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, 4 q u a c u l ru e a [ E n g i n e e r i n g 5 1 9 ~ 6 3 3 - 4 7

R e v i e w o n E x p e r i m e n t s o n U s e o f Z o o p l a n k t o n a s F o o din S a i m o n i d S m o l t P r o d u c t i o n

J e n s C h r . H o l mI n s t it u t e o f F i s h e r i e s B i o l o g y , U n i v c r s i t v o f B c rg c n . N - 5 0 1 1 B e r g e n N o r d n e s , N o r w a y

A B S T R A C T.Vine e_ff )er iments carr ied ou t in the pe ri od 1981 - 1983 in a coas ta l laken ea r B er g en , N o r w a y , a r e t h e b a s i s f o r t h is d i s cu s s io t t o f f e ed in g o fA t / a n t i c s a h n o n o n l iv e f r e s h w a t e r z o o p l t m k t o n . F a c to r s d i s c u s s e d a r ed i f f eren t enc losur e types , d iurn a l var ia t ion an d curren t veloc ity, inc lud-ing a rev iew o f se lec ted l it era ture . Th e a im was to eva lua te to wh a td eg r ee z o o p la n k to n m a y b e o .! c e r ra ip t imp o r ta n c e a s s ta r t- a n ds t t p p l e m en t - f o o d f o r s a lm o n id s itz th e fr e s h w a te r s ta ge .

I N T R O D U C T I O NThe use o f l ive zoop lank ton as f i sh food , pa r t i cu la r ly fo r the ea r lys t a g e s , i s a w e l l - k n o w n t e c h n i q u e . V a r i o u s c o r e g o n i d s h a v e b e e nr e a r e d b y u s in g li v e f r e s h w a t e r z o o p l a n k t o n a t t r a c t e d b y a r t if i c i a l l ig h t(J~iger an d N el len , 1980) . Pau l e t a l . ( 1 9 7 6 ) r e a r e d c h u m s a l m o n f r y( O n c o r h y n c h u s k e t a ) i n a n a r t i f i c i a l u p w e l l i n g p o n d o n d i a t o m s a n d ac o p e p o d , A c a r t i c i c l a u s i . U r q u a h a r t a n d B a r n a r d ( 1 9 7 9 ) r e a r e d p i n ks a l m o n f r y ( O n c o r h y n c h u s g o r b u s c h a ) m a i n l y o n c a l a n o i d c o p e p o d st r a n s p o r t e d i n to t h e p e n b y t id a l c u rr e n t s . A r n e m o e t a l . ( 1 9 8 0 )o b s e r v e d A t l a n t i c f r y s t a r t - f e e d i n g o n l a k e z o o p l a n k t o n . A t l a n t i cs a l m o n f ry r e a r i n g w i th li ve z o o p l a n k t o n e x p e r i m e n t s a r e r e p o r t e d b yH o l m e t a l . ( 1 9 8 2 ) , Pepper et a l. ( 1 9 8 3 ) , R e i n e r t s e n et a l . ( 1 9 8 4 ) a n dH o l m ( 1 9 8 5 a ,b ) . I n N o r w a y , l a k e z o o p l a n k t o n h a v e n o t b e e n u t i l i z e da s f o o d i n s a l m o n i d c u l t u r e , e x c e p t i n s o m e e x p e r i m e n t s . A f e w s a l m o ns m o l t f a r m e r s , u s i n g n e t p e n s i n l a k e s , h a v e w i t h o u t d o u b t m a d e u s e o fliv e z o o p l a n k t o n u n i n t e n t i o n a l l y .S i n c e 1 9 7 8 , e x p e r i m e n t s h a v e b e e n c a r r i e d o u t i n K v e r n a v a t n e t . ac o a s ta l l a k e a b o u t 4 0 k m s o u t h o f B e r g e n , i n i t ia l ly b y th e D e p a r t m e n to f A q u a c u l t u r e . I n s t i t u t e o f M a r i n e R e s e a r c h . T h i s p a p e r a i m s t o g i v e

3 3,4quacul turul k . t t~. ineer in.~ 0 1 4 4 - 8 6 1 ) 9 $ 6 S I ) 3 _ 5 0 - - ~ E l s e v i e r A w ~ t i ed S c i c n c c


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3 4 J . C . Holmt h e p r e s e n t s ta g e o f k n o w l e d g e i n p r a c t ic a l t e c h n i q u e s a n d a s p e c t s o fz o o p l a n k t o n a s f o o d i n s a l m o n i d c u l t u r e .

M A T E R I A L A N D M E T H O D ST h e e x p e r i m e n t s c a r r i e d o u t in K v e r n a v a t n e t , r e p o r t e d h e r e , s t a r te d i n1 98 1 a n d c o n t i n u e d u n t i l 1 9 8 3 . F i v e d i f f e r e n t ty p e s o f f i s h f a r m i n gu n i t s w e r e u s e d :

(i) A n e x p e r i m e n t a l f l o a t in g n e t (5 m m s t r e t c h e d m e s h e s ) c a g e s( 3 .0 m -~) w i t h a r e c t a n g u l a r b o t t o m ( F i g . 1). Z o o p l a n k t o n w e r ed e l i v e r e d t o t h e fi sh b y a n i n d u c e d c u r r e n t . A d e t a i le d d e s c r i p -t io n o f t h e e x p e r i m e n t a l u s e o f s u c h c a g e s is g i v e n b y H o l m a n dM o i l e r ( 11 98 4 );

( ii) c y l i n d r i c a l e n c l o s u r e s ( p l a s t i c c o a t e d t e x t i l e 1"5 m -~) w i t h as m a l l b o t t o m o u t le t . W a t e r c o n t a i n i n g z o o p l a n k t o n w a sd e l i v e r e d b y a l o w p r e s s u r e p u m p ( F ig . 2 );

{ iii ) s m a l l c y l i n d r i c a l n e t c a g e s ( 1- 0 m ,~) w h e r e w a t e r w i t h z o o p l a n k t o nw a s d e l i v e r e d b y a lo w p r e s s u r e p u m p ( F ig . 3 );( iv ) s t a r t - f e e d i n g s q u a r e t r a y s (0 .3 m ~ ), w h e r e w a t e r c o n t a i n i n g z o o -

p l a n k t o n w a s c a r r ie d t h r o u g h p i p e l in e s . S u r fa c e d r a i n a g e in t h ec e n t e r o f t h e t ra y . F l o w r a t e : 0 - 5 - 1 - 5 l it r e s-~ :

%-. i %~,%%%% % ~. . , .z , . - .z , % .~

F i g . 1 . E x p e r i m e n t a l f l o a t i n g n e t c a g e , 3 '{ } n r~ : a r r o w s i n d i c a t e w a t e r s u r f a c e l e v e l.D e p t h 1"5 m , l e n g t h 2 -( } m . w i d t h l-O m .


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Revie w: : .oopian kton as fo od in sal m on id srno!t pr~oduction 3 5iv c o m m e r c i a l s q u a r e n e t p e n s ( 4 0 m 3); z o o p l a n k t o n w a s d e l i v e r e d

t h r o u g h o n e o f t h e p e n w a l ls (a r e a o f 1 0 m : ) t o t h e f is h b v a ni n d u c e d c u r r e n t , v a r y i n g b e tv , 'e e n 0 .5 a n d 8 c m s -L M e s h s iz e o ft l m m ( st re t c h ed ) .

I n a d d i t i o n . A t l a n t i c s a l m o n a n d r a i n b o w t r o u t (Salmo gairdneri :e s c a p e d o r r e l e a s e d f r o m t h e c o m m e r c i a l f i sh f a r m i n t h e la k e h a v eb e e n s a m p l e d f o r g r o w t h a n d c o n s u m p t i o n e s t im a t e s s in c e 1 9 8 1. C o m -m e r c i a l c a g e c u l t u r e in K v e r n a v a t n e t s ta r t e d in 1 9 7 9 , a n d , si n c e 1 9 80 .o b s e r v a t i o n s h a v e b e e n m a d e t o d e s c r i b e c o m b i n e d o r o b l i g a t e z o o -p l a n k t o n / d r y p e l l e t f e e d in g .

N a t ur al c o n c e n t r a t io n s o f z o o p l a n k t o n w e r e p u m p e d o r f l o w e d i nt ot he un i t s . T he cage w a l l s i n t ypes ( i i ) and ( i i i ) , and t he ou t l e t f i l t e r s i nt y p e ( i v ) , r e p r e s e n t e d b a r r i e r s f o r t h e z o o p l a n k t o n . A c o n c e n t r a t i n ge f f e c t w a s o b s e r v e d w h e n u s i n g l o w w a t e r f l o w r a t e s o v e r t h e f i l t e r i n ga r eas .

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F i ll . 2 . C y l i n d r i c a l e n c l o s u r e , 1 '5 m -::a r r o w s i n d i c a t e w a t e r s u r f a c e l e v e l .M e s h c o v e r e d b o t t o m o u t le t ( 5 m m

s t r e t c h e d m e s h e s ) .


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S k e t c h o f p r i n c i p a l c x p c r i m c n t a l d e s i ,m f r o m H a n s c n a n d H o l m ( 1 9 8 lP l a n k t o n n e t w a l l s .

T h e e x p e r i m e n t a l u n i t s w e r e m o s t l y s t o c k e d w i t h a l o w d e n s i t y o ffis h, p r o v i d e d w i t h su f f ic i e n t f e e d i n g c o n d i t i o n s . F i s h h a t c h e d t h es a m e y e a r o r y e a r l i n g s i r i s h h a t c h e d t h e y e a r b e f o r e ) w e r e u s e d i n at o ta l o f n i n e e x p e r i m e n t s , o f w h i c h six a r e o u t l i n e d i n T a b l e 1. I n t h em a j o r i t y o f t h e e x p e r i m e n t s , b o t h t h e o f f e r e d z o o p l a n k t o n a n ds t o m a c h c o n t e n t s w e r e m o n i t o r e d . F o r e s t i m a t i n g t h e r e la t io n b e t w e e ns t o m a c h f u l ln e s s ( a c c o r d i n g t o B a l l ( 1 96 1 )) e x p r e s s e d a s n u m b e r s f r o m0 ( e m p t y ) t o 5 ( m a x i m u m f u l l n e s s ) a n d n u m b e r o f z o o p l a n k t o no r g a n i s m s f o u n d i n t h e s t o m a c h c o n t e n t , 101 s a l m o n y e a r l i n g s ( fo r kl e n g th v a r ie d b e t w e e n 6 4 a n d 118 r am ) w e r e s a m p l e d f r o m a n e x p e r i-m e n t w i t h z o o p l a n k t o n a s f o o d r e p o r t e d b y H o l m a n d M ~ a lle r ( 1 98 4 ).T h e f o l l o w i n g e q u a t i o n w a s f it te d t o t h e d a t a ( r = 0 "9 8 !:

P = F L~ I0 ,3 32 7(B ): + 0 - 0 9 7 B + 0 . 0 0 7 1 )w h e r e P is t h e n u m b e r o f z o o p l a n k t o n ( n e a rl y 1 0 0 % D aphn ia longi-spina) f o u n d in a s i n g l e s t o m a c h , F L is t h e i n d i v i d u a l f is h f o r k l e n g t ha n d B is t h e s t o m a c h f u ll n es s . T h i s e q u a t i o n is u s e d w h e n m o n i t o r i n gd i u r n a l v a r ia t io n in th e s a lm o n ' s c o n s u m p t i o n o f Daphnia.


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s t o m a c h c o n t e n t sn o t e x a m i n e dPosit ive gro~vth rate

e l e c t iv i t y o b s e r v e d .b o t h o n s p e c i e san d s i ze lev e l( H o l m a n d M o i l e r ,1 9 8 4

P o s i t iv e g ro w th ra t e ,e l e c t iv i t y o b s e r v e do n sp ec ies l ev e lP o s i t iv e g ro w th ra t e ,n o o b v i o u se l e c t iv i t y ! H o l m etal.. 19,.


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38 J. C Holrnin to the enc losures . Surpr i s ing ly , in exper iment No . 1 , At lan t ic sa lmona lev ins s ta rved to dea th in de f iance o f a foo tba l l - l ike pa tch o f B. longi -s p i na i n t h e c e n t e r o f th e t r a y . T h e p a t c h w a s e a s i ly d e s t r o y e d b ys e t ti n g u p a h i g h e r w a t e r e x c h a n g e . I m m e d i a t e l y a f t e r it s d i s p e r s i o n t h er e m a i n i n g a l e v i n s s t a r t e d t o e a t.T h e r e s u lt s i n d i c a t e t h a t a n i n c r e a s i n g c u r r e n t v e l o c i ty w il l d e c r e a s et h e s p e c i e s s e l e c t i o n . A c e r t a i n c u r r e n t v e l o c i t y i s n e c e s s a r y t o p r e v e n tp a t c h i n g o f s o m e o f t h e z o o p l a n k t o n s p e c i es . C o p e p o d s s e e m e d t om a i n t a i n t h e i r p a t c h e s i n h i g h e r c u r r e n t v e l o c i t i e s t h a n d i d c l a d o -c e r a n s .D iu rn a l varia tion in zoop lan k ton f eed in gT h r e e f e e d i n g e x p e r i m e n t s h a v e b e e n c o n d u c t e d t o i l l u s t r a t e d i u r n a lv a r i a t i o n o f A t l a n t i c s a l m o n f e e d i n g o n z o o p l a n k t o n . T h e f i r s t t w oe x p e r i m e n t s ( N o s 7 a n d 8 ) d e s c r i b e f e e d in g o n z o o p l a n k t o n o n l y , t h et h i r d ( N o . 9 ) c o m b i n e d f e e d i n g o n z o o p l a n k t o n a n d c o m m e r c i a l d r yf o o d . R e s u l t s f r o m t h e o b l i g a t e z o o p l a n k t o n f e e d i n g e x p e r i m e n t a r egiven in Figs 4 (N o. 7) and 5 (No. 8). Ty pe ( i) cages we re used . Th e offert o t h e s a l m o n a n d t h e i r c o n s u m p t i o n f o r e x p e r i m e n t N o . 7 a r e g i v e n i nT a b l e 2 . A t t h e e n d o f J u l y, t h e a m o u n t o f z o o p l a n k t o n o f f e re d w a sp o o r e r t h a n in J u n e , a n d o b s e r v e d c o n s u m p t i o n w a s si g n i fi c a n tl y l o w e r( e x p e r i m e n t N o . 8 ). F o o d s e l e c ti o n i n e x p e r i m e n t N o . 7 s h o w e d a d i u r n a lvar ia t ion (Tab le 2 ) . B o s m i n a l o n g i s p i n a s h o w e d u p t o b e n e g a t i v e l yse lec ted in the pe r iod excep t fo r the 1200 h observa t ion . Food se lec t ionex pre ssed as Iv lev 's inde x of e lect iv i ty ( Iv lev. 1961) was + 0-1 (s l ight lypos i t ive se lec t ion) a t th i s t ime , and decreased to -0 -5 (nega t ive se lec -t ion) a t midnight . D a p h n i a became a pos i t ive index o f e lec t iv i tv fo r a l lfour pe r iods , v a ry ing be tw een + 0-76 ( 1200 h ) and + 0 .87 (2000 h ).Sam pl ing in a type (v ) cage wi th a h igh wate r cur r en t inpu t (exper im entN o . 9 ) w a s c o n d u c t e d i n 1 9 8 3 . T h e r e s u lt s ar e p r e s e n t e d i n T a b l e 3 .Z o o p l a n k t o n f e e d in g o c c u r r e d m o s t l y d u r i n g t h e d a r k p e r i o d w h e n a u to -m a t e d f e e d i n g d i d n o t o c c u r . D u r i n g t h e li g ht p e r i o d d w f o o d p e l l e tss e e m e d t o d o m i n a t e .

D I S C U S S I O NM o t t r a m ( 1 9 2 8 a , b ) a n d M u r d o c h ( 1 9 2 8 ) w e r e t w o o f th e f ir s t a u t h o r s t od i s c u s s t h e u s e a n d c u l t i v a t i o n o f D a p h n i a f o r t h e p u r p o s e o f f e e d i n gtrout f ry ' , S a h n o t r u t m . Severa l advan tages o f the use o f such l ive p reyh a v e b e e n p o i n t e d o u t. S o m e o f t h e s e , r e le v a n t to A t l a n t i c sa l m o n p r o -


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d u c t i o n , a r e g i v e n b y H o l m a n d M o i l e r ( 1 9 8 4 ) . A r n e m o ( 1 9 7 5 ) f o u n dbe t t er growt h in pond ( sa lmon parr f eed ing on nat ura l f ood i t ems) t hanin c o n v e n t i o n a l f is h f a rm s .

W h e n u t i l i z i n g l i v e z o o p l a n k t o n a s a f o o d f o r y o u n g s t a g e s o fsa lmonids , i t i s impor t ant t o co l l e c t t h i s f rom t hat par t o f t he wat erm a s s e s w h i c h p r o v i d e t h e o p t i m a l o f f e r . T h i s r e q u i r e s f i n d i n g a c t u a ll o c a li ti e s b y f o l l o w i n g a s p e c i a l s a m p l i n g p r o g r a m m e t o cla ri~ " w h e r e t h e


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D i u r n a l v a r i a t io n i n z o o p l a n k t o n f e e d i n ~ ~ ' "~ -, . 4 - , ~ J u l y 19 8 1 ( E x p e r i m e n t N o . 8 :.:a) and ( b as for Fig. 4.

a c t u a l p r e y s p e c i e s a r e , a n d w h e r e t h e y o c c u r in s u i t a b l e d e n s i t ie s b o t h i nt i m e a n d s p a c e . S u c h a p r o g r a m m e w i ll a l so g iv e i n f o r m a t i o n o n w h e ns ta r t f e e d i n g s h o u l d o c c u r , a n d h a tc h er y ' s c h e d u l e s c a n t h e n b e s e t u p t oa c h i e v e t h i s .C u r r e n t v e l o c i t y w h e n p r e s e n t i n g l iv e z o o p l a n k t o n t o t h e f is hI rv in e a n d N o r t h c o t e ( 1 9 8 3 ) c o n c l u d e t h at t h e r e i s a n e e d f or f u rt h ere x p e r i m e n t a l f e e d i n g s t u d ie s o f st r e a m f i s h e s b e f o r e a m o d e l c a n b e


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Review." : .oop tank , .on o.~] b o d i n s a h . , o n i d s m o l t p r o d u c t i o n + iT A B L E 2

F o o d S e l e c t i o n o f A t l a n t ic S a l m o n Y e a r li n gs . L a k e K v e r n a v a m e t , 2 6 - 2 7 J u n e l g S ii E x p e r i m e n t N o . 7} m e a n v a l u e s o f o f f e r b a s e d o n d ri ft s a m p l e s t a k e n a t 1 - 0 a n d

1 5 m d e p t h s . 1 -0 m o u t f r o m t h e c a g e w a l l sSpe c ie .+ g ro up O b s e r " e d d i s t r i b u t i o n +;, ~ y m d in cZ ~-erStomach.+

1200 h 20 00 h 24 '. )0 17 08 00 hD u p h n i a l o n g i s p i n aB o s m i n a l o n g L v p b mD i a p h a t t o s o m a b r a c ' h v t + r t t r nH o l o p e d i . m g i b b e r u . "C a l a n o i d c o p e p o d sC y c l o p o id c o p c p o d sM e a n D a p h n i a l e n g t h s r a m )R e l a t iv e n u m b e r o f z o o -

p l a n k t o n p r e s e n t in t h ec t , r r c n t l e a d i n g i n t o t h ec a g e s "

8 . 9 . . 6 9 . _. 0 ~ .5 1 .6 . . . . - , . - , . . . . . .,0 ] . ~ ' , l ( )' fi 8 2 ' 83 6 ' 8 ' 4 5 ' 2 4 6 - 9 2 6 - 7 5 4 - 8 ' 1 7" 0 5 6 7 / 3 0 4

0- 8 + 0- 0 0 - 0 0 + 0 L-O 0 . l I ) . 6 / ( ) . 00 - 7 ' i F 0 +).++ + + )- ) 0 ' ( ) 0 - 0 0 - 4 q )- ~)

" l - 6 3 ' I I S " ~ 0 - 4 I 0 6 , 0 . l ,- ~' . . . . " .3 3 . 1 ~ ).1 2 8 . 9 ( ) .I 2 2 . 1 0 . () 1 8 - 8 / 0 - 10 . 7 S .' 1 . 6 8 _ t ) . 8 1 < 1 - 6 3 1 . 0 2 ' . , 7 " . . . .) . 9 ~ l - 6 S

1-0 I '3 2"4 t '{ )

" M e a n n u m b c r f r o m 1 2 0 0 h d r i f t s a m p l c s l ( ) m i n s c t t o 1 - 0 .

d e v e l o p e d i n c o r p o r a t i n g r e le v a n t in p u t s fr o m l a k e p a r a m e t e r s , b u t a l s os t r e s s i n g p r o c e s s e s a p p l i c a b l e t o t h e s t r e a m e n v i r o n m e n t , l r v i n e a n dN o r t h c o t e s u g g e s t th a t p r e y b o d y m o v e m e n t s h o u l d b e u s ed a s o n e o ft h e i n p u t s t o e x p l a i n p r e d a t o r s e l e c t i v i t y i n s t r e a m f e e d i n g f i s h e s .R i m m e r a n d P o w e r 1 9 7 8 ) , d e a l in g w i th th e f e e d i n g r e s p o n s e o f A t l a n t ics a l m o n a l e v i n s i n f l o w i n g a n d s t i l l w a t e r , c o n c l u d e t h a t f o o d n e e d n o t b ec a r r ie d in a w a t e r c u r r e n t , b u t t h a t m o t i o n o f t h e p r e y i s n e c e s s a W . T h ep r e y m o t i o n c a n b e p r o v i d e d b y w a t e r c u r r e n t o r b y th e p r ey .

P r e y a c ti v it y a l o n e m a y b e s u f f i c i e n t t o e li c it s u c c e s s f u l f e e d i n g . Y o u n gS o c k e y e s a l m o n (On corh ynchus ne rka ) e n t e r l a k e s v e ~ , s o o n a f t e re m e r g e n c e a n d f e e d o n z o o p l a n k t o n in a s ti ll -w a t e r e n v i r o n m e n t( M c C a r t . 1 9 6 7 ) .

M o r f i s o n ( 1 9 8 3 ) a n a l y z e d t h e s t o m a c h c o n t e n t s o f y e ar s 0 + a n d 1 +A t l a n t i c s a l m o n p a r r i n t r o d u c e d i n t o a S c o t t i s h h i l l l o c h . L a b o r a t o r - ve x p e r i m e n t s i n d i c a t e d t h at c o p e p o d s w e r e d i ff ic u lt to c a p tu r e a n d t h a td a p h n i d s p e c i e s w e r e t h e o r g a n i s m s m o s t f r e q u e n t l y s e l e c te d , e v e n w h e nl ar g er i n d iv i d u a l s o f t h e s e s p e c ie s w e r e r e m o v e d f r o m t h e e n v i r o n m e n t .

O u r p r e s e n t r es u lt s ( e x p e r i m e n t N o s 1 - 6 ) o u t l i n e c u r r e n t v e l o c it y a sa n i m p o r t a n t t o o l r e g u l a t i n g s e l e c t i v e z o o p l a n k t o n f e e d i n g b y A t l a n t i c


10/15

' "~ J . C . H o l mT A B L E 3Outl ines of an Exp erime nt w ith Atlantic Salmon Yearlings Feeding on Zoop lankto n,19-2 0 July 1983 Experim ent No. 9 ;- '

T i m e o r ' d ay16{,~) 20~X) 2 4Lw,) 04(X ~ 06'00

Mean num ber s of zo o- t0 (7 i 32 (9 ) 1.08 i3i 183 14}plankton (mainlyD a p h n i a l o n g z s p t n a ~found in s tomac hsM ean values of Bali's index 3-9 (0-8i 4.1 (0-7) 3'5 (0-4~ 3'i) i 1.-0Theore t ica l numbers o f 548 604 445 332zoopla nkton i f a ll dryfood w ere replacedwith zoo plankton ~Est imated mean per cent 2 5 24 55values o f zo op lank tonpresent in the s tomac hsibased on volume) '

81 12)

4"3,0"7')66 2

12

"Each value repr esen ts a sample of 211 fish, mean fork leng th = 100-7 (0.2 ram), takenfrom a cage type (v) with hig h input o f zooplankton, confidence limits of 95% aregiven in parentheses. Au tom ated feeding w ith dry food pellets occ urred every 5 rainbetw een 05(1t) and 23 00 h.~Calculated with ti le equa tion given in the section "M aterials a nd M ethod s' .' 100 x mean nu mb ers of zooplank ton found in s tomac hs (row 1 /theoret ical numbe rsof zoopla nkton (row 3).

s a l m o n . B o t h t h e p r e y d e n s i t i e s a n d t h ei r a b il i t y o f d e t e c t i n g a n d e v e n -t u a l l y e s c a p i n g ( s e e D r e n n e r e t a l . , 1 9 7 8) f r o m t h e a t t a c k in g s a l m o n a r eb e l i e v e d t o b e in f l u e n c e d b y t h e c u r r e n t v e l o c it y . T h e b e h a v i o u r a l i n te r -a c t io n s b e t w e e n d i f f e r e n t s p e c ie s o f z o o p l a n k t o n a n d s a l m o n a r e ani m p o r t a n t t o p ic f o r f u r th e r w o r k . P r e s e n t k n o w l e d g e f r o m t h eK v e r n a v a t n e t s t u d ie s i s p a r t l y p r e s e n t e d b y H o l m a n d M o i l e r ( 19 8 4 ) a ndH o l m ( 1 9 8 5 a , b ) .

R e a r i n g e n c l o s u r e s s h o u l d b e c o n s t r u c t e d in s u c h a w a y th a t a f lo w -in g e n v i r o n m e n t c a n b e p r o v i d e d . I t is a l s o i m p o r t a n t t o m a k e a d j u s t -a b l e c o n s t r u c t i o n s , e s p e c i a l l y o f i n le t p i p e s a n d o u t l e t f i l te r s, toa c h i e v e m a x i m u m r e g u l a t in g f l e x ib i li ty .

H o w e v e r , a h ig h c u r r e n t v e l o c i t y w il l p r o b a b l y i n c r e a s e t h e s a l m o np a r r 's c a p t u r e p r o b a b i l i t y w h e n p r e y i n g o n th e f a s t m o v i n g c o p e p o d s .


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R e v i ew : z o o p l a n k t o n a s . lb o d it: s a ! m o n i d s m o h p r o & , c r i o n -~3For many fish farmers, this advantage is countered by the increaseddanger of tapeworm parasites in troduced by the copepods. Concentra-tions of zooplankton in the enclosures must be monitored, and non-popular food organisms such as copepods should not be atlowed toconcentrate too much.Di u rn a l v a r ia t io n i n zo o p l a n k t o n f eed i n gUnlike a normal dry-food based feeding regime, stomach contents inJune (experiment No. 7) reached a maximum level at midnight. In addi-tion. the number of zooplankton and relative occurrence of Daphnialongispina presented to the salmon reached a maximum in the sameperiod.When feeding on natural available zooplankton in July iexperimentNo. 8), taken from the upper water masses, a high feeding activity seemsto occur at sunrise and sunset. This may be based on a combination oflight intensity, zooplankton availability and fish satiation.Observing Sockeye salmon, McCart (1967) found highest feedingactivity between the hours of 12.00 and 20.00. Allen (1981 ~. describingBrook trout (Salve l inus font inal i s ) feeding activity in June and July,observed the maximum level between 18.00 and 20.00 h. Arnemo(1975) found highest zooplankton occurrence in Atlantic salmonstomach samples from darker periods; lowest consumption was found athighest light intensities.Fish color vision is optimal at high levels of light intensities Lythgoe.1966), and an increase of the best pigmented of the two cladocerans,B o s m i n a , should be the result. This was observed in June experimentNo. 7).When monitoring conventional dry-fed groups of Atlantic salmon,maximum zooplankton feeding occurred in the darkest period; thesalmon seems to supplement the dry-food diet with zooplankton mainlywhen dry food is not available and zooplankton is available due tovertical migrations (experiment No. 9). Fish were sampled randomly inthe actual cage, and can be recognized as representative of a total of8000 salmon parr present in this cage. Most of the other cages in thefishfarm got a lower input of zooplankton. A zooplankton supplement,specially for the youngest stages, can represent an important food sourceof high nutritional value, and this can be provided by transferring the fishbetween different cages following certain schedules when size-grading.Supplementing a dry, food diet with live zooplankton may become ofpractical interest for the typical freshwater cage fishfarmer in Norway.


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4 4 J. C . H o # n

Culturing l ive preyI n r e c e n t y e a r s , a lo t o f a t t e n t i o n h a s b e e n p a i d t o t h e e v o l u t i o n o f i n te -g r a t e d a q u a c u l t u r e s y s te m s o r c u l ti v a ti o n t e c h n i q u e s f o r c e r ta i n p r e ys pec i e s .S u r b e r ( 1 9 3 5 ) a c h i e v e d s o m e n o t a b l e r e s ul ts o n f e e d i n g B r o o k t ro u ta n d r a i n b o w t r o u t w i t h t h e f r e s h w a t e r a m p h i p o d G a m m a r u s fi~ sc ia tu s.H e s h o w e d t h a t 6 -0 5 k g ( w e t w e i g h t) w a s n e c e s s a D t o p r o d u c e 1 k g o fB r o o k t r o u t , w h i l e 6 " 6 3 k g o f a m p h i p o d s w e r e r e q u i r e d t o p r o d u c e t h es a m e a m o u n t o f r a i n b o w tr ou t. O n e k i lo g r a m o f a m p h i p o d s c o n t a i n e da n a v e r a g e o f a b o u t 5 8 0 0 0 i n d iv i d u a ls .I n t e n s i v e c u l t i v a t i n g o f t h e q u a n t i t y o f a m p h i p o d s r e q u i r e d f o r a f u l l -s c a l e a q u a c u l t u r e p l a n t ( e i t h e r p r o d u c i n g s m o l t or" f u ll y g r o w ns a l m o n i d s ) m u s t b e r e c o g n i z e d a s p r o b l e m a t i c i f n o t v e r y f a v o u r a b l ef a c il it ie s a n d r e s o u r c e s a r e p r e s e n t .I n t e n s iv e c u l ti v a ti o n o f c l a d o c e r a n s f o r g r o w t h f e e d i n g p u r p o s e sm u s t b e c o n s i d e r e d o f l o w e c o n o m i c i n te r e st . H o w e v e r , s u c h cu l ti v a-t i o n c a n b e o f a c e r t a i n i n t e r e s t in th e f ir s t f e e d i n g s i t u a t i o n , a t l e a s t f o rA t l a n t i c s a l m o n . P r o m i s i n g r e s u l t s , s h o w i n g h i g h g r o w t h r a t e w h e nu s in g li ve z o o p l a n k t o n a s a s t a r te r f o o d , a r e r e p o r t e d f r o m N o r w a y b yH o l m e t al . ( 1 9 8 2 ) a n d R e i n e r ts e n e t a l. ( 1 9 8 4 ) . C u l t iv a t in g t h e a m o u n to f D a p h n i a s p . n e e d e d f o r t h e f i r s t w e e k s s h o u l d b e t e c h n i c a l l yp o s s i b l e . S u c h c u l t i v a t i o n c a n o c c u r b o t h in s p e c i a l t a n k s u s i n g y e a s t o rm o r e e x t e n s i v e l y in e a r th p o n d s f o l lo w i n g t e c h n i q u e s a s u se d f o rc o m m o n c a r p ( C y p r i n u s c a r p i o ) r e p o r t e d b y K a f u k u a n d l k e n o u e( 1 9 8 3 ) A p r o b l e m is t h a t s u c h c u l t i v a t i o n m u s t o c c u r i n e a r l y s p r i n g i nh e a t e d w a t e r.

A n o t h e r a p p r o a c h is t h e u s e o f a c o n t r o l l e d e u t r o p h i c a t i o n i n n a tu r alw a t e r s y s t e m s . S u c h e u t r o p h i c a t i o n m a y , f o r e x a m p l e , b e t h e r e s u l t o fa g r i c u l tu r a l a c t M t y i n t h e d r a i n a g e a re a . A t l a n t i c s a l m o n sm o l t c a g ep r o d u c t i o n i n a e u t r o p h i c l a k e n e a r T r o n d h e i m h a s b e e n r e p o r t e d b yR e i n e r t s e n e t a l . ( 1 9 84 ) . B i o m a s s o f c l a d o c e r a n s in t h e u p p e r - 4 - m l a ye ro f t h e l a k e w a s a s h i g h a s 1 g D W m -3 i n J u n e , a n d t h e m a x i m u m v a l u e i nS e p t e m b e r w a s 0 -5 g D W m -~. T h e p r o d u c t i o n o f c l a d o c e r a n s w a s e st i-m a t e d to 3 0 - 6 0 ,, D W m -2 y e a r -~, m a k i n g 6 - 1 2 t o n n e s d r y w e i g h t f o rt h e w h o l e l a k e.

F i s h f a r m i n g a c t i v i t y w i l l i n d u c e e u t r o p h i c a t i o n i t s e l f . I n K v e r n a -v a t n e t , a to t a l a m o u n t o f 12 7 0 0 k g d r y f o o d p e l l e t s r e s u l t e d i n a n e s ti -m a t e d t ot al p h o s p h o r o u s i n p u t o f 2 3 0 k ~ in 1~ ' ' ',oo . O n l y 28 kgp h o s p h o r u s w e r e a c c u m u l a t e d in t h e f is h: t h e re s t m u s t b e r e c o g n i z e da s w a s te . E s t i m a t i n g t h e z o o p l a n k t o n p r o d u c t i o n a n d e v o l v i n g s u it a bl em a n a g e m e n t s t ra t e g ie s a r e t o p i c s fo r fu r t h e r w o r k .


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R e v i ew : . ~ o o p M n k t o n a s t b o d i t, s a l m o n M s m o l t p r o d u c t i o n 4 5Utilizing the live food simply by releasing the fish in the ecosystem hasseveral disadvantages. Controlling the predator pressure, both on foodand the salmonid, may be problematic. From Kvernavatnet it is shown

that the migration and subsequent trapping of the Atlantic salmon can beineffective due to wind and rain influence (Hansen et a l . , 1983~. Similarresults are reported from Scotland by Munro ( 1965'Collection of food organisms with different kinds of passive gearsare reported by different authors. Szlauer (1976) emphasizes the possi-bilities of using drift samplers in rivers draining lakes with dense zoo-plankton stocks. Mathias e t a l . (1982) used harvest nets set like gill netson the bottom in a Canadian lake to harvest the amphipod G a m m a r u sl a cu s t r i s . The amphipod appeared to be very suitable for rainbow troutculture. They were able to collect only adults with an average daily yieldof 61-92 kg with 0-9 x 257 m of 6.4 mm round-meshed netting.Pumps (Holm e t a l . , 1982; Holm, 1985b) and current setters (Holmand M~ller, 1984) for collecting planktonic crustaceans use probablymore energy per biomass unit than electric light bulbs as used by J~igerand Nellen (1980) or Szczerbowski and Mamcarz (1984), both rearingcoregonids. The last authors report that the abundance of zooplanktonnear the illuminated cages increased at night 1.4-fold in relation to thedaytime value, because organisms were attracted by the light.By manipulating the prey organisms behavior to achieve an attract-ing and concentrating effect before presenting it to the fish. the mostelegant and maybe cheapest methods could be developed.

ACKNOWLEDGEMENTSThe author would like to acknowledge the advice and cooperation ofDr Dag Moiler and his staff at the Institute of IVlarine Research, Deptof Aquaculture, in Bergen. The author is greatly indebted to DrGunnar Nazvdal of the Institute of Marine Research for inspiring dis-cussions and valuable comments on the manuscript. The research wasfinancially supported by the same institute, by the Norwegian FisheriesResearch Council and by BP Development Ltd, Norway.

REFERENCESAllen, D. J. ( 1981 ). Determinants of diet of Brook trout (Sa lve l in , t s fbn t ina l i s ) ina mountain stream. Uan..L F ish. Aq ua t . Sci . . 38, 184-92.Arnemo, R. (1975). Limnological studies in Hytt6dammen. 5. Outlines of theecosystem and its management, Swedish Sa lmot t Research Ins t i tu te Repor tLFI MEDD, August 1975.


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46 J. C. ftolmA rn e m o , R ., Pu k e , C . & S t e f fn e r , N .G . 1 9 8 0 ) Feed i n g d u r i n g t h e f i rs t w ee k s o fy o u n g s a l mo n in a p o n d . A rc . H v d r o b i o L 8 9 , 2 6 5 - 7 3.Ba ll, J. N . ( 1 9 61 ) . O n t h e fo o d o f t h e Br o w n t ro u t o f L l y n T eN d . Proc . Zoo l .S o c . Lo n d . , 1 3 7 , 5 9 9 - 6 2 2 .D ren ne r , R . W., S t r i ck le r , J . R . & O 'B r ien . W. J . ! 1978). C ap tur e p robab i l i ty : T hero l e o f zo o p l an k t o n e s cap e i n t h e s e l ec t i v e f eed i n g o f p l an k t i v o ro u s f i s h . , / ,Fish Res . Board Can . , 3 5 , 1 3 7 0 - 3 .H an s en , T . & H o l m , J . C . ( 1 98 1 ). S t a r t fd r i n g av r eg n b u e au re m ed d y re p l an k t o n(in ' " ~ . . . .o r~ eg lan , [S ta r t feed in~ o f ra in bow t rou t fr-v"w i t h zo o p l an k t o n ] . N o r s kF i s keo p p d r e t t , 1 2 . 6 - 7 .H an s en . T . , H o l m, J . C . , Mo l l e r , D . & T h o r s en , J . ( 1 9 8 2 ) . Set t e f i skoppdre t t ivassdrag ( i n N o r w e g i a n ) [ S m o l t Pro duc t ion in Natu ral Water Systems] , Fina lr e p o r t N F F R , P r o j e c t 1 7 0 1 .4 2 , N o r w e g i a n F i s h e r ie s R e s e a r c h C o u n c i l.H o l m, J . C . ( 1 9 8 5 a ) . L i v e an d f ro zen f r e s h w a t e r zo o p l an k t o n a s a l t e rn a t i v es t a r f f eed i n g d i e t s f o r A t l an t i c s a l mo n i n tr ay s , Coun . Meet . in t . Coun .

Exp lor . Sea 1985 , L o n d o n ( F : lS ) ( M i m e o g r . ) .H o l m , J. C . (1 9 8 5 b). U s e o f liv e f r e s h w a t e r zo o p l an k t o n fo r s t a r t f eed i n g A t l an ti cs a l mo n i n n e t p en s , Coun . Meet . in t . Coun . Exp lor . Sea 1985 . L o n d o n (F: 16 )(Mi meo g r . ) .H o l m. J. C . & M o i l e r . D . (1 9 8 4 ). G ro w t h an d p rey s e l ec t io n b y A t l an t ic s a l mo ny e a r li n g s r e a r e d o n l iv e f r e s h w a t e r z o o p l a n k t o n . A q u a c u l t u r e , 4 3 , 4 0 1 - 1 2 .H olm , J . C. , H anse n. , T. & M ~ller , D. ,' o ,q '~,~_ . , , . S t a r t f eed i n g o f s a l m o n i d s w i thl a k e z o o p l a n k t o n , Coun . Meet . in t . Coun . Exp lor . Sea 1982 , C o p e n h a g e n(F:36) (Mimeogr.) .I r v i n e . J . R . & N o r t h co t e , T . G . (1 9 8 3 ) . Se l ec t i o n b y y o u n g Ra i n b o w t ro u t(Sa lmo ga i rdner i ) in s i m u l a te d s t r e a m e n v i r o n m e n t s f o r liv e a nd d e a d p r e y o fd i f fe re n t s i zes. Can. J . Fish . Aquat . Sci . , 4 0 . 1 7 4 5 - 9 .Ivlev, V. S. ( 1961 ). E x p er i m en t a l E co l o g y o f th e F eed i n g o f th e F i s h es, Yale Uni-v e r s it y P re s s , N e w H a v en .J ~ig er , T . & N e l l en , W . (1 9 8 0) . D i e E rp r o b u n g e i n e r p o l n i s ch en M e t h o d e zu mVors t recken von Mar~inen in Sch leswig-Hols te in . Arbei t en e l . Deu t schenFischere iverbandes , 13, 14-31.K a f u k u , T . & I k e n o u e , H . (1 9 8 3) . M o d e r n m e t h o d s o f a q u a c u l t u r e in Ja p a n .D e ve l o p m en t s i n A q u a cu l t u r e a n d F i s h er ie s S c i en ces , 1 1 , 6 0 - 2 .Ly thgoe , J . N . 1966). V isua l p igmen ts an d u nd er w ate r v i s ion . In: Ligh t as anEcolog ica l Factor , ed s R . Ba i n b r i d g e , G . C . E v an s & O . R ack h am , B l ack w e l l,O x f o r d , p p . 3 7 5 - 9 I .M cCa r t , P . ( 1 9 6 7 ). B eh av i o u r an d eco l o g y o f So ck ey e s a l m o n f ry in t h e Bab i n eriver . J . F i sh . Res . Board Can . , 2 4 ~'~"~,. ,~7"g, ,+,o.~'~"M ath ias , J . A . , Ma r t in , J., Yurko wsk i , M. , Lark , J . G . I., Paps t , M. & T aba che k , J.g . (1982) . Harves t and nu t r i t iona l qua l i ty o f Garnrnarus lacustr is fo r t r o u tcu l tu re . Trans . Am. F i sh . Soc , 1 1 1, 8 3 - 9 .M orr i son . B. R. S . (1983') . Ob serv a t ion s on the fo od o f juven i l e At lan t i c sa lmon ,Sah no sa lar L . , rea red in a Sco t t i sh hil l l o ck J. Fish. Biol ., 2 3 , 3 0 5 - 1 3 .M ot t ram . J .C . "~ ' '9 , ,8a) T he feed ing o f t rou t f ry . I - - T he a lev in d i f f icu l ty . Fie ld ,581 .

M o t t ra m . J . C. ( 1 92 8 b ). T h e f e e d i n g o f t ro u t f r y. I I - E x p e r i m e n t s w i th t h ew ater f l ea . Fie ld , 6 5 4 - 5 .Mu n ro . W . R . (1 9 6 5 ) . T h e u s e o f h i l l l o ch s i n Sco t l an d a s r ea r i n g g ro u n d s fo ry o u n g s al m o n . P r o g re s s r e p o r t o n t h e e x p e r i m e n t in L o c h K i n a r d o c h y ! P e rt h -


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Rev iew: zoo plan kton as fo od in salrn onid sm oit pr~,duc[io;', -; 7shi rei , Coun . Meet . in t . Coun . Exp lor , Sea !965 , C o p e n h ag e n S a l m o n a n dT r o u t C o m m i t t e e N o . 5 8 ).M u rd o ch , W . G . B . ( 1 9 2 8 ). T h e f eed i n g o f t r o u t f ry . Fie ld . 721.Pau l . A . J, , Ho od , D . W. & N ev~, R. A . i 1976). A no te on rear ing juven i l e ch ums a l mo n , O n c o r h y n c h u s k er n. i n an a r t if i c ia l upw el l ing sys tem. A qua cu l ture , 9 ._ , ~ / - 9 0 .Pep per , V. A., Nich ol ls , T. & Ol iv er , N . P. i 19~31~. A t lant ic salm on f~" rea r ing19b_. Court . 3leer. int . Coun. Exptor.xp er im ent s in Ne~ vfound tand dur in ,,~ ' "Sea 1983 . G o t h en b u rg (F : 1 4 ) (Mi m eo g r . ) .Re iner t sen , H . , Au naa s . T ., Gjov ik , J. A . , Jense n , A . . N~ess B. & O tsen , Y .,r 1984). Forsook re ed oppf6rin , ,= av laksevn~el , re ed dvrep lankton , som f6r-g runn lag ( in Nor~veg ian) [S ta r t feed ing o f At lan t i c sa lmon wi th zoop lank ton] .No r s k F i s keo p p d r e t t . 5 / 8 4 . 2 8 - 3 1 .R i m m er , D . M. & Po w er , G . (19 7 8 ) . Feed i n g r e s p o n s e o f A t l an t ic s a l mo n ( S a l m osalar) alevins in f lowing an d s ti ll water . J. Fish . Res . Board Can. , 3 5 . 3 2 9 - 3 2 .

Su rb e r , E . W . (1 9 3 5 ). T ro u t f eed i n g ex p e r i me n t s w i th n a t u ra l f o o d ( G a m m a r u sfi~sciatus). A m . Fish. Soc. , 6 5 , 3 0 0 - 4 .S z c z e r b o w s k i, J. A . & M a m c a r z , A . ( 1 9 8 4 . R e a r i n g o f c o r e g o n i d f is h es(C o re ~o n i d ae i n i l lu m i n a t ed l ak e ca , ,e s [I. E n v i ro n me n t a l co n d i t i o n s d u r i n ofish rear ing . A q u a c u l t u r e . 4 0 , 1 4 7 - 6 1 .Sz lauer , B . (1976) . Poss ib i l i t i es o f us ing zoop lank ton removed by the r iverP l o n i a f ro m l ak es t o f eed y o u n g f i s h . Acta [chthyotogica et Piscatoria , 6 ,,,9-_~3.U rq u h a r t , D . L . & B arn a rd . D . R . ( 1 9 7 9 ) G ro ~v th o f p en r ea r ed p i n k s a l mo n f ry(O t t co r h yn ch u s g o r b u s ch a ) , f eed i n g o n av a i lab l e mar i n e zo o p l an k t o n . A q u a -cul ture, 1 7, 2 5 1 - 6 .

holm 1986 aquacultural-engineering

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