AND W. J. DYER. 1 949. Res. Ed. Canada, 7: 449-460.
Changes i n the palatability of cod fillets. J. Fish.
FRASER, D. 1 . , A. MANNAN AND W. J. DYER. 1 96 1 . Proximate composition of Canadian Atlantic fish . 3 . Sectional differences in the flesh of some miscellaneous teleosts, chondrostei and Holocephali . J. Fish. Res. Ed. Canada. ( I n press . )
LILJEMARK, A. 1 959 . Arsredog6relse ( July 1 , 1 959 , to 30 June, 1 960) page 46. Svenska I nstitutet for Konserveringsforskning, G6teborg, Sweden .
REAY, G. A . 1 9 5 7 . Report o f the Superintendent o f the Torry Research Station and the Humber Laboratory for 1957 . Dept. Sci. I ndustr. Res . , London, Food I nvestig. Bd . Rept . , p . 6 .
REAY, G. A. 1958 . Report of the Director of the Torry Research Station for 1958 . Dept. Sci . I ndustr. Res . , London, pp. 5-6.
STEINER, G. , AND H. L . A. TARR . 1955 . Transport and storage of fish in refrigerated sea water. I I . Bacterial spoilage of blueback salmon in refrigerated sea water and in ice, with and withont added chlortetracycline . Fish. Res. Ed. Canada Prog. Rept. Pacific Coast Sta . , 1\' 0 . 104, pp . 7-9 .
STEINER, G. , AKD H . L . . \. TARR. 1956 . Penetration of chlortetracyline into flsh muscle and its destruction by heat. Canadian J. Technology, 34 : 2 1 5-2 19 .
58
APPEN D I X I I
CHI LLED WATER FO R THE PRESERVATION O F FRESHWATER FISH
By A . W. LANTZ
Fisheries Research Board oj Canada
Technological Unit , London, Ont o
Since the main portion of this Bulletin deals with experiments and applications of the sea water system of chilling and holding marine fish on the Pacific Coast, and Appendix I deals with similar work on the Atlantic Coast, involving also marine fishes , it was deemed desirable to include in this Appendix a report on some experiments at this Unit to assess the usefulness of an analogous application of mechanically chilled fresh water system in some freshwater fisheries operations . Experiments were initiated early in 1 95 7 . This work is described in an article already published (Lantz , 1 959) but for convenience and completeness , the main points will be repeated here .
Three portable tanks of capacity 3 0 cubic feet each and equipped with immersion-type refrigeration units were secured for these experiments on shortterm holding of Lake Erie fishes such as smelt , perch , and yellow pickerel . Each " package" refrigeration unit consists of a compressor, condenser and evaporator, as well as a built- in agitator, and weighs 85 lb . Later , a larger tank with capacity of 40 cubic feet served by a more powerful refrigeration unit was installed (Fig. 1 ) .
FIG. 1 . Portable tank o f chilled water with "package" immersion-type refrigeration unit.
59
Due to the nature of the local (well) water supply, it has been necessary to replace the tank liners with similar liners of an aluminium alloy of a type which is resistant to salt water. D uring 1959 , modifications were made to the " package" refrigeration units to improve water circulation and thus improve heat transfer from the water to the evaporator.
The portable chill tanks with the refrigeration units can be transported on a t-ton delivery truck to facilitate handling during transport between the laboratories and fishing craft , processing plants, etc . , and propane-operated generators
for use with the "package" refrigeration units can be used safely aboard the
fishing vessel .
The experiments and tests conducted so far indicate that freshwater fish
can be chilled and held for such periods that are normally involved in the catchervessel transporting fish from the nets to the plant. Early experiments were con
ducted with a mild brine to simulate sea water , and while in most cases the fish
chilled and held in such a brine were superior to "control " fish held in ice for the
same length of time , for short holding periods the difference was insignificant
when the icing was carefully done.
Since the holding of fish in melting ice proved efficacious for relatively short
periods , i t seemed worthwhile to determine the effect of chilling fish in the
refrigerated tank employing fresh water held at a temperature as close to its
freezing point (32°F) as practicable . :0J Ul11erous experiments were carried out
under such conditiolls , with complete success . In some cases , fish that came out
of nets alive remained alive in the chilled fresh water until they arrived at the
plant , and as a result this technique is being favoured.
FIG. 2 . Yellow pickerel fro111 the portable chill tank.
60
Figure 2 shows fish that were transported in a chill tank employing fresh water.
The economics of the chill tank system have not been worked out for freshwater fish operations, but the reactions of those fishermen who have collaborated in various experiments indicate that it may be practical for lake boats , as well as for other applications in freshwater fisheries operations.
REFERENCES
LANTZ, A. W. 1959 . Refrigeration equipment applied in the mechanical chilling of fish during transport. Fisheries Research B oard of Canada Frog. Rept. BioI. Sta. and Technol. Unit, London, Ontario, No. 1 , 38-40.
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