Koiller 1985 Aquacultural-Engineering

7/28/2019 Koiller 1985 Aquacultural-Engineering

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Aqu acu l t u ra l Eng i neer ing 4 (1985) 235-246

A L a b o r a t o r y S c a l e R e c y c li n g W a t e r U n i t f o r T i la p i aB r e e d i n gM. Koi l ler and R.R . Avtal ion

Department of Life Sciences, Bar-Ilan University, Ramat-Gan 52 100, Israel

A B S T R A C TThe t echn i ca l f ea t ure s o f a l abora t ory s ca le w a t e r r ecyc l ing u n i t f o r e xper i-m enta l sm al l scale t ilapia b reeding are descr ibed . Tw o un i t s (1 and 2) wereopera t ed dur i ng a 6 m o n t h pe r i od , car ry ing a s im i l a r f i sh l oad ( 7 . 5 kg ) andfeed ing ra te (2% f i sh bo dy weight~c lay). Un i t 1 rece ived natural i l lumina-t ion , w hi le un i t 2 was ar t if i c ia l l y i l lumin ated (1 4/1 0 - l ight /da rk cyc le ) .Bo t h un i t s w ere equ i pp ed wi t h a b i o log i ca l f i l te r bed ( subs tra t e sur facearea, 350 0 e ra2 ). I n un i t 1 , t o t a l am m on i um and n i t r i t e concen t ra t ionsr a n ge d f r o m 0 . 0 5 t o 0 . 5 m g l i te r a , w h i l e n i tr a te v a rie d b e t w e e n l O - 4 0 m gl i te r ~. I n un i t 2 cor re spond i ng values were 0 . 15 - 3 m g l i te r 1 , 0 . 05 - 0 . 8 m gl it e r ~ and 10 - 4 0 rag l it e r ~ . Tem pera t ures ranged b e t ween 20 - 29 C andpH values be t wee n 7 . 5 - 6 . 9 i n bo t h un i t s . D i s so lved oxyg en concen t ra t ionsdecreased gradua ll y f rom 5 . 6 t o 3 . 4 m g li te r ~ i n un i t 1 and f rom 5 . 6 t o2 . 6 m g l i t e r 1 i n u n i t 2 . Tw en t y - s i x spawn i ngs occur red i n un i t 1 i n M archand A pr i l , wh i l e on l y e i gh t spawn i ngs occur red i n un i t 2 , pos s i b l y becauseo f the absence o f sunl ight . The s igni f icance o f these resul t s are d iscussed .

INTRODUCTIONThe continuous elimination of toxic metabolites and growth-inhibitingsubstances is an essential process when operating a closed system forintensive fish culture. Many recycling water systems using biologicalfilters have been used for the degradation of accumulative organiccompounds which originate from fish excretion and excessive feed(reviewed by Otte and Rosenthal, 1979). However, biological filtrationhas some disadvantages, in particular, the accumulation of nitrate (theend-product of nitrification) and low-biodegradable substances. To

235Aquaeu l t u ra l Eng i neer i ng 0144-8609/85/$03.30 - Elsevier Applied SciencePublishers Ltd, England, 1985. Printed in Great Britain


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236 M. Koiller, R. R. Avtalioncope with this problem a certain amount of water must be continuouslyreplaced or the recirculated water treated accordingly (i.e. anaerobicdenitrification, activated charcoal, ozonation). A further disadvantageof biological filters is their slow adaptability to environmental variations,such as changes in temperature, salinity, dissolved oxygen, organicwaste load and fish biomass (Coldberg and Lingg, 1978; Otte andRosenthal, 1979). Nevertheless, when operating small closed systemsfor fish breeding on a laboratory scale, it seems reasonable to employbiological filters and to change the water partially, whenever necessary,rather tha n to treat it chemically (chemical filtration devices, ozona-tion, etc.).The accumulation of organic residues and the harmful effects ofthese residues on fish growth is one of the main problems of intensiveaquaculture. The sedimentation of organic matter in fish ponds resultsin anaerobic conditions and the production of toxic materials such asNH4, H2S, etc. The continuous aeration and resuspension of organicmatter was reported to enhance the recycling of the organic matterin fish ponds (Avnimelech and Lacher, 1980; Shilo and Rimon, 1982).Similar processes occur in biological gravel beds. The accumulationof heavy detritus (particulate matter) in the gravel bed increases thebiological oxygen demand (BOD) of the system and reduces its carryingcapacity. Hence, excessive detritus must be removed periodically(Spotte, 1979).

In this article we describe a laboratory scale recycling unit for experi-mental breeding of tilapias. This unit is equipped with a biologicalgravel-bed filter capable o f avoiding excessive accumula tion of detritusand thus avoids supporting effective nitrification.

MATERIALS AND METHODSThe recirculation unit consisted of four aquaria and an externalbiofilter (see Fig. 1).

Aquaria of 250 liters (169 X 38 X 39 cm) provided space for a familyof tilapia composed of 2 males and 4-6 females. (Each aquarium had7-8 fish with an individual average weight of 250g, totalling 1875 gof fish. The average individual fish length was 25 cm.) Two separatenesting zones were established by the 2 males in the corners of theaquaria. Aquaria consisted of a skeleton of fiberglass to which the walls


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A laboratory scale recyc l ing wate r uni t for t ilap ia breeding 237

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bed; OV , overf low ; OVF , f i lter ove rf low; P, pum p; ST, aquaria s tand; T, tap.


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2 3 8 M. Koiller, R. R. Avtalionand the bottom plate were glued. The front wall was made of glass(8 mm thick), while the bottom and the rest of the walls were made ofasbestos (8 mm thick). The level of the wa ter (33 cm) in each aquariumwas maintained by an overflow outlet, from which the collected excesswater was piped into the biofilter bottom.

The biofilter (70 50 40 cm) and its components are depicted inFig. 2. Waste water from aquaria flows through a PVC collecting pipe(5 cm diameter) into the sediment settling space (see Fig. 2) where thefirst stage of filtration occurs. Since the filtration process proceedsfrom the bottom to the top (upflow speed 1-14 cm min-1), heavierparticulate mat ter precipitates when the water in the sediment settlingspace flows upwards through the gravel bed where the biological filtra-tion takes place. The filtered water is recirculated to aquaria by a sub-merged centrifugal pump (Eheim Filter & Fish Co., Germany). Thelevel of the water in the biofilter is maintained by a float valve. When acomplete or partially open system is operated, the excess water flowsthrough the overflow to the sewage. The first stage of filtration repre-sents a significant reduction step of the organic load, since accumula tedsuspended solids are evacuated to the sewage at desired intervals using aprogrammed automatic tap (solenoid valve). A mechanical tap was

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A laboratory scale recyc l ing wa ter uni t fo r t i lap ia breeding 239

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Fig . 3 . Th e grave l bed . 1 , s edim ent se t t l ing space ; 2 , PVC f i l t er p late supp or ters ;3 , f i l t er p l a t e ; 4 , P V C n e t o f 3 m m m e s h s i z e ; 5 , p or ou s gr ave l; 6 , n y l on n e t o f0 - 8 mm me s h s i z e ; 7 , d o l omi t e gr ave l .

f i x e d b e f o r e t h e s o l e n o i d v a lv e t o p e r m i t m a n u a l e v a c u a t i o n . T h is s y s t e m ,b e s i d e s p e r m i t t i n g t h e r e p l a c e m e n t o f w a t e r a t t h e d e s ir e d r a te s , a ls oa l l o w s s e l f- c l e a n in g o f t h e f i lt e r a n d a v o i d s it s o v e r l o a d i n g s i n c e , d u r i n gt h e e v a c u a t i o n t i m e t h e f i lt e r b e d i s s u b j e c t e d t o a r e v e r s e - f l o w .

T h e g r a v e l b e d a n d c o m p o n e n t s a r e i l lu s t r a t e d i n F i g . 3 . T h e g r a v e lb e d is c o m p o s e d o f t w o l a y e rs o f g ra v e l s e p a r a t e d b y n e t s. T h e f i rs tl a y e r , 5 c m t h i c k , c o n s i s t s o f d o l o m i t e g r a v e l o f 2 - 5 m m g r a in s i ze , w i t ha v o i d s p a c e o f 3 6 0 m l l it e r -1 -+ 0 . 8 3 a n d a n i n n e r s u r f a c e o f 5 7 6 0 m 2m -3 + 2 - 3 2 . ( T o s i m p l i f y t h e i n n e r s u r f a c e c a l c u l a t i o n , t h e g r a v el w a sa s s u m e d t o b e s p h e r i c a l . ) T h e s e c o n d l a y e r 4 c m t h i c k , c o n s i s ts o f ap o r o u s g r av el ( E f f i s u b s t r a te - E h e i m F i l t e r & F i s h C o ., G e r m a n y ) o f5 m m g r a i n s i z e , w i t h a v o i d s p a c e o f 5 3 8 . 6 m l l i te r -1 -+ 0 . 5 3 , t h u s o f f e r -i ng a n i d e a l a n d e x t e n d e d a d h e s i o n s u r f a c e f o r b a c t e r i a . T h i s l a y e r isc o m p l e t e l y i s o la t e d f r o m t h e s e c o n d o n e , s in c e i t is e n v e l o p e d b y aw h i t e n y l o n n e t o f 0 . 8 m m m e s h s iz e t h a t a ls o m e c h a n i c a l l y f i l t ra t e st h e w a t e r . H o w e v e r , t h e i n n e r s u r f a c e o f t h is p o r o u s g r av e l, u n d o u b t e d l y


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240 M. Koiller, R. R. A vtalionm u c h m o r e e x t e n d e d t h a n t h e d o l o m i t e g r a v el , is d i f f ic u l t t o c a lc u l a te .A 3 - m m m e s h n e t s e p a r a t e s t h e d o l o m i t e g r av e l f r o m t h e w h i t e n e t .T h e d o l o m i t e g r a v e l [ C a M g ( C O 3 ) ]2 a c t s a s a n a t u r a l b u f f e r i n t h e w a t e rs y s t e m s i n c e i t c o n t a i n s a l ar g e s o u r c e o f c a r b o n a t e s t o n e u t r a l iz e t h ea c i d - f o r m i n g p r o c e s s e s o f c l o s e d c u lt u r in g s y s t e m s ( S p o t t e , 1 9 7 9 ) . T h eg r av e l b e d w i t h t h e f i l t r a t io n e l e m e n t s c a n e a si ly b e d i s m o u n t e d .

R e c i r c u l a t i o n o f w a t e r is d e s c r i b e d i n F i g s 1 a n d 2 . A t a p ( T ) w a sc o n n e c t e d t o a p ip e ( 1 - 2 7 c m d i a m e t e r ) t o a l lo w f r e e f lo w o f t h er e c i r c u l a te d w a t e r , a v o i d in g h e a d l os s o f t h e p u m p . F o u r t a p s w e r ec o n n e c t e d t o t hi s p i p e t o s u p p l y th e r e c i r c u l a te d w a t e r t o e a c h a q u a r i u m .A t a p w a s c o n n e c t e d t o t h e s y s t e m t o p r o v i d e w a t e r f r o m a n e x t e r n a ls o u r c e . I f a p a r t ia l ly o p e n s y s t e m is d e s i re d ( e. g. a m o u n t s o f w a t e re q u i v a l e n t t o 2 0 - 3 0 % d a y -1 o f t h e t o t a l r e c i r c u l a te d w a t e r i n th e c l o s e ds y s t e m ) , t h is t a p is r e g u l a t e d t o s u p p l y w a t e r . I t i s a l s o p o s s i b l e t oo p e r a t e a c o m p l e t e l y o p e n s y s t e m f o r s o m e h o u r s b y o p e n i n g th ee x t e r n a l w a t e r s o u r c e t a p . I n t h a t c a e , t h e ta p ( T ) m u s t b e c l o s e d t op r e v e n t w a t e r f l o w i n g t o w a r d s t h e b i o f i l te r . I n a d d i t i o n , t h e b io f i l t e rs e w a g e t a p a n d t h e s o l e n o i d v a l ve m u s t b e o p e n e d . I n t h a t w a y , t h ew a s t e w a t e r e n t e r i n g t h e b i o f i l te r , i n s te a d o f f lo w i n g u p w a r d s t h r o u g ht h e g r av e l b e d a n d f il te r o v e r f l o w , w o u l d f l o w d i re c t l y f r o m t h e s ed i-m e n t s e t t li n g s p a c e t o t h e d r a i n s y s t e m . T h e c e n tr if u g a l p u m p w a sr e g u l a t e d t o c i r c u l a t e t h e w a t e r a t a r a t e o f 4 l i t e r m i n -1 (1 l i te r m i n -~i n f l o w r a te t o e a c h a q u a r i u m ) . S i n c e t h e v o i d s p a c e o f t h e b i o f i l t e rg r a v e l b e d e q u a l s 1 3 - 8 4 l it e rs , t h e r e t e n t i o n t i m e o f t h e w a t e r in t h eb i o f i l t e r c a n b e e v a l u a t e d t o 3 .5 m i n . R e c i r c u l a t i o n o c c u r r e d e v e r y4 h , a l lo w i n g a t h e o r e t i c a l t u r n o v e r o f 6 t i m e s d a y -~ .

A e r a t i o n t o a q u a r i a w a s s u p p l i e d b y a i r d i f f u s e r s a n d a i r s t o n e s ( se eF i g. 4 ). T h e d i f f u s e r ( E h e i m F i l te r & F i s h C o . , G e r m a n y ) w a s f i t te d a tt h e e n d o f th e i n le t h o s e o n t h e w a t e r ' s s u r fa c e a n d a t t a c h e d t o t h ea q u a r i u m w a l l ( s p r a y a n g le a b o u t 4 5 ) . T h e a i r - h os e o f t h e d i f f u s e r ist a k e n u p w a r d s t o a p o i n t o u t s i d e t h e a q u a r iu m . T h e d i f fu s e r u n it m i x e st h e s u p p l i e d a ir w i t h t h e i n c o m i n g w a t e r , w h i c h is s p r a y e d a s a re s u lt o ft h e p r e s su r e o f t h e w a t e r . T h i s e n s u r e s o x y g e n a t i o n o f t h e w a t e r a n de n a b l e s s u r f a c e a g i t a t i o n , a n i m p o r t a n t f a c t o r f o r d i f f u s io n o f o x y g e na c r o s s t h e a i r - w a t e r i n t e r f a c e . T h e d i f f u s e r p ro v i d e s a g o o d i n d i c a ti o no f t h e f l o w r a te o f t h e s y s t e m . W h e n th e p u m p o r th e t a p s a re b l o c k e dw i t h p a r t ic l e s o f m a t t e r , t h e r e d u c e d w a t e r p re s s u re r e d u c e s th eq u a n t i t y o f a ir s p r a y e d b y t h e d i f fu s e r . I n c a se o f p u m p f a i lu r e , t h ed i f f u s e r w o u l d n o t w o r k . S i m u l t a n e o u s l y , a c o n t i n u o u s a e r a t i o n t o


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A laborato ry scale recy c l ing wa ter uni t for t ilap ia breedingHose

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a q u a r i a is s u p p l i e d b y a c o m p r e s s o r t h r o u g h a s e p a r a t e p i p e ( s e e F i g . 1)c o n n e c t e d t o an a i r ta p a n d a i rs to n e . T h e w a t e r t e m p e r a t u r e ( 2 6 - 2 8 C )is m a i n t a i n e d b y t h e r m o s t a t i c a l l y c o n t r o l l e d i m m e r s i o n h e a t e rs .

T h e f e e d i n g r a t e w a s e s t a b li s h e d a s 2 % o f th e a v e r a g e b o d y w e i g h t o ft h e f is h e s d a y -x , b u t d u r in g e x p e r i m e n t a t i o n a n a t t e m p t w a s m a d e t oi n c re a s e t h is p e r c e n t a g e . T h e f is h w e r e f e d w i t h c o m m e r c i a l t r o u t p e l le t sc o n t a i n i n g 4 2 % p r o t e i n s , 1 2 % li p id s , 2 0 % w h e a t f l o u r , 1 % v i t a m i n s a n d2 % c e l l u l o s e .

T h e w a t e r q u a l i t y m e a s u r e m e n t s w e r e t a k e n w i t h o u t t h e o p e r a t i o no f t h e s o l e n o i d v a l v e a t a 1 l i te r m i n -1 f l o w r a t e t o e a c h a q u a r i u m a n dt h e m e c h a n i c a l t a p w a s o p e n e d o n c e a d a y t o re p l ac e a b o u t 1 0% o fw a t e r c o n t e n t o f t h e b i o f i l t e r c o n t a in e r . M e a s u r e m e n t s o f t e m p e r a t u r e ,p H , d i s s o lv e d o x y g e n , a m m o n i a , n i tr i te a n d n i t ra t e w e r e t e s te d . T h e s ed e t e r m i n a t i o n s w e r e c a r ri e d o u t u s in g t h e m e t h o d o l o g y d e s c r i b e d in t h el i t e r a t u r e ( T a r a s e t a l . , 1 9 7 1 ; B o y d , 1 9 7 9 ) .

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W a t e r s a m p l e s f o r q u a l i t y d e t e r m i n a t i o n s w e r e i n i ti al ly t a k e n i n t w oi n d e p e n d e n t u n i ts ( u n i ts 1 a n d 2 ) , o n c e p e r w e e k , u s u a l l y b e f o r e f e e d -


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242 M. Koiller, R. R. Avtalioning (during morning hours). Unit 1 was installed in a place where theroof was partially transparent and near large windows allowing strongnatural illumination and heat (essential factors for the spawning processin tilapias), Unit 2 was artificially illuminated by fluorescent lighting(14/10- light/dark cyele). Both units began operating in December,1982. The determina tions are shown in Figs 5 and 6.

Temperatures in units 1 and 2 varied between 20-29C and 20-28C,respectively. These variations were more pronounced in winter becauseof the sharp shifts in environmental temperature and the insufficiencyof the heaters used to provide the desired tempera tures during thecolder days.

Dissolved oxygen levels of the filtered water decreased from 5-6 to3.4 mg liter 1 in unit 1, and 5.6 to 2.6 mg liter-1 in unit 2, probably dueto the oxygen consumption o f microorganisms decomposing organicmatte r in the gravel bed. In addition, heavy detritus covering the gravelbed (especially noted in unit 2) and accumulative organic load in theculture system, offered additional substrate for bacterial growth andconsumption of dissolved oxygen. Furthermore, the level of dissolvedoxygen decreased when the pump or the taps and diffusers were partiallyblocked by particulate matter.

The pH values decreased gradually with time, varying between 7.5-6.9. This decrease is the result of alkalinity-loss during nitrificationand oxidation of organic waste products by bacteria. However, thepartial water replacements neutralized such decreases. It is possible tha tthe dolomite gravel contributed to the gradual decline of the pH.

Total ammonium concentrations in unit 1 ranged between 0.05-0-5mg liter x and heavy detritus covering the gravel bed was not observedas in unit 2. In unit 2, ammonium values were kept between 0.15-1 mgliter-1, but at the end of the experiment a sudden increase (up to 3 mgliter ~) was observed. Even though water was changed, total ammoniumlevels continued to rise. This unusual increase of ammonium can pos-sibly be explained by a significant reduction of the oxidative capacityof nitrifying bacteria in the gravel bed, due to the interspecific competi-tion with heterotrophic bacteria. For both units, the low pH valuesassured that unionized ammonia was present at very low levels, beingharmless to the cultu red fish.

Nitrite and nitrate values in unit 2 varied from 0-05 to 0.8 mg liter ~and 10 to 40 mg liter-x, respectively, while in unit 1 they were 0.05 to0.5 mg liter-1, and 10 to 40 mg liter-1, respectively.


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10/12

244 M. Koiller, R. R. AvtalionDISCUSSION

The concentrati on of total a mmon ium ions increased with time, accom-panied by nitrite and nitrate increases in both units, indicating someincomplete nitrification. In unit 2, ammonium and nitrite reachedmaximum levels (1 mg liter 1 and 0.8 mg liter 1, respectively) afteralmost 9 weeks without water replacements. This can largely be attri-buted to the fact that the biofilter was covered with excessive detritussupporting hete rotrophic bacteria. The aquarium water presented a verystrong yellow color, indicating the accumulation of yellow substancesand other low-degradable organisms. The activity of fish was reducedand one case of death occurred. In unit 1, however, both a mmoniumand nitrite values on ly reached 0.5 mg liter-1. The filter was slightlycovered by detritus, the fish activity was normal and no mortal ity wasexperienced. It is possible that the low-degradable substances in con-nection with lowered oxygen (unit 2) may have affected the fish ratherthan nitrite alone at the concentration of 0-8 mg liter-a. It is alsopossible that nitrite toxici ty was enhanced as a result of the combinedeffects with the other accumulated metabolites.

In both systems the increases in temperature generally coincidedwith the increase of metabolite. This shows, that metabolic excretionand activity increased faster with temperature rise than the biofilteractivity. Fish breeding activity was reduced at low tempera tures and,consequently, the organic load and the metaboli te levels were reduced .At 23C fish could consume more, but at 25C the feeding activity wasgreatly intensified. When the temperature varied between 25-29C, thefeeding rate was increased to 3% fish bodyweight/day 1, but some feedremained at the bottom of the aquaria. Therefore, the increasingtemperature resulted in a higher fish metabolism for which the bacterialactivity in the filter was not sufficient.

Spawnings were more intense in unit 1 due to the natural illumina-tion and the higher temperature regime (26 spawnings during Marchand April), while only eight spawnings occurred in unit 2. The partialwater replacements accelerated the spawning process and handled themetaboli tes at lower levels.

The results of the water quality determinations for both units showthat the biological filter could not handle the accumulation of meta-bolites and low-biodegradable substances (yellow color in aquaria)without water replacements, although the total bioload was relatively


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A laboratory scale recycling water unit for tilapia breeding 245l o w . A w a t e r r e p l a c e m e n t r a te o f a b o u t 5 0 % o f t h e to t a l v o lu m e o f t h eu n i t , e v e ry 3 to 4 w e e k s , w a s f o u n d t o b e s a t i s f a c t o r y .

I n o r d e r t o m a i n t a i n t h e s a m e w a t e r q u a l i t y c o n d i t i o n s t h a t p r e v a il e dd u r in g t h i s e x p e r i m e n t a n d t o a l w a y s g u a r a n t e e s u f f i c i e n t t o t a l a m m o n i ao x i d a t i o n f o r t h e t o t a l b i o m a s s l o a d o v e r l o n g e r t i m e p e r i o d s , in ap e r m a n e n t c l o s e d s y s t e m , t h e r e is a n e e d t o d e t e r m i n e t h e c a r r y in gc a p a c i t y o f t h e b i o fi l te r . H i r a y a m a ( 1 9 7 4 ) p r o p o s e d a f o r m u l a f o r t h ec a l c u l a t io n o f t h e c a r ry i n g c a p a c i t y o f a s m a ll m a r i n e s y s t e m . H o w e v e r ,t h is f o r m u l a c o u l d n o t b e a p p l i e d t o o u r s y s t e m b e c a u s e w e s ti l l c a n n o tc a l c u l a t e t h e i n n e r s u r f a c e o f a p o r o u s g ra v e l, w h i c h m a y e n la r g e th es u r fa c e f i lt r a ti o n a r e a fo r b a c t e r ia l a t t a c h m e n t . H i r a y a m a s t a t e d t h a ti n h is m e t h o d o f e s t im a t i n g c a r r y i n g c a p a c i t y , t h e w a t e r p u r i f ic a -t i o n w a s a s s u m e d t o o c c u r o n l y o n t h e s u r f a c e o f t h e s an d gr ai ns . Ah i g h e r f l o w r a t e ( h i g h e r t h a n 1 l it e r m i n -1 p e r a q u a r i u m ) c a n r e d u c e t h eB O D l o a d ( O t t e a n d R o s e n t h a l , 1 9 7 9 ) as c a n m a i n t a i n in g t h e f e e d i n gr a t e a t o n l y 2 % d a y -1. T h i s w i ll p o s s i b l y i m p r o v e t h e p e r f o r m a n c e o ft h e b i o f i l t e r .

A C K N O W L E D G E M E N T ST h is w o r k h a s b e e n s u p p o r t e d b y g r a n t 0 3 . 5 0 9 f r o m T h e R e s e a r c h an dD e v e l o p m e n t C o . L t d , B a r - Il a n U n i v e r s it y , a n d b y g r a n t A Q 2 4 f ro mt h e G K S S , G e s s t h e c h t - T e s p e r h u d e , F R G . W e a r e s i n c e re l y g r a t e fu l t oD r H a r a ld R o s e n t h a l , o f th e B i o lo g is c h e A n s t a l t H e l g o l a n d , H a m b u r g -B a h r e n f e l d , F R G , f o r h is a d v i c e a n d h e l p i n e d i ti n g t h is m a n u s c r i p t .

R E F E R E N C E SAvnimelech, Y. & Lacher, M . (1980 ). On the role o f soi l in the maintenance of f ish

pond 's fer t il i ty in dev elopme nt of hydrobiology . In : Development in Hydro-biology, vol. 2, eds J. Barica and L. R. Mur, Jun k P ubl ., Holland.Boyd, C. E. (1979) . Water qual i ty in warm water f i sh ponds. Auburn Universi ty

Experimental Stat ion , Dep t of Fisheries and Allied Aq uac ulture, Aubu rn Univer-s i ty , Alabama, pp. 201 -76 .Coldberg, P. J. & L ingg, A. J. (1 978 ). Effe ct of ozona tion on microbial f ish patho-gens, amm onia, ni trate, ni tr i te, and BOD in simulated reuse hatc hery w ater.J. Fish. Res. Bd. Canada, 35 , 1290-6 .Hirayama, K. (1974). Water control by fi l t rat ion in closed culture systems. Aqua-culture, 4 , 3 6 9 - 8 5 .


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246 M. Koi l ler , R . R . A v ta l ionOtte, G. & Rosenthal, H. (1979). Management of a closed brackish water system

for high density fish culture by biological and chemical water treatment. A q u a -cu l tu re , 18, 169-81.

Shilo, M. & Rimon, A. (1982). Factors which affect the intensification of fishbreeding in Israel. 2. Ammonia transformation in intensive fish ponds. B a m i d g e h ,34, 101-4.

Spotte, S. (1979). Fish and Inver t ebra t e C u l tu re - Wa te r M ana gem en t i n C losedS y s t e m s , John Wiley & Sons, New York.

Taras, M. J., Greenberg, A. E., Hoak, R. D. & Rand, M. C. (Eds.) (1971). S tandardM e t h o d s f o r t h e E x a m i n a t i o n o f W a t er a n d W a s te W a t er , APHA, AWWA andWPCF Press, 13th edn, pp. 232-48.

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Koiller 1985 Aquacultural-Engineering

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