Poxton 1982 Aquacultural-Engineering 1

7/28/2019 Poxton 1982 Aquacultural-Engineering 1

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Aqu acul tura l Engineering 1 (1982) 23-34

T H E G R O W T H O F T U R B O T ( S C O P H T H A L M U S M A X I M U S ( L . ) )I N R E C I R C U L A T I N G S Y S T E M S

M. G. POXTON,'~ K. R. MURRAY:~ and B. T. LINFOOT~t Dep a r t men t o f Br ew i n g a n d B i o lo g i ca l S c i en ces a n d J; Aq u a cu l t u r a l En g i n eer i ng Gr o up ,He r io t .W at t Universi ty , C ham bers S t , Edinburgh E H1 1HX , UK

A B S T R A C TO-group wi ld turbot ( S c o p h t h a l m u s m a x i m u s ( L . ) ) w e r e u s e d i n a n u m b e r o f f e e d i n gexp erim en ts desig ned to assess the use fulness o f readily avai lable species o f indu strialf i sh a s f e e d f o r t he ongrow i ng stage o f cu l t i va ti on ( 1 0 - 5 00 g ). Spra t s ( S p r a t t u s s p r a t t u s(L . } ) a nd sandeel s ( A m m o d y t e s m a r i n u s Ra i t t ) were t he m os t succes s fu l i n tha t f e ed -ing ra tes o f 2% l ive w eigh t per f ee d gave co nvers ion e f f ic ienc ies wh ich were general lybe t ter than 3 : 1. A regular regime o f tw o feed s a day sh ouM give gro wth ra tesapproach i ng 2% per day r e su l t i ng i n an ongrowi ng per i od o f abou t 200 days a t 16 C.The turb ot were m ainta ined in c losed ree i rcula t ing sys tems us ing a simple des ign fo rt he t r ea t m en t un i ts . These p rov i ded a s tab l e env i ronm en t i n wh i ch t o co ndu c t t heexpe r ime nts the average wa ter qua l i t y con di t ions be ing g iven. There were f e w heal thprob l em s a nd t he t a st e and t ex t ure o f t he f i sh p rodu ced appeared t o be good .

INTRODUCTIONThe use o f re c i r cu la t i ng wa t e r sy s t em s i n aquacu l t u r e ha s r ecen t l y b een r ecogn i zeda s b e i n g o f m a j o r i m p o r t a n c e . T h e y r a n g e f r o m s i m p l e re -u s e o f so m e o f t h e c u l t u r ew a t e r t o m o r e c o m p l e x c l o s e d s y s t e m s e m p l o y i n g t o t a l r e c i r c u l a t i o n o f a l l t h e w a t e r .T h e r e i s a n e x t en s i v e l i te r a t u re o n t h e t e c h n i q u e s e m p l o y e d m u c h o f w h i c h h a s b e e nr e v ie w e d b y K i n n e ( 1 9 7 6 ) a n d M a y o ( 1 9 7 9 ) . I n M a y 1 9 8 0 a t e c h n ic a l s y m p o s i u m o nn e w d e v e l o p m e n t s i n t h e u t i li z a t io n o f h e a t e d e f f l u e n t s an d o f r e c i rc u l a ti o n s y s t e m sfo r i n t ens ive aquacu l t u r e was ho ld i n S t avange r . These new pape r s t oge the r w i th

23Aq u a cu l t u r a l En g i n eeri n g 0 1 4 4 -8 6 0 9 1 8 2 / 0 0 0 1 -0 0 2 3 / $ 0 2 . 7 5 Applied Science Publishers Ltd,England, 1982Printed in Great Britain


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24 M.G. POXTO N, K. R. MUR RAY, B. T. LINEOO Ti m p o r t a n t c o n c l u s io n s a n d r e c o m m e n d a t i o n s h a v e b e e n p u b l is h e d ( T ie w s , 1 9 81 ) a n di t is o f i n t e r e s t t o no t e t ha t i t was f e l t t ha t t he t e c hno logy o f t he sy s t ems was we l lahead o f t he i r app l i ca t i ons . The app l i ca t i ons a r e many and d ive r se bu t complex , c lo sedr e c ir c u la t in g s y s t e m s c a n b e c o n s i d e re d f o r b r o o d s t o c k , h a t c h e r i es a n d o n g r o w i n g .

T h e p r e s e n t p a p e r i s c o n c e r n e d w i t h t h e o n g r o w i n g o f t h e t u r b o t (Scophthalmusmaximus (L . ) ) i n c lo sed r ec i r cu l a ti ng sys t ems . The de s ign and pe r fo rm anc e o f t hes y s t e m s t h e m s e l v es h a v e b e e n r e p o r t e d a t t h e S t a v a n g e r s y m p o s i u m ( P o x t o n et aL,1980) . T he t u rbo t i s a va luab l e mar ine f l a t fi sh wh ich ha s been i den t i f i ed a s hav ingc o n s i d e ra b l e p o t e n t i a l f o r f a r m i n g ( Jo n e s , 1 9 7 2 ; P u r d o m et aL, 1972 ; Ke r r , 1976 ) bu ta s ye t t he r e a r e no commerc i a l l y ava i l ab l e d i e t s . Howeve r , a s a r e su l t o f cons ide rab l ee x p e r i m e n t a t i o n t h e B r i t i s h W h i t e F i s h A u t h o r i t y ( W F A ) h a s d e v e l o p e d a r a n g e o fm o i s t pe l l e ts (Tha in and U rch , 1972 , 1973 ) . The cos t o f p roduc ing t he se pe l l e t s i sc o n s i d e ra b l e t h o u g h a n d i n c o m p a r a t i v e t r ia l s b e t w e e n t w o s u c h f o r m u l a t i o n s , W F A 6a n d W F A 7 , a n d w h o l e s p r a ts , Sprattus sprattus (L . ) , t he l a t t e r we re shown tog ive equa l l y good , i f no t be t t e r , f o od conve r s ions (Hu l l and Edw ards , 1979 ) . S incesp ra t s a r e cheape r t he i r u se a s a f e ed may cons ide rab ly r educe ong rowing cos t s . Thesee x p e r i m e n t s w e r e d e s i g n e d t o c o m p a r e t h e g r o w t h , s u r v i v a l a n d c o n v e r s i o n r a t e o ftu r bo t f ed on t he l a t e s t ava i l ab le mo i s t pe l l e t (W FA 7 ) w i th t ha t o f sma l l and l argespra ts , sandee ls (Ammodytes marinus R a i t t ) a n d w h i t i n g (Merlangius merlangus (L . ) ) .P o p u l a t i o n s o f t u r b o t o f d i f fe r e n t s iz e w e r e o b t a i n e d i n o r d e r t o id e n t i f y t h e a p p r o p r i -a t e s t age o f ong rowin g a t wh ich t he va r ious foods cou ld be i n t roduced . S ince al l t hee x p e r i m e n t s w e r e c a r r i ed o u t w i t h c o m m e r c i a l a p p l i c a t i o n in m i n d t h e t a s te o f t h et u r b o t p r o d u c e d i n c lo s e d s y s t e m s w a s a ls o c o n s id e r e d i m p o r t a n t .

MATERIALS AND METHODSSource of materialsTurbot. Wild caug h t t u rbo t f r om Bor th , Mid-Wale s, we re supp l i ed by WFA f romt h e i r t a n k s a t H u n t e r s t o n . F u r t h e r w i l d t u r b o t w e r e c a u g h t l o c a ll y a t D u n b a r . I n b o t hcase s t he se we re t r anspo r t ed t o Ed inbu rgh i n 100 l i t r e PVC dus tb in s .

Diets. The m o i s t pe l l e t s u sed we re W FA 7 spec i f i c a t ion (Hu l l and Edwards , 1979 ) .Sp ra t s an d sm a l l wh i t i ng we re pu rchased l oca l l y f rom a F i r t h o f Fo r th ca t ch . Sandee l sw e r e o b t a i n e d f r o m G r i m s b y F i s h M e r c h a n t s , ex N o r t h S e a ca t c h es .Diet storage and preparation

All d ie t s were ke pt in a deep f reez e . Pr ior to feeding , the indus t r ia l f i sh , spra ts ,s andee ls and wh i t i ng , we re cho ppe d i n to e longa t ed s t r ip s o f d i f fe r en t l eng ths andb read ths . Th i s was l a rge ly dep end en t on t he s iz e r ange o f t u rb o t t hey w e re to bef ed t o . These p iece s we re t hen a l l owed to t haw ou t and p r io r t o f eed ing we ighed . I nthe ca se o f t he w h i t ing , b e fo re f r eez ing t he heads and v i s ce ra we re d i s ca rded .


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GROWTH OF TURBOT IN RECIRCULATING SYSTEMS 25Feeding pro cedure

T h e f i s h we r e f e d tw ic e a d a y ; fi v e ( 5 ) d a y s p e r we e k a t a r a t e n o t e x c e e d in g 5 % li vew e i g h t p e r d a y ( w e t / w e t b a si s) . A l l f e e d i n g w a s b y h a n d a n d a n y s u r p lu s , u n e a t e n f o o dwa s d i s c a r d e d . I n t h e c a s e o f t h e p r e p a r e d i n d u s t r i a l f i s h , a ll th e p i e c e s we r e wa s h e dt o r e m o v e s u r f a c e m a t e r i a l a s w i t h o u t t h i s a l a rg e q u a n t i t y o f d e b r i s w a s l e f t f l o a t i n g i nth e f i s h t a n k s .Grading

B e f o r e a n y e x p e r i m e n t s t h e f is h w e r e g r a d e d i n t o w e i g h t ca t e g o r ie s a n d as t h ew h o l e p r o g r a m m e c o n t i n u e d t h e r e w a s a p r o g re s s iv e s h if t u p t h e w e i g h t s p e c t r u m a sth e f i s h g r e w .

First experiment ( D a y 1 - 1 4 )T h e f i s h we r e g r a d e d i n to f i v e c a t e g o r i e s o v e r t h e s i z e r a n g e i n d i c a t e d i n t h e t a b l e .E a c h c a t e g o r y w a s t h e n s p li t i n t o e q u a l n u m b e r s s o th a t a c o m p a r i s o n c o u l d be m a d eb e t w e e n f e e d i n g o n e g r o u p ( G r o u p A ) w i t h m o i s t p el l et s ( W F A 7 ) a n d t h e o t h e r ,G r o u p B w i t h s p ra t s.Second experiment ( D a y 1 4 - 2 8 )

I n t h i s t im e - p e r io d G r o u p A f i s h we r e f e d s m a ll s p r a t s a n d G r o u p B l a rg e s p r a t s( s e e t a b l e ) . A t t h e e n d o f t h i s e x p e r im e n t i t wa s e ss e n t i al t o r e g r a d e al l t h e f i s h b e f o r es e t t i n g u p t h e n e x t e x p e r i m e n t .Third experiment ( D a y 2 8 - 7 0 )

T w o n e w c a t e g o r i e s (s e e T a b le 4 ) w e r e s p li t i n t o t h e t w o g r o u p s A a n d B s o t h a t ac o m p a r i s o n c o u ld b e m a d e b e tw e e n a l a r g e s p r a t s d i e t a n d a s a n d e e l d i e t. S in c e t h e r e i sn o p u b l i s h e d i n f o r m a t i o n o n t h e u s e o f sa n d e e ls o r w h i t i n g t h i s, an d th e f o l lo w i n ge x p e r i m e n t , w e r e c o n d u c t e d o v e r a l o n g e r ti m e - p e r i o d .Fourth experiment ( D a y 7 0 - 1 3 3 )

W i t h t h e e x t e n d e d t im e - s c al e o f t h is a n d t h e p r e v i o u s e x p e r i m e n t r e -g r a d in g i n t on e w c a t e g o r i e s w a s n e c e s s a r y ( s e e T a b l e 5 ) , b e f o r e p r e s e n ti n g t h e t w o g r o u p s t o e i t h e ra s a n d e e l o r wh i t i n g d i e t .Recirculating systems and water quality

T h e d e s ig n o f t h e r e c i r cu l a t in g s y s t e m s ha s b e e n d e s c r i b e d ( P o x t o n et a / . , ( 1 9 8 1 ) ,b u t i s s h o wn a g a in h e r e f o r c o n v e n i e n c e i n F ig . 1. P o ly p r o p y l e n e f i sh t a n k s ( a re a0 .3 7 m 2 ) we r e f i ll e d t o a b o u t 2 0 c m wi th 7 5 l i t re s o f wa t e r . T h e f i l t e r b e d s ( 0 .9 m s )w e r e f il le d t o a d e p t h o f 3 0 c m w i t h a b o u t 4 0 0 k g o f c o a r s e ( 6 m m ) g r a n it e g ra v elc h ip s , g iv in g a p o t e n t i a l s u r f a c e a r e a f o r b a c t e r i a o f a b o u t 1 8 0 m E. A l l t h e wa t e r w a sr e c y c le d t h r o u g h P V C p i p e b u t lo s se s a m o u n t e d t o a b o u t 1% p e r d a y fr o m e v a p o r a-t i o n , c l e a n in g a n d s a m p l in g . S a l i n i t y wa s m a in t a in e d a t 3 4 + 2 % b y t h e r e g u l a r a d d i -


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26 M.G. POXTON, K . R. MURRAY , B. T . LINFOOT

h e a d t a n kf i s h t a n k s

. I J__K E Y ;

a - d e n ~ t r ~ yi n g a lg a e s y s t e mm - m e c h a n i c a l f i l t e rw - b a c k w a s h ,"

a i r f l i t s~r/Fig, 1 . Recirculatory cu l ture uni t .

t i o n o f a e r a t e d t a p w a t e r , w h i l s t o t h e r l o s s es w e r e m a d e g o o d b y n e w s e a w a t e r .T e m p e r a t u r e c o n t r o l w a s a c h i e v e d b y r e g u l a ti n g t h e a m b i e n t a i r t e m p e r a t u r e t o1 6 + 2 C . F l o w r a t e s w e r e r e g u l a t e d t o g i ve a t o t a l s y s t e m t u r n o v e r t i m e o f a b o u t 2 h .

P o r t a b l e m e t e r s w e r e u s e d to m o n i t o r t h e s a l in i ty , p H a n d d i s s o l v e d o x y g e n c o n c e n -t r a t i o n ( D . O . ) . T h e w a t e r w a s re g u l a r ly a n a l y s e d fo r a m m o n i u m a n d n i t r it e n i t ro g e nu s in g t h e m e t h o d s o f S o l o r z a n o ( 1 9 6 9 ) a n d B e n d s c h n e i d er a n d R o b i n s o n ( 19 5 2 ) .F o r n i t r a t e a n a l y s i s 'H a c h r e a g e n t p i l l o w s ' ( H a c h C h e m i c a l C o . , A m e s , I o w a 5 0 0 1 0 ,U S A ) w e r e u s e d , t h e r e s u l t i n g a m b e r c o l o u r a t i o n b e i n g m e a s u r e d a t a p e a k a b s o r b a n c eo f 5 4 5 n m . T h e c o n c e n t r a t i o n s o f u n i o n i z e d a m m o n i a , n i tr i te a n d n i t r a t e i o n s w e r et h e n c a l c u l a t e d .

R E S U L T S

T h e w a t e r c o n t e n t o f t h e v a ri o u s fe e d s w a s d e t e r m i n e d ( T a b l e 1) i n o r d e r t o b e a b l e toc o m p a r e f e e d c o n v e r s i o n e f f i c i e n c i e s o n a d r y a s w e l l as a w e t w e i g h t b a s is . T h r o u g h -o u t t h i s p a p e r f e e d c o n v e r s i o n r e f e r s t o w t . o f f e e d e a t e n ( g ) / w t . o f f i s h p r o d u c t s ( g ).


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G R O W T H O F T U R B O T I N R E C I R C U L A T I N G S Y ST E M S 2 7

T A B L E 1T h e w a t e r c o n t e n t o f t h e v a ri o u s f o o d s u s e d a n d o f t h e t u r b o tp rodu c e d du r i ng t he f e e d i ng t r ia l sFo od % W ate r % Dry

Moi s t pe l l e t (W F A 7 ) 40 60Sm all sprat (2.5 g) 79 21Large spra t (12 .4 g) 73 27Sandee ls 81 19Whi t inga 79 21T u r b o t p r o d u c e d 7 9 2 1a Refe rs to usable pa r t o f whi t ing (50%).

T h e m a i n d i f f e r e n c e in t h e se e x p e r i m e n t s w a s b e t w e e n t h e m o i s t p e l le t s ( 4 0 %w a t e r / 3 6 % p r o t e i n ) a n d t h e i n d u s t ri a l f is h s p e ci es ( 7 3 - 8 1 % w a t e r / 1 5 % p r o t e i n ) . N od a t a o n p r o t e i n u t i l i z a t i o n w i l l b e p r e s e n t e d h e r e , t h e p r o t e i n l e v e l s o f th e f e e d s a rea p p r o x i m a t e v a l u e s g iv e n f o r i n f o r m a t i o n o n l y . A f u l l e r a n a ly s i s o f th e p e l l e t s isa v ai la b le in H u l l a nd E d w a r d s ( 1 9 7 9 ) , w h i l s t f o r th e g r o ss c o m p o s i t i o n o f c o m m e r c i -a l ly i m p o r t a n t s p e c ie s o f U K f i s h r e f e r e n c e s h o u l d b e m a d e t o M u r r a y a n d B u r t (1 9 6 9 ) .

T h e r e s u l ts o f t h e i n d i v i d u a l f e e d i n g e x p e r i m e n t s a r e p r e s e n t e d i n T a b l e s 2 - 5 a n da re s u m m a r i z e d i n T a b l e 6 . T h e r e w a s a s l ig h t t e n d e n c y f o r t h e f e e d i n g r a t e o f t h e f is h

T A B L E 2Resul t s of the feeding t r ia l, semi-mois t pe l le t (WFA 7) / smal l spra t. 19 Ap ri l -2 May (Days 1-14 )No m inal s ize Mean we ight o f Weight o f Total b iomass Convers ioncategory f ish (gj fo od Jed (g) e f f ic iencies(e) (g)In i t ia l Final ln i t ia l Final Wet wt . Dry wt .

Group A . Se mi -mo i s t pe l l e t d i e t (W FA 7 )< 5 3-4 4-4 12.4 31.0 39.7 1.4 4.15-1 0 7 .6 8-7 71 .6 220.6 252.2 2-3 6-510- 20 14-6 17.3 273.9 992 .2 1 173.7 1.5 4.320 -30 23.3 26 .2 320.3 1 001.6 1 127.1 2 .6 7 .330--40* 32.9 35-0 280.7 1 021.2 1 085.1 4-4 12.6

M ean/T ota l s 18 .1 20-4 958.9 3 266.6 3 677-8 2 .3 6 .7*Exp t s . e xc l ude d 2 .0 5 -6Group B. Smal l sprat d ie t5-1 0 7 .6 9 .0 94 .4 220-7 261.0 2-3 2 .310- 20 14.6 16.6 432-8 991 .6 1 128.8 3-2 3-220- 30 23.3 26 .4 417-0 10 02 .0 1 135.6 3-1 3-130-4 0 33-0 38 .5 446.9 1 022-4 1 193.2 2 .6 2 .6> 4 0 5 5 .8 6 6 . 4 4 4 6 .1 1 0 5 9 . 6 1 2 6 1 . 0 2 .2 2 .2

M ean/T ota l s 22 .6 26 .2 1 837.2 4 296-3 4 979.6 2-7 2 .7


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28 M. G. POXTON, K. R. MURRAY, B. T. LINFOOT

TABLE 3Results of the feeding trial, small sprat/large sprat. 2-16 May (Days 14-2 8)

No min al s ize Mean we igh t o f Weight o f Total b iomass Conversioncategory f ish (g) fo od fe d [g) e f f ic iencies( g ) ( g ~In i t ia l Final In i t ia l Final Wet wt . Dr) ' wt .Group A . Sma l l sp ra t d i e t< 5 4.4 5.8 31.2 39-7 52.5 2.4 2.45-10 8.7 11.3 167.2 252.2 328.2 2.2 2.210-20 17-3 21-9 733.9 1 173.7 14 91 .3 2.3 2.320-30 26.2 31.8 623.9 1 127.1 1 368.5 2-6 2.630-40 35-0 49.2 715.6 108 5.1 147 4.9 1-7 1-7

Mean/Totals 20-4 24.0 2 271-8 3 266.6 4 715-4 2.2 2-2Group B. Large sprat d ie t5-1 0 7.6 11.6 176-0 261.0 335.2 2.4 3.010-2 0 14.6 22.6 751.4 1 128.8 1 538.8 1.8 2.420- 30 23.3 34-5 698-3 1 135.6 1 484-8 2.0 2.630-40 33.0 45-4 542.7 1 193.2 1 406.9 2.5 3.3> 4 0 55-8 86.0 801.8 126 1-0 1633- 1 2.2 2.8

Mean/Totals 22.6 40.0 2 970.2 4 979. 6 6 398.8 2-2 2.8

TABLE 4Results of the feeding trial, large sprat/sandeels. 16 May-27 June (Days 28-70)No m ina l s ize Mean we igh t o f Weight o f Total b iomass Conversioncategory f i sh (g) foo d fed /g) e f f i c ienc ies( g ) ( g )In i t ia l Final In i t ia l Final Wet wt . Dr) , wt .

Group A. Large sprat d ie t< 10 7.7 13-3 447 .8 231. 2 398-1 2-7 3.410-15 12.6 24-9 673.5 327.1 648.1 2.1 2.715-25 20.3 35-1 1 354.9 793.0 1 369.2 2.4 3.025-35 28.6 54.6 245 3.9 125 8.6 2401-1 2.2 2.835-45 39.7 75.3 2 004.2 1 070.8 2 032.5 2.1 2.745- 60 50.8 96-3 1 752-7 915.2 1 734.0 2.1 2.8Mean/Tota ls 26-6 49-9 8 687.0 4 595.9 8 583.0 2-3 2-9

Group B. Sandee l d ie t10-15 13.6 25.5 806.2 381.7 713.4 2.4 2-315-25 20-7 40-5 1 761-2 786.1 1 537.3 2-4 2.225-35 a 30-1 41-7 1 483-2 1 326-0 1 833-9 2.9 2.735-45 40.2 72-0 2 038-5 1 085.0 1 944-7 2.4 2.245-60 52.1 91-6 1 621-7 885-2 1 557-9 2.4 2.260-80 71.2 129.7 1 484.5 783-7 1 427. 0 2-3 2-1> 80 104.4 197.4 2 441.8 939-6 1 770.0 2.9 2.7Mean/Totals 47-5 85-8 11 637.1 6 187-3 10 791.1 2-5 2-3

a This particular trial was ended on 13 June (Day 56).


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GROWTH OF TURBOT IN RECIRCULATING SYSTEMS 29

TABLE 5Results of the feeding trial, sandeels/whiting. 27 June-29 August (Days 70-133)No m ina l s ize Mean we ig ht o f Weight o f Total b iomass Convers ioncategory f ish (g) fo od fe d (g) e f f ic iencies(g) (g)In i t ia l Final In i t ia l Final Wet wt . Dry wt .

Group A . Sa nde e l d i e t< 20 14-2 31.7 1 790.9 523.7 1 172.3 2.8 2.520-30 24.4 48-9 1 656.7 561.8 1 125.6 2.9 2.730--40* 35-2 39.3 1 265.2 843.8 942-7 12.8 11.640-55* 48.6 62.6 2 028.2 1 362.0 1 753.4 5.2 4.755-70 59.8 117-8 3 448.0 1 255.1 2 474.8 2-8 2.670-85 77.0 164-3 4 005.2 1 308.6 2 792.8 2.7 2.4Mean/Totals 43-2 77.4 14 194.2 5 855.0 10 261-6 4-9 4.4*Expts. excluded 2.8 2.6

Group B. Whi t ing d ie t20-30* 23.9 31.5 1 025.0 549.8 723.8 5.9 5.930--40 35.3 80.8 2 765.2 847.9 1 938.3 2.5 2.540-55 45.2 103.1 4 112.4 1 266.8 2 886.7 2.5 2.555-70 63.8 106.2 2 555.4 1 276.1 2 124.7 3.0 3.070-85 77.3 151.6 3512 '0 1 313.3 2577. 4 2.8 2.885-100 89.3 205.5 5 167.2 1874.4 4315 .0 2.1 2-1100-120 104-9 169.6 3 717.4 2 098.6 3 392-9 2.9 2.9> 120 172.0 374.1 7 969.0 2 924-4 6 360.0 2.3 2.3Mean/Totals 76.5 152.8 30 823-6 12 151-3 24 318.8 3-0 3-0* Expts. included 2.6 2-6

TABLE 6Summary o f the feeding trial results. 19 April-29 August 1977D ie t Leng th o f No. days Feeding rate as % o f Mean conversiontrial fe d l ive f ish wt. e f f ic iencies(days) (feed- ~) (day -~) We t wt . D ry wt.

Moist pelle t 1-14 8 1.8 2.0 2.0 5-6Small sprat 1-14 8 2.5 2.8 2.7 2-7Small sprat 14-28 12 2-4 4.1 2-2 2. 2Large sprat 14-28 12 2-2 3.7 2-2 2.8Large sprat 28-70 31 2-2 3-1 2.3 2-9S a n d e e l 28-70 31 2.2 3-3 2.5 2.3S a n d e e l 7 0 - 1 3 3 4 2 2 . 1 2 - 8 2 - 8 2 - 6Whiting 70-133 42 2-0 2-7 2.6 2-6


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30 M.G. POXTON, K. R. MURRAY , B. T. LINFOO T

t o d e c r e a s e a s t h e y g r e w in s iz e b u t f e e d in g r a t e s we r e g e n e r a l l y i n e x c e s s o f 2 % li vew e i g h t p e r f e e d . T h e r e d u c t i o n i n f e e d i n g r a te w a s m o s t n o t i c e a b l e a m o n g s t t h o s ef i sh b e in g f e d o n t h e m o i s t p e l l e t d i e t ( W F A 7 ) wh e r e f e e d in g r a t e s d e c l i n e d t o 1 .6%liv e w e i g h t p e r f e e d . I n a d d i t i o n , c o n v e r s i o n e f f ic i e n c y o f t h e t u r b o t f e d o n W F A 7d e c l i n e d w i th i n c r e a s in g s i ze o f t h e fi s h ( T a b l e 2 ) . No s u c h t r e n d w a s e v id e n t w i th a n yo f t h e i n d u s t r i a l f i s h d i e t s . Ho we v e r , i t m u s t b e p o in t e d o u t t h a t i t i s e s s e n t i a l t op r e s e n t f e e d o f a n a p p r o p r i a t e s iz e a n d s h a p e f o r t h e f u ll r a t i o n t o b e c o n s u m e d . T h ef a c t t h a t a f u ll s i ze r a n g e o f t h e m o i s t p e l le t s wa s n o t a v ai l ab l e c o u ld h a v e p r o d u c e d ab i as i n b o t h o b s e r v a t i o n s . T h e m e a n c o n v e r s i o n e f f i c i e n c y f o r t u r b o t o f 5 g ~ 2 0 - 3 0 go b t a i n e d o n a w e t w e i g h t b a s is w a s t h e s a m e a s t h a t o b t a i n e d b y t h e W F A t h e m s e l v e s( 2 .0 : 1 ) ( Hu l l a n d E d wa r d s , 1 9 7 9 ) . T h e i n d iv id u a l e ff i c i e n c i e s o b t a in e d f o r t u r b o t i nt h o s e s iz e c a t eg o r i e s w a s g e n e r a l ly b e t t e r t h a n t h a t o b t a i n e d b y f e e d i n g s pr a t s ( T a b l e s2 a n d 3 ) o n a w e t b u t n o t o n a d r y w e i g h t b a si s. G o o d c o n v e r s i o n e f f ic i e n c ie s w e r eo b t a in e d w i th a ll t h e d i e t s b e in g g e n e r a l l y b e t t e r t h a n 3 : 1 o n b o th a we t a n d d r ywe ig h t b a s is . As a r e s u l t h ig h g r o w th r a t e s we r e o b t a in e d i n t h e r a n g e 1 - 2 -5 % p e r d a y .

T o t e st t h e a c c e p t ab i l it y o f t h e e n d p r o d u c t w h o l e u n g u t t e d t u r b o t o f a c c e p ta b l es iz e w e r e d i s t r ib u t e d a m o n g s t t h e s t u d e n t s , t e c h n i c a l a n d a c a d e m i c s t a f f o f t h e U n i -v e r s it y . A n u m b e r o f w i ld c a u g h t f i s h we r e al s o o b t a in e d a n d s im i l a r l y d i s t r i b u t e d . Nop a r t i c u la r i n s t r u c t i o n s w e r e g i ve n o r e x p e r i m e n t c a r r ie d o u t s o t h a t t h i s p r o c e d u r ec a n n o t b e c l a i m e d t o h a v e a n y p a r t i c u l a r s ci e n ti f ic m e r i t . H o w e v e r , w i t h o u t e x c e p t i o ne v e r y o n e a g r e e d t h a t t h e t u r b o t w e r e o f e x c e l l e n t te x t u r e a n d t a s t e a n d n o d i s t i n c ti o nc o u l d b e m a d e b e t w e e n f a r m e d a n d w i l d c a u g h t f i s h .

H u s b a n d r y p r o b l e m s d u r i n g t h e f e e d i n g t ri al s w e r e r e la t i v el y f e w . T h e m o r t a l i t yr a te w a s o f t h e o r d e r o f 1 % w h i l s t a f u r t h e r 2 % d e v e l o p e d a d a r k p i g m e n t a t i o n a n db e c a m e b l i n d . A fe w o f t h e e x p e r i m e n t s h a d t o b e t e r m i n a t e d w h e n t h e r a p i d g r o w t ho f t h e f i s h l e d t o o v e r lo a d in g o f t h e f i l t e r b e d s ( T a b l e 5 ) a n d i n o n e p a r t i c u l a r c a s e am e c h a n i c a l p r o b l e m o c c u r r e d ( T a b l e 4 ) .

I n i t i a l ly s t o c k in g d e n s i ti e s w e r e l o w in t e r m s o f we ig h t y e t h ig h i n te r m s o fn u m b e r s . F o r e x a m p l e , a t t h e s t a rt o f th e f ir s t e x p e r i m e n t t h e r e w e r e 9 9 2 . 2 g o f1 0 - 2 0 g fi s h , 6 8 i n d iv id u a ls o f m e a n we ig h t 1 4 -6 g ( T a b l e 2 ) , i n Gr o u p A . T h i s c o r r e -s p o n d s t o a s t o c k in g d e n s i t y o f 2 - 6 k g m - 2 ( 1 7 4 f i s h m - 2 ) o r 1 3 -2 k g m - 3 ( 9 2 0 f i s h m - 3 ) .A t t h e e n d o f t h e f e e d i n g e x p e r i m e n t s , h o w e v e r , s t o c k i n g d e ns i ti e s w e r e h i g h i n te r m so f w e i g h t a n d l o w i n t e r m s o f n u m b e r . F o r e x a m p l e , a t t h e e n d o f t h e l a st e x p e r i m e n tt h e 8 5 - 1 0 0 g c a t e g o r y o f f is h i n G r o u p B h a d r e a c h e d a b i o m a s s o f 4 3 1 5 . 0 g , 1 7 i n di -v i d u al s o f m e a n w e i g h t 2 0 5 . 5 g ( T a b l e 5 ) . T h i s c o r r e s p o n d s t o a s t o c k i n g d e n s i t y o f1 1.7 k g m - 2 ( 4 6 f i sh m - 2 ) o r 5 7 .5 k g m - 3 ( 2 2 7 f i s h m - 3 ) . I n t e r m s o f t h e r e c i r c u l a t i n gs y s t e m s t h e m s e l v e s t h e m a x i m u m c a r r y i n g c a p a c i ti e s a c h i e v e d w e r e 1 0-7 k g m - 3 o fr e c i r c u la t i n g w a t e r a t a h y d r a u l i c l o a d i n g o f 3 6 m 3 m - 3 d a y -1 . W a te r q u a l i t y d a t a we r eo b t a i n e d s e p a r a te l y f o r e a c h r e c i r c u la t i n g s y s t e m a n d c o m b i n e d t o g iv e t h e m e a nc o n d i t i o n s p r e v ai li n g t h r o u g h o u t t h e f e e d i n g e x p e r i m e n t s ( F i gs 2 a n d 3 ). T h e p Hr e m a in e d i n t h e r e g io n o f 7 .0 -+ 0 .5 wh i l s t D .O . w a s i n e x c e s s o f 7 m g l i tr e - 1 o r 9 0 %s a t u r a t e d . U n i o n i z e d a m m o n i a l e v el s p r e s e n t i n t h e t a n k w a t e r w e r e o f t e n v i r t u a ll y


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GROWTH OF TURBOT IN RECIR CULATI NG SYSTEMS 31

r

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' ' o ' d o b ' ' '2 40 8 100 120 140Day s

Fig. 2. M e a n v a l u e s f o r t e m p e r a t u r e , s a l i n i t y , p H a n d d i s s o l v e d o x y g e n d u r i n g t h e f e e d i n g t r ia ls .

u n d e t e c t a b l e a n d w e r e n e v e r g r e a te r t h a n 4 x 1 0 4 m g l it r e - 1. N i t r i t e l e v e l s w e r e a l s ol o w b e i n g < 0 . 6 m g l it re -1 . N i t r at e s h o w e d a n i n it ia l sh a r p r ise w i t h m a x i m u m c o n c e n -t r a ti o n s o c c u r r i n g a t a b o u t d a y 2 0 . T h e s e s u b s e q u e n t l y d e c l in e d a n d a ft e r d a y 6 0 w e r ef a ir l y c o n s t a n t a n d i n t h e r e g i o n o f 1 0 0 m g l it r e - 1.

DISCUSSION

T h e r e su l ts o f t h e p r e s e n t w o r k i n d i ca t e t h a t y o u n g t u r b o t a c c e p t a r a ng e o f d i ff e r e n tf is h d i e t s p r o d u c i n g g o o d g r o w t h r a te s a n d c o n v e r s i o n e f f ic i e n c i e s w i t h n o si g n if ic a n t


10/12

32 M .G. POXTON, K. R . MURRAY, B. T . LINFOO T~1..

3 0

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& 2 ' 0 4 ' 0 d o 8 ' o 1 ; o 1 1 oDays

Fig. 3 . Mean values for unionized am mon ia, n i t r i te and ni t ra te dur ing the feeding t ria ls ,h e a l t h p r o b l e m s . O f t h e s p e c i es t e s t e d , s p r a t s a n d s a n d e e l s a p p e a r e d t o b e t h e m o s tp r o m i s i n g . T h e s e f is h f o rm p a r t o f t h e n a t u r a l d i e t o f t h e t u r b o t ( R a e a n d D e v l in ,1 9 7 2 ) , a n d a t 1 6 C f e e d i n g r a t e s c a n b e m a i n t a i n e d a t a h i g h l e v e l ( 4 - 5 % d a y - l ) . I tis w o r t h s t re s s in g t h e i m p o r t a n c e o f p r e s e n t i n g n o t o n l y t h e r i g h t si ze b u t a l s o a s u it -a b l e s h a p e o f p r e y t o t h e f i s h . S p r a t s a n d s a n d e e l s f o r m a l a rg e p a r t o f t h e i n d u s t r i a lc a t c h i n t h e N o r t h S e a . T h e y a re a v a i la b l e f r es h f o r c o n s i d e r a b l e p e r i o d s o f t h e y e a ra n d i t s h o u l d b e p o s s i b l e t o g r a d e t h e m i n t o a p p r o p r i a t e s iz e s f o r p a r t i c u l a r g r o u p s o ft u r b o t . T h e p r e s e n t a t i o n o f w h o l e f is h c o n s i d e r a b ly im p r o v e s t a n k h y g i e n e a s c h o p p e dr a t i o n s c a n l e a d t o t h e b u i l d u p o f a f i lm o f l i p id o n t h e s u r fa c e o f t h e w a t e r i f t h ef e e d i s n o t a d e q u a t e l y w a s h e d . V e r y l i tt l e w a s t a g e o c c u r r e d w i t h t h e u s e o f s p r a t s a n ds a n d e e l s a n d t h e r e w e r e n o a c c e p t a b i l i t y p r o b l e m s . I n d e e d , t h e i n t r o d u c t i o n o f w e td i e t s l e d t o a n o t i c e a b l e i n c r e a s e i n f e e d i n g r a t e s . T h i s a l s o o c c u r r e d w h e n w e t d i e t sw e r e c h a n g e d . T h e m o s t e c o n o m i c a n d c o n v e n i e n t s t r a t e g y fo r f e e d in g m a y b e t o w e a nt h e f i s h f r o m t h e i r m o i s t p e l l e t d i e t a t a r o u n d t h e 1 0 g si ze o n t o s m a l l s p r a t s . A tg r o w t h r a t es a c h i e v e d i n t h e se e x p e r i m e n t s o f 2 % d a y - 1 i t w i l l t a k e i n t h e r e g i o n o f2 0 0 d a y s t o o n g r o w f i sh w h i c h w h e n g u t t e d w i ll b e in t h e 5 0 0 g c a t e g o r y , a s i ze w h i c hm a y b e s u i t a b l e f o r m a r k e t i n g ( K e r r , 1 9 7 6 ).


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GROWTH OF TURBOT IN RECIRCULATING SYSTEMS 33

I t i s r e c o m m e n d e d t h a t t h e d i e t o f t h e f is h c a n b e c h a n g e d a t f r e q u e n t i n t e rv a l sdu r ing t he ong row ing s t age. I t is pos s ib l e t ha t a pa r t i cu l a r f oo d f i sh may be de f i c i en ti n ce r t a in e s sen t i a l v i tamins whe rea s i t is un l i ke ly t h a t d i f f e r en t spec i e s o f f ood f i shwou ld a l l be l a ck ing t he s ame e s sen t i a l nu t r i t i ona l e l emen t s . Th i s pos s ib i l i t y cou ld o fcou r se be c i r cumven ted by g iv ing an occas iona l f e ed o f a v i t amin pe l l e t . La rge sp ra t sgave pa r t i cu l a r l y good g rowth r a t e s a f a c to r wh ich may we l l r e su l t f r om the i r l owwa te r co n t en t (Tab l e 1 ). Ho wev e r , sp r a t s a r e ' f a t t y ' fi sh and Ad ron e t a l . ( 1 9 7 6 ) h a v erepo r t ed t ha t a s d i e t a ry l i p id l eve ls i nc rea se so t oo does t he l i p id con t e n t o f t he f i shp roduced . S ince t u rbo t a r e p r i zed fo r t he i r f l avou r t he i r ma rke t ab i l i t y cou ld i n t heo rybe impa i r ed . I n t he se and subseq uen t expe r imen t s , how eve r , in wh ich t he f i sh haveb e e n e a t e n , n o e v i d e nc e o f s u c h a p r o b l e m h a s e ve r b ee n f o u n d .

Due t o t he h igh was tage and g rea t e r cos t o f wh i t i ng t oge the r w i th t he i nconven ienceo f hav ing t o cho p up l a rge f i sh w i th t he a s soc i a t ed t ank hyg iene p rob l em s , i t seemsthe i r u se fu lne s s m ay be l im i t ed . T hey wo u ld be o f g r ea t e s t va lue a s a f i na l f oo d p r io rto marke t i ng a s wh i t i ng have a h ighe r p ro t e in and l ower l i p id con t en t t han sp ra t s . Ofcou r se o the r i ndus t r ia l gado id f ish such a s t he Norw ay Pou t , T r i s o p t e r u s e s m a r k i i(N i l s son ) and B lue wh i t i ng , M i c r o m e s i s t iu s p o u t a s s o u (R i s so ) may we l l be ve ry u se fu lsubs t i t u t e s fo r wh i t i ng .

The r ec i r cu l a ti ng sys t em s p roved t o be ex t r e m e ly succes sfu l , ma in t a in ing a r e li ab lee n v i r o n m e n t i n w h i c h t h e f is h c o u l d b e g r o w n . T h e o n l y p r o b l e m t o b e e x p e r i e n c e do c c u r r e d w i t h t h e u se o f t h e m o i s t p el le t s, w h i c h t e n d e d t o b r e a k u p i f l e f t u n e a t e nin t h e t a n k s a n d b e c a r ri e d f o r w a r d t o t h e t r e a t m e n t u n i ts . A m o r e e f f ec t iv e m e t h o d o fm e c h a n i c a l f i l t r a ti o n o r a s e d i m e n t a t i o n s y s t e m w o u l d n e e d t o b e d ev e l o p e d i f t h ist y p e o f f o o d w e r e i n c o n s t a n t u s e i n t h e s y s t e m s d e sc r ib e d .

ACKNOWLEDGEMENTST h i s w o r k w a s s u p p o r t e d b o t h b y H e r i o t - W a t t U n i v e r s it y a n d b y th e S c i en c e R e s e a r c hCounc i l , M ar ine Tec hno logy D i r ec to r a t e . I t a lso r e l ied on t he sup por t o f va r ious UKf i sh f a rm ing o rgan i za t i ons . T he au tho r s wo u ld e spec i a l ly l i ke t o t han k t he Br i t ishW h i te F i s h A u t h o r i t y f o r t h e ir h e lp a n d e n c o u r a g e m e n t a n d i n p a rt i c u la r f o r s u p p l y i n gwi ld t u rbo t and mo i s t pe l l e t d i e t (WFA 7 ) .

REFERENCESAdron, J., Blair, A., Cowey, C. B. & Shanks, A. M, (1976). Ef fects of dietary energy source ongrowth, feed conversion and body composition of turbot (Scophthalmus maximus L.). Aqua-culture, 7, 125-32.Bendschneider, K. & Robinson, R. J. (1952). A new spectrophotome tric metho d for the determi-nation of nitrite in sea water. J. Mar. Res., 11, 87-96.Hull, S. T. & Edwards , R. D, (1979). Progress in farming turbot , Scophthalmus maximus, infloating sea cages. In: Advances in Aquaculture, ed. T. V. R. Pillay and W. A. Dill. Farnham,

Surrey, Fishing News Books, pp. 466 -72.


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J o n e s , A . ( 1 9 7 2 ) . M a r i n e fi s h f a r m i n g ; an e x a m i n a t i o n o f t h e f a c t o r s t o b e c o n s i d e r e d in t h e c h o i c eof spec ies . Lab. Leafl . Fish Lab. Low esto f t , N .S . , 2 4 , p p . 1 6 .K e r r , N . M . ( 1976 ) . R e c e n t t e c hn ic a l a dva nc e s i n m a ~ ine f l a t f i sh f a r m ing . Proc. R. Soc. Edin. (B) ,7 5 , 2 6 3 - 7 0 .K i n n e , O . ( 1 9 7 6 ) . C u l t i v a t i o n o f m a r i n e o r g a n is m s : w a t e r - q u a l it y m a n a g e m e n t a n d te c h n o l o g y . I n :Marine ecology - 3 , e d . O . K i n n e , L o n d o n , J o h n W i le y a n d S o n s , p p . 1 9 - 3 0 0 .M a y o , R . D . ( 1 9 7 9 ) . A t e c h n i c a l a n d e c o n o m i c r e v ie w o f t h e u s e o f r e c o n d i t i o n e d w a t e r i n a q u a -c u l tu r e . I n : Adv anc e s i n Aquac u l t u re , e d . T . V . R . P i l la y a nd W . A . D i l l . F a r nh a m , S u r r e y ,F i s h i n g N e w s B o o k s , p p . 5 0 8 - 2 0 .M u r r a y , J . & B u r t , J. R . ( 1 9 6 9 ) . T h e c o m p o s i t i o n o f f i sh . A d v i s o r y N o t e . T orry L ab . Abe rde e n ,38, p . 16 .P o x to n , M . G . , M ur r a y , K . R . , L in f o o t , B . T . & P oo le y , A . B . W . (1981 ) . T he de s ign a nd pe r -f o r m a n c e o f b i o l o g i c a l f i l t e r s i n a n e x p e r i m e n t a l m a r i c u l t u r e f a c i l i t y . I n : Proceedings o f theW orm Sy m pos i um on Aqu ac u l t u re i n He a t e d E f f l ue n t s & Re c i r c u la t i on , Sys te ms, vol. I , ed.K . T ie w s , B e r l i n , pp . 3 70 - 82 .

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