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Olesen 1983 Aquacultural-Engineering

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    Aqu acu l t ura l Eng i neer ing 2 (1983) 1-12

    A Technica l So lut ion to the M ass-cu l tu r ing o f La rva lTurbot

    J . O . O l e s e n a n d E M i n c kW ater Quali ty Insti tute, Hrsholm D K 2970, Denm ark

    A B S T R A C TA 10 00 l it re rec i rculation sy s tem o f e ight cy l indr ical rear ing tan ks has beentes ted in three 40-day per iods to de term ine i t s capa ci ty fo r rearing larvalt u r b o t (Scophthalm us maximus L.).

    The larvae were fed on rot i f ers and Artemia naup l i i , a s w e l l a s m i xe dmar i ne a l gae . C on t i nuous ar t if ic i a l l igh t o f 15 00 -20 00 l ux w as app l i ed a tthe sur face. The app l ied algae served a dual fun ct io n; kee ping rot if ers an dArtemia a t a h i gh nu t r i t i ona l l eve l as w e l l a s e f f ec t i ve l y r emov i ng t hereleased amm oni a . The co mb i na t i on o f upw e l l ing w a t er and l igh t a t thesur face m ax i m i zed t he co n t ac t sur f ace be t w e en l arvae , f o od i t ems andalgae.

    Wi th th i s sys tem , u s ing a s tockin g den s i ty o f 1 6 larvae li t re-1 in therear ing tanks , a surv ival to ta l o f 40% at D ay 40 was achieved, g iv ing aprod uc t i on o f 6 . 4 larvae l it r e -1 or 300 0 larvae me t re -2 o f t h e sur face o fthe rearing tanks.

    I N T R O D U C T I O NM u c h e f f o r t h a s b e e n e x e r t e d s i n c e t h e e a r ly 1 9 7 0 s t o d e v e l o p a n di m p r o v e t e c h n i q u e s f o r t h e m a s s - c u lt u r in g o f t u r b o t ( S c o p h t h a l m u sm a x i m u s L . ) ( S m i t h , 1 9 7 6 ; H u l l a n d E d w a r d s , 1 9 7 6 ; K i n g w e l l e t a l . ,1 9 7 7 ; B r o m l e y , 1 9 7 8 ; P e rs o n - L e R u y e t e t a l . , 1 9 7 8 ; H o w e l l , 1 9 7 9 ) .

    S o m e o f t h e o b s t a c le s t o t h e r o u t i n e c u l t u r in g o f t u r b o t o n ac o m m e r c i a l s c a le a r e t h e l ac k o f re g u l a r s u p p l i e s o f g o o d q u a l i t y e g gs

    1A q u a c u l t u r a l E n g i n e e r i n g 0 1 4 4 - 8 6 0 9 / 8 3 / 0 0 0 2 - 0 0 0 1 / $ 0 3 , 0 0 - Appl ied SciencePublishers Ltd , England, 1983. Printed in G reat Britain

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    2 J . O . O l e se n , F . M i n c k

    from captive broodstocks, difficulties in ensuring a high survival per-centages during the early larval stages, rearing from eggs of variedquality and, finally, the problem of composing sufficiently goodartificial foods for the early weaning of larvae from live foods to drypellets while maintaining a high degree of survival.

    The main purpose of the present work has been to attempt to solvethe second of these problems. This was done by testing a larval rearingsystem built on the basis of present technical knowledge combined withthe aim of improving and optimizing the physical and chemical rearingconditions in order to achieve increased survival independent of smallvariations in egg quality and viability.

    MATERIALS AND METHODSSystem descriptionFigure 1 shows the set-up of the larval rearing system. This is composedof eight cylindrical rearing tanks, four with red and four with blackPVC cylindrical lining, receiving upwelling water through conicalbottoms. The water is supplied by two submersible pumps from twointerconnected 300 litre aeration tanks: the inlet flow can be adjustedto keep the oxygen concentration at 100% saturation in the rearingtanks.

    From the rearing tanks the water returns to the aeration tanks bysurface run-off through exchangeable surface filters with mesh sizesadjusted to the size of the food items. Superimposed on each sflrfacefilter is a security filter of 0.5 mm mesh size, the function of which isto retain fish larvae inside the tanks should the surface filter becomeblocked by accumulating particulate matter resulting in a water levelrise.

    The whole system is connected to a water treatment unit consistingof a sedimentation tank, a biological filter and a sand filter.Rearing procedureFertilized eggs obtained from captive broodstocks in the UK were usedin the rearing experiments. In all cases, the eggs were incubated in

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    A technical solution to the mass-culturing of larval turbot 3

    / ~ C O N N E C T I O N T O_ _ I N L E T l l , I B I O L O G I C A L F IL T E R

    O U T L E T , ,

    -

    Fig . 1 . Larva l rear ing sys tem . A, schem at ic pres enta t ion of the rec i rcula t ionsystem wi th e ight rear ing tanks ; B , ver tica l v iew of a s ingle rear ing tank .

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    4 J . O . O l e se n , F . M i n c k

    securityfilterL I G H T : 1 S 0 0 - 2CO0uxat surface

    1 2 5 1

    j s u r facerun off~ \ outlet

    replaceablefilte r impenetrableto IrachionusorArtemie

    ~ / e n t e t i o n~=1~ ' " outlet[ ~ inlet

    F i g . 1 . - c o n t d .

    15 litre buckets in natura l sea water filtered through activated carbonand 0.22 tam cartridge filters. Temperature and salinity were graduallyadjusted to 13-5C and 33%0 S (with NaCI) irrespective of the previousincubation conditions, having ensured that the eggs and broodstockswere of oceanic origin. Fi fty I.U. m1-1 of penicillin and 0.05 mg m1-1 ofdihydros treptomy cin were added to the incubation medium to preventfungal and bacterial growth in the incubation system. Weak aerationwas applied to prevent the formation of a surface film. No watercirculation or renewal were carried out during the incubation periodwhich ended six days after fertilization with the occurrence of hatching.Up to two days after hatching the yolk sac larvae were transferredto the rearing system by gentle decantation to give a maximum stockingdensity of 16-20 larvae litre-~.

    During the first four days after transference, the temperature wasgradually raised from 13-5C to 18C in order to stimulate feedingactivity among the fish larvae. Continuous artificial light of 1500-2000 lux was applied at the surface of the rearing tanks t hroughoutthe rearing period. Salinity was adjusted to 33-34%0 and oxygen to 95-100% saturation. For the first eight days the turbot larvae were fed on

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    A technical solution to the mass-culturing of larval turbot 5rotifers (Brachionus plicatilis Mi~ller) raised on mixtures of the marinealgae Nannochloris atomus, Pavlova lutherii and lsochrysis galbana.Each day the amount of rotifers added was adjusted in order to obtaina c oncentr ati on of 3-5 rotifer s m1-1 afte r Day 2. Prior to Day 2, thecon cen tra tion was kept at 1-2 rotifers m1-1. As well as the rotifers,5 litre day -1 o f Pavlova lutherii or Isochrysisgalbana, at concentrationsof a bou t 10 million cells ml -~, were ad ded as nour ish men t for therotifers.

    Fro m Day 8, feeding with Arternia nauplii hatched from decapsulatedBrazilian cysts (BIOMAP) was started, adjusting the concentration to2-3 nauplii litre -1 once a day. Towards the end o f the rearing period (atDay 40) the concentration was reduced by grazing to less than 0.1nauplii litre-~ immediately before feeding. Together with the Artemia,0.5 litre of Tetraselmis suecica was added to each rearing tank everysecond day as food for the nauplii.

    RESULTSTable 1 presents results o f larval rearing in individual tanks fro m threedifferent periods. In trials 2, 6 and 7 losses of at least 200 larvaetowards the end of the respective periods can be accounted for bymechanical failure.

    TABLE 1Number of Larvae Successfully Reared from Different Rearing TanksPeriod Number of Durationof Surviving

    yolk sac larvae experiments larvaestocked (days)Survival

    1. Feb-Mar 1980 5 800 35 792 142. Nov-Dec 1980 1 950 42 283 153. Nov-Dec 1980 1 950 40 784 404. Nov-Dec 1980 1 950 42 774 405. Nov-Dec 1980 1 950 42 779 406. Feb-Mar 1981 2 500 45 214 97. Feb-Mar 1981 2 500 35 297 12

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    6 J.O. Olesen, F. MinekTABLE 2

    M e a n F r e s h W e i gh t o f L a r v a e F r o m a S in gle R e a r i n g T a n k D u r i n g a 3 8 - D a y P e r i o dGrowth period Number of Survival Mean larval Specific A a

    (Days) larvae fresh weight growth rateIn the From (% day -l)Start End period Day 2 Start End

    (%) (%) (mg) (mg)2 t o 7 1 950 1 950 100 100 0 .1 - -7 to 10 1 95 0 1 510 b 77 .4 77 .4 - 1 .6 -2 t o 10 1 950 1 5 t0 b 7 7 .4 77 .4 0 -1 1 .6 34 .7

    10 t o 18 1 510 b 936 62 ,0 48 .0 0 .1 - -18 t o 24 936 803 85 .8 41 .2 - 60 .1 -10 to 24 1 510 b 803 52 .3 41 .2 1 .6 60 .1 25 .924 t o 38 803 779 97 .0 3 9 .9 60 .1 164 .2 7 .2

    2 t o 38 1 950 779 39 .9 39 .9 0 ,1 164 .2 20 .61 w t

    a Spec i f i c A g row th r a t e : k = - i n - -t w o

    where t = t ime i n days , Wo --- we t we igh t o f f ish a t s t a r t and wt = w e t w e i g h t o f fi sha t D a y t .b E s t i m a t e d f r o m a c o ll e c t io n o f d e a d la r v ae b e t w e e n D a y 7 a n d D a y 1 8.

    T a b l e 2 p r e s e n t s t h e g r o w t h a n d s u r v iv a l o f l a r v ae f r o m a s in g ler e a r i n g t a n k w h i c h w a s r e p r e s e n t a t i v e o f t h e p e r f o r m a n c e o f t h e r e a r in gt a n k s w i t h t h e h i g h e s t s u r v iv a l a s s h o w n i n T a b l e 1 . T h e s p e c i f i c g r o w t hr a t e f o r t h e f i rs t 3 6 d a y s is 2 0 - 6 % d a y -~ w i t h g r o w t h r a t e s o f 3 4 . 7 %d a y -a f r o m D a y 0 t o D a y 8 , 2 5 - 9 % d a y -~ f r o m D a y 9 t o D a y 2 2 a n d7 . 2 % d a y - a f r o m D a y 2 3 t o D a y 3 6 .

    D I S C U S S I O NT h e r e s u l t s o f t h e p r e s e n t w o r k i n d i c a t e t h a t t h e r e a r i n g s y s t e m t e s t e dh a s a h i gh c a p a c i t y f o r g o o d g r o w t h a n d s u r v iv a l o f t u r b o t l a rv a e d u r i n gt h e i r f i r s t m o n t h o f l if e . I t i s b e l i e v e d t h a t t h e h i g h c a p a c i t y o f t h e s er e a r i n g t a n k s is a t t r i b u t a b l e t o t h e s y n e r g i s t ic e f f e c t s o f a n u m b e r o ff a c t o r s w h i c h t e n d t o o p t i m i z e t h e p h y s i c a l a n d c h e m i c a l c o n d i t i o n si n t h e t a n k s . T h e a d d i t i o n o f a l g ae w i t h Brachionus a n d Artemia s e r v e sa d u a l f u n c t i o n .

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    A technical solution to the mass-culturing o f larval turbo t 7

    F i r st , it h as b e e n s h o w n t h a t t h e f a t t y a c id c o m p o s i t i o n o f B r a c h i o n usr e f l e c t s a c c u r a t e l y t h e f a t t y a c id c o n t e n t o f i ts p r e y it e m s ( S c o t t a n dB a y n e s , 1 9 7 8; S c o t t a n d M i d d l e t o n , 1 9 7 9 ). F u r t h e r , as i t is k n o w n t h a tt h e f a t t y a c id c o m p o s i t i o n o f t h e f o o d o f tu r b o t is d e c is iv e f o r t h e i rn o r m a l d e v e l o p m e n t ( C o w e y e t a l . , 1 9 7 6 ; G a t e s o u p e e t a l . , 1 9 7 7 a , b ;S c o t t a n d M i d d l e t o n , 1 9 7 9 ), t h e s i g n if i ca n c e o f k e e p i n g B r a c h i o n u s ing o o d n u t r i t i o n a l c o n d i t i o n i s o b v io u s . T h e i m p o r t a n c e o f a d d in g a lg a et o t h e l i v e f o o d a l s o a p p l i e s f o r A r t e m i a . I t h a s b e e n s h o w n t h a t t h en u t r i t i o n a l v a l u e o f A r t e m i a n a u p l i i d e c l i n e s r a p i d l y 3 6 h o u r s a f t e rh a t c h i n g , as t h e a n i m a l s d r a i n t h e i r f a t t y a c i d re s e r v e s w h e n n o t f e d( D y e , 1 9 8 0 ; A b l e t t a n d R i c h a r d s , 1 9 8 0) .

    S e c o n d , t h e a l g a e s e rv e t h e f u n c t i o n o f p i c k i n g u p i n o r g a n i c w a s t ep r o d u c t s i n t h e r e a ri n g ta n k s , t h e r e b y r e p r o d u c i n g a n d u l t i m a t e l yf o r m i n g t h e b a s i s o f s o m e r e p r o d u c t i o n o f B r a c h i o n u s d i r e c t l y i n t h et a n k s. F o r t h e f ir s t t w o w e e k s , d u r i n g w h i c h t h e r e a r in g s y s t e m w a s n o tc o n n e c t e d t o t h e w a t e r t r e a t m e n t u n i t , alg al a c t iv i t y e f f e c t i v e l y k e p tt h e a m m o n i a c o n c e n t r a t i o n b e l o w 0 .1 m g N H ~ - N l i t re -1. I n t h e a b s e n c eo f a l g a e t h e c o n c e n t r a t i o n w o u l d r e a c h cr it ic a l v a lu e s o f m o r e t h a n7 m g N H ~ - N l i t r e -x . T h i s o b s e r v a t i o n is i n c o n t r a s t t o e a r l i e r f i n d in g st h a t m e a s u r a b l e r e d u c t i o n s in a m m o n i a l ev els w e r e o b t a i n e d o n l y a tl ig h t le ve ls o f a b o u t 4 0 0 0 1 u x ( A l d e r s o n a n d H o w e l l , 1 9 7 3 ). T h er e a s o n f o r t h is d i s c r e p a n c y is n o t q u i t e c l e a r, b u t i t m i g h t be d u et o q u a l i t a ti v e d i f f e r e n c e s b e t w e e n t h e l ig h t so u r c e s .

    T h e l ig h t a p p l ie d a t t h e s u r f a c e , a p a r t f r o m i l l u m i n a t i n g t h e f o o di t e m s t o t h e g r a z i n g f is h l a rv a e a n d s u p p l y i n g l ig h t e n e r g y t o t h e a lg a e ,s e rv e s as a n a t t r a c t a n t t o t h e p o s i t i v el y p h o t o t a c t i c A r t e m i a n a u p l i i a n dB r a c h i o n u s . H e n c e , t h e f o o d a n i m a l s t e n d t o c o l l e c t i n t h e u p p e r p a r to f t h e w a t e r c o l u m n w h e r e t h e f i sh la r va e a ls o c o n c e n t r a t e d u e t o t h eu p w e l li n g w a t e r ( w h i c h k e e ps t h e m s e p a ra t e d f r o m t h e b o t t o m l a y e rw h e r e w a s t e p a r t i c le s a n d d e a d l a rv a e a r e c o l l e c t e d a t t h e c o n u s a v ds i p ho n e d o r t a p p e d t h r o u g h t h e b o t t o m o u t l e t ) .

    T h e w a t e r c i r c u l a ti o n p a t t e r n i n t h e s y s t e m , c o m b i n e d w i t h t h e li g hte f f e c t s , t h e r e f o r e , r e su l t s i n m a x i m i z a t i o n o f t h e c o n t a c t s u rf a c eb e t w e e n t h e f is h l ar v a e a n d t h e i r f o o d i t e m s w i t h o u t i n f l ic t in g a n ym e c h a n i c a l st r es s o n t h e l a r va e .

    A n o t h e r i m p o r t a n t f a c t o r i n t h e s u c c e s s o f a s y s t e m s u c h a s t h is is t ok e e p t h e w a t e r a t a c o n s t a n t a n d g o o d q u a l i t y , e sp e c i a ll y w i t h r e s p e c t

    i t o s a l in i t y . I t h a s b e e n s h o w n t h a t a h i g h s a l i n it y , o f 3 3 - 3 4 % 0 , c a n g iv eb u o y a n c y t o a g r e a te r n u m b e r o f fi sh la rv ae ; t hi s r e d u c e s t h e n u m b e r

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    8 J . O . Olesen , F. M inck

    which would otherwise sink to the bottom and die from starvation. Asit is commonly observed that the ability of fish larvae to float variesfrom batch to batch, keeping a constant and high salinity can give thenon-floating larvae the opportunity of active feeding with minimalexpenditure of 'swimming energy'.

    The significance to turbot rearing of this technique is uncertain aswork done on the Black Sea turbot suggests that larval floating capacityis directly associated with some biological quality expressed as differentwater contents in the larvae (Vorob'eva and Zhukova, 1978). On theother hand, it is believed by these authors that the disturbance of egghydration during maturation may be caused by both inadequate main-tenance conditions and artificially induced biological changes in thebroodstock. The present investigation certainly has shown that weaklarvae o f oceanic origin survive be tte r in high-salinity water (34~/oo S)than in low-salinity water (230/00 S).

    The growth of larvae shown in Table 2 can be taken as an indicationof the good development of the larvae during the rearing period, as thepresented growth corresponds well to results reported by other scien-tists (Person-Le Ruyet e t a l . , 1978; Quantz e t a l . , 1980; Hansen andChristensen, 1980). Irrespective of minor differences in experimentalconditions the larvae reached the same weight after 35 days of growth(Fig. 2). It seems that the actual growth rate of larvae during the first10 days is somewhat superior compared to the other exper iments; afterthis it levels off to the same rate. If this is seen to be consistent, itmight be an effect of the technical set-up tending to maximize contactbetween the poorly swimming young larvae and their prey.

    A more interesting feature of the system is the capacity for pro-ducing a certain number of larvae which, apart from some incidentswith losses due to external technical failures, seems to be quite constantirrespective of the initial stocking of the rearing tanks above a min imumdensity (Table 1). The figures presented in Table 1 indicate that eachrearing tank has the capacity for production of 800 40-day-old larvae,corresponding to 6.4 larvae litre -1 or 3000 larvae metre-2 of surfacearea, using a stocking density of 2000 larvae tank -~ or 16 larvae litre-I ;this corresponds to a survival rate of 40%. Raising the stocking densityleads to a reduction in survival rate and constant larvae production.Further experiments seem to indicate that any reduction in stockingrate below 2000 larvae tank -~ is followed by a reduc tion in the numb erof larvae produced.

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    A technica l solu tion to the mass-culturing o f larval turbot 9

    t 0 0

    10 . ~

    1 .0

    0 . 1

    0 . 0 1

    D R Y W E I G H T , r n g

    K 1

    12

    13

    2

    vA

    2 ' i

    21

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    21 3

    1 0 2 0 3 0 4 0 D A Y S

    F i g . 2 . G r o w t h o f t u r b o t l a rv a e d u r i n g t h e f ir s t m o n t h o f d e v e l o p m e n t . ( 1 , Q u a n t zet al. ( 1 9 8 0 ) : g r o w t h a t a m e a n t e m p e r a t u r e o f 1 5 . 1 C - p a r t o f t h e d a t a i s c a lc u -l a t ed o n t he ba s i s o f we igh t / l eng th r e l a t i onsh ip a f t e r Jone s (1972 ) . 2 , Pe r son -LeR u y e t et al. ( 197 8 ) : f i gu re s ca l cu l a t ed on t he ba s is o f g row th in fr e sh we igh t a t1 9 C w i t h a d r y w e i g h t t o f r e sh w e ig h t ra t i o o f 0 . 2 0 . 3 , H a n s e n a n d C h r i st e n se n( 1 9 8 0 ) : g r o w t h a t 1 5 C - f ig u r e s a r e m e a n w e i g h ts o f d i ff e r e n t s iz e -g r o u p s a t ac e r t a in a g e. , O w n d a t a : c a l c u l a t e d o n b a s is o f t h e m e a s u r e d f r e s h w e i g h ts f r o mTab le 2 w i th a meas u red d ry t o f r e sh we igh t r a t i o o f 0 .20 . A , Mean -+ s t anda rd

    d e v i a t i o n . )

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    10 J . O . O l e s e n , F . M i n c kO / o ' i100

    80

    60

    40

    20

    o

    S u r v i v a l~X X ~x

    ~ " ' ~ x x ~ x.. ~ . - , . , X w

    . . . . . . . . . . . . , , , ; o , , , , ,6 1 0 1 4 1 8 2 2 34 38D a y s a f t e r h a t c h i n gFig. 3. Survivalof turbot larvae from Day 2 to Day 38.

    Figure 3 presents the conclusion of the experimental indications inthe form of a percentage survival curve, which seems to be valid for therearing tanks with stocking densities of about 2000 larvae tank -1. Com-parisons to survival rates reported by other researchers generally showthese to be somewhat lower under similar conditions of stocking andfeeding. Kingwell e t a l . (1977) obtained an average survival of 15%from Day 2 to Day 20, and Person-Le Ruyet e t a l . (1978) reported anaverage survival of 32% from Day 1 to Day 40 but with much variationbetween batches; Howell (1979) reported average survival rates atDay 14 of 35 and 47% for white and black tanks, respectively, using astocking density of approximately 5 larvae litre -1. The survival rate atDay 14 in the present experiment was about 60% with no differencebetween light coloured (red) and black tanks. Quantz e t a l . (1980)reported survival rates as high as 50% from Day 3 to Day 36 and 34%from Day 3 to Day 26 in two year groups using a diet of mixed zoo-plankton. However, in the experiments of Quantz e t a l . the stockingdensity was very low, being about 0.25 larvae litre-~ compared to16 larvae litre-1 in the present experiment.

    CONCLUSIONThe results of these experiments indicate that the system tested can beused for the mass-rearing of turbot larvae eliminating, at the same time,minor d ifferences in egg qualities. This is evident f rom the relatively

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    A technical so lu t ion to the mass-cul tur ing o f larval turb ot 11c o n s t a n t p r o d u c t i o n c a p a c i t y o f s in g le t a n k s c o m p a r e d t o t h e r e s u lt s o fo t h e r e x p e r i m e n t s ( K i n g w e l l e t a l . , 1 9 7 7 ; P e r s on - L e R u y e t e t a l . , 1 9 7 8 ) .T h e r e l e v a n c e o f t h i s c a n b e s e e n b e s t in a s i t u a t i o n w i t h l i m i t e d eg gs u p p l i e s .

    R E F E R E N C E SAb le t t , R . F . & R icha rds , R . H . (1980) . Su i t ab i l it y o f twe n ty - fo u r hou r and fo r ty -

    e igh t -hour un fed A r t e m i a as an ea r ly foo ds tu f f fo r ' 0 ' g roup Dove r so le (Soleasolea L . ) p r o d u c t i o n . A q u a c u l t u r e , 1 9 , 3 7 1 - 7 .

    A lde rson , R . & Howe l l , B. R . (1973) . The e f fec t o f a lgae on the wa te r cond i t ions inf ish rear ing tanks in re la t ion to the gro wth o f juveni le so le (Solea solea L.).A q u a c u l t u r e , 2 (3 ) , 281-8 .

    Brom ley , P . J . (1978) . The w ean ing o f ha tch e ry rea red tu rb o t l arvae ( S c o p h t h a l m u sm a x i m u s L.) on a dry d ie t . A q u a c u l t u r e , 1 3 , 3 3 9 - 4 5 .

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    Dye , J . E . (1980 . The p rod uc t ion and e f f i c ien t u se o f f r e sh ly ha tche d b r ine sh r impnaupl i i ( A r t e m i a ) in the larval rear ing of marine f i sh a t the ha tcher ies o f theBrit ish W hi te Fish Au tho r i ty . In : The Br i ne Shr i m p A r t e m i a - 3. Ecology ,Cu l t u r i ng and U se i n Aquacu l t u re , eds. G. Persoone, P. Sorgeloos, O. Roels andE. Jaspers, Universa Press, Wetteren, 456 pp.

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