holm 1987 aquacultural-engineering

7/28/2019 Holm 1987 Aquacultural-Engineering

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Aqu acultural Engineering 6 ( 1987) 1-14

A t l a n ti c S a l m o n S t a r t- F e e d in g w i th L i v e Z o o p l a n k t o n :P r e s s u r e S h o c k T r e a t m e n t to I n c r e a s e P r e y A v a ila b il ity

Jens Chr. H olmDepartment of Fisheries Biology,Universityof Bergen,PO Box 1839,N-5011 Nordnes,Norway

A B S T R A C TThe ex per im en t w as carried o ut in 1 98 4 in a coastal lake near Bergen,Norway. A total o f fou r ( later eight) groups o f At lan t ic salm on (Salmosalar) fry were start-fed w ith live zoo pla nkto n delivered by a pu m p. Sm allf ine-m esh ed ne t pen s were used . Supplementa l feed prom oted addi tionalgrowth after the start-feeding ph ase.The fish in zoo pla nk ton -fed groups increased th eir average length b yO"15 m m /da y during the f irs t 30 days com pared with 0"08 turn/day in f ishgiven bo th zo opla nkto n an d dry feed. Ini t ial fo od lack ( low density o fcladocerans) is the m ain explanation fo r the lo w growth rates. Fo od selec-t ion a nd pum p-incr ease d zo oplan kton capture probabil it ies are alsodiscussed. A n unex pected avoidance o f calanoid copepods, even wh endebil itated, was observed at the end o f the experim ent w hen o ther poten -tial prey species were scarc e. E ve n Daphnia were not preferred asexpected. Live zo opla nkton is rec om m en de d fo r init ial start- feeding, b utdry foo d sho uM be avai lable to sa lmon when the yo lksac has beenabsorbed.

INTRODUCTIONMost fish feed on plankton prey during some period of their lives. Thecrustacean zooplankton plays an important role, specially for theyoungest stages. Young stages of the genera S a l m o and O n c o r h y n c h u shave been successfully reared on live zooplankton for shorter periods(Paul et al. . 1976; Fast, 1978; Urquhart and Barnard, 1979; Holm andMoiler, 1984; Holm, 1986).Preliminary experiments on first feeding in net pens of Atlanticsalmon ( S a h n o s a l a r ) and rainbow trout (S. gairdneri) with live z o o p l a n k -

1Aqzmcult , ral Engi ,eo4ng 0144-8609/87/S03.50-- Elsevier Applied SciencePublishers Ltd. England. 1987. Printed in Great Britain


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2 J . C . H o l mt o n g a v e s u r p r is i n g ly h i g h g r o w t h r a t e s u p t o a c e rt a i n p e r i o d , a f t e r w h i c ht h e g r o w t h r a t e d e c r e a s e d ( H o l m e t a l . , 1 9 8 2 ) . A t l a n t i c s a l m o n f r yr e a r i n g w i t h l i v e z o o p l a n k t o n i n c u l t u r e i s a l s o r e p o r t e d b y P e p p e r e t a l .( 1 9 8 3 ) a n d R e i n e r t s e n e t a l . ( 1 9 8 4 ) . S e m i n a t u r a l f ir s t f e e d i n g i n p o n d s isr e p o r t e d b y A r n e m o e t a l . ( 1 9 8 2 ) a n d n a t u r a l f e e d in g o n z o o p l a n k t o n ina ri v e r is d e s c r i b e d b y L i l l e h a m m e r ( 1 9 7 3 ) .F o o d s e l e c t i o n o n s p e c i e s a n d s i z e l e v e l o c c u r s i n g e n e r a l . D i f f e r e n tm e c h a n i s m s a r e i n v o l v e d ; o n e i s p r e y f l i g h t s u c c e s s . M i l i n s k i a n dL 6 w e n s t e i n ( 1 9 8 0 ) t e s t e d t h e h y p o t h e s i s t h a t t h r e e - s p i n e d s t i c k l e b a c k s( G a s t e r o s t e u s a c u l e a t u s ) s h o u l d p r e f e r d e b i l i t a t e d w a t e r f l e a s . T h e y d i dn o t s h o w s u c h p r e f e r e n c e , p r o b a b l y d u e t o t h e f a c t t h a t t h r e e - s p i n e ds t i c k l e b a c k s a l m o s t n e v e r m i s s a p u r s u e d ( h e a l t h y ) w a t e r f l e a . H o l m( 1 9 8 5 ) r e p o r t s n e g a t iv e e l e c ti v it y f o r s o m e o f t h e o f f e r e d z o o p l a n k t o ns p e c i e s w h e n s t a r t - f e e d i n g A t l a n t i c s a l m o n . T h i s i s p r o b a b l y p a r t l y d u et o h ig h e v a s i v e s u c c e ss , e sp e c i a ll y o f t h e c o p e p o d s . H o l m f o u n d t h a tn o r m a l l y f r o z e n z o o p l a n k t o n g a v e u n s a ti s fa c t o r y g r o w t h r a t es . T h i s c a nb e r e l a t e d t o l o w n u t r i ti o n a l v a l u e a n d / o r s u b o p t i m a l f e e d i n g in t en s it y . I fd e c r e a s e d f l i g h t s u c c e s s i n c o p e p o d s c a n b e a c h i e v e d , b e t t e r f e e d i n gc o n d i t i o n s f o r t h e s a l m o n s h o u l d b e s u g g e s t e d a s a r e su l t, w h e n o f f e ri n gn a t u r a l z o o p l a n k t o n .

T h e e x p e r i m e n t r e p o r t e d h e r e e v a l u a te s th e u s e o f a p u m p s y s te m tos h o c k t h e p l a n k t o n , t h u s r e d u c i n g t h e i r e v a s i o n e f fi ci en c y . T h e a i m o f th ed e s i g n w a s t o o f f e r th e f is h s lo w l y e v a d i n g o r f r e s h l y k il le d z o o p l a n k t o n .

M A T E R I A L S A N D M E T H O D SExp erimental conditionsA t o ta l o f 2 4 0 0 0 A t l a n ti c s a l m o n f r y f r o m M a t r e A q u a c u l t u r e S t a ti o n( D e p t o f A q u a c u l tu r e , I n s ti tu t e o f M a r i n e R e s e a r c h , D i r e c t o r a t e o fF i s h e r i e s) w e r e t r a n s p o r t e d 3 M a y 1 9 8 4 ( D a y 0 ) t o t h e c o a st a l l a k eK v e m a v a t n e t ( C o m m u n i t y o f A u s t e v o ll , s o u t h -w e s t o f B e r g e n , N o r w a y ) .T h e f ry w e r e h e l d 2 0 0 d a y d e g r e es p o s t - h a tc h i n g b e f o r e t ra n s p o r t . T h ef ry w e r e d i v id e d i nt o f o u r n e t p e n s, p r o v i d in g 6 0 0 0 f r y /g r o u p . A t D a y 0 ,3 7 % o f t h e t o t a l d r y w e i g h t c o n s i s t e d o f y o l k ; a t d a y 1 1 , 2 0 - 2 3 % w a sy o l k .A s p e c i a l p e n u n i t w a s c o n s t r u c t e d f o r th e e x p e r i m e n t . I t c o n s i s te d o fa m a x i m u m o f ei gh t p e n s ( o n ly f o u r o f w h i c h w e r e u s e d f r o m t h e s ta r t o ft h is e x p e r i m e n t ) , e a c h w i t h a v o l u m e o f 2 m 3. A 5 - m m ( s tr e t c h e d m e s h )n e t w a s u s e d i n t h e p e n s ; i n n e r p e n s o f 1 m m x 1 m m - m e s h p l a n k t o n n e t


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Atlantic salm on start- feeding with l ive zoop lank ton 3

. . . . . . . D

F i g . 1 . E x p e r i m e n t a l p e n s . A r r o w s i n d i c a te w a t e r i nl et .

w er e u sed in t h e f i r s t t h r ee w eek s , en su r in g n o e scap e . A sk e t ch o f t h eex p e r im en ta l p en s i s sh o w n in F ig. 1 .W a t e r w a s d e l i v e r e d b y a je t p u m p w i th a c a p a c i t y o f 1 5 0 0 l it r e /m i n .H i g h p r e s s u r e f o r s h o c k i n g z o o p l a n k t o n w a s o b t a i n e d i n t h e p i p e l in e

sy s t em s imp ly b y ad ju s t i n g e s sen t i a l v a lv es t o a lmo s t c lo sed p o s i t i o n s .W a t e r s u p p l y t o e a c h p e n u n i t c o u ld b e a d j u s te d s e p a ra t el y . I n l e t c u r r e n tv e lo c i ti e s w er e ad ju s t ed t o eq u a l va lu es. W ate r w as t ak en 2 m b e lo w th esur face .I n t h e f i r s t p e r io d ( 5 May - 4 Ju n e ) , a l l f o u r g r o u p s w er e o f f e r edn a t u r a l l y o c c u r r i n g z o o p l a n k t o n th r o u g h t h e p u m p - d e l i v e r e d w a te r. O n eo f t h e g r o u p s w as o f f e r ed d r y f o o d ( E w o s ty p e 1 ) i n ad .d it io n . O n 4 Ju n e(Day 32) , a l l the g ro up s w ere sp l i t , m akin g a to ta l o f e igh t g roups . In th el a st p e r i o d (4 J u n e - 1 8 J ul y) , f o u r g r o u p s w e r e o f f e r e d li ve z o o p l a n k t o no n ly , a n d f o u r g r o u p s w e r e o f f e r e d b o t h l iv e z o o p l a n k t o n a n d d r y f o o d .T w o o f t h e se w e r e f e d b o t h f o o d t y p e s t h r o u g h t h e w h o l e e x p e r i m e n t a lp e r i o d ; tw o w e r e s w i t c h e d f r o m li ve z o o p l a n k t o n t o b o t h f o o d t y p es a tD a y 3 2 .T h e w a t e r t e m p e r a t u r e v a r i e d b e tw e e n 1 5 a n d 2 0 C i n t h e e x p er i-m e n t a l p e r io d .


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4 J . C H o l m

S a m p l in g a n d m e a s u r e m e n t sZ o o p l a n k t o n e n t e r i n g t h e c a g e s t h r o u g h t h e p u m p a n d p i p e l i n e s w e r es a m p l e d a l m o s t e v e r y w e e k ( e xc e p t f o r 1 2 J u n e - 1 7 J u ly ) w i t h a0 . 04 5 m m p l a n k t o n n e t f o r a t l e as t 5 m i n . L e n g t h m e a s u r e m e n t s o f th ec l a d o c e r a n Bosmina long isp ina we r e t a k e n f r o m t h e t o p o f t h e c r e s t t othe base o f t he she l l - sp ine .Sa m p l e s f o r e s t i m a t i n g th e z o o p l a n k t o n su r v i v a l r a t e a f te r p a s s in g t hep u m p a n d p i p e l i n e s w e r e o b t a i n e d w i t h t h e s a m e n e t . T h e z o o p l a n k t o nwe r e t r a n s f e r r e d t o a c y l i n d e r a n d k e p t i n t h e d a r k f o r 1 0 m i n . A sm a l lf r a c t i o n ( 4 % o f t h e t o t a l v o l u m e ) f r o m t h e b o t t o m w a s s u p p o s e d t oc o n t a i n d e a d a n i m a l s ; t h e r e s t c o n t a i n e d l i v e ( h e a l t h y o r d e b i l i t a t e d )an ima l s .A m i n i m u m o f 9 0 f i sh we r e s a m p l e d a t t h e s a m e t i m e as th e z o o -p l a n k t o n s a m p l i n g f r o m e a c h n e t p e n . B o t h z o o p l a n k t o n a n d f i s h w e r ep r e s e r v e d i n s t a n d a r d n e u t r a l 4 % f o r m a l d e h y d e s o l u t i o n . F o r k l e n g t h swe r e m e a su r e d o n p r e se r v e d m a t e r i a l . F r o m e a c h s a m p l e , 4 8 i n d i v i d u a l swe r e d i s se c t e d a n d we i g h e d a f t e r f r e e z e - d r y i n g t o t h e n e a r e s t m i l l i g r a mo n a n e l e c t r o n i c m i c r o b a l a n c e . M e a n t o t a l we i g h t, y o l k we i g h t a n d t o r sowe i g h t ( b o d y we i g h t ) we r e c a l c u l a t e d . T h e m e a n y o l k a b so r p t i o n r a t e( Y A R )

Y A R = Yo l k we i g h t a t ti m e 2 - - y o l k we i g h t a t ti m e it ime 2 - - t ime 1 (days)was a l so ca l cu la t ed : Yolk was p resen t i n a l l f i shes in samples t aken inM a y ( b e y o n d D a y 2 6 ) . F r o m e a c h f i s h s a m p l e , t h e s t o m a c h c o n t e n t sf r o m a t l e a st te n f i sh we r e e x a m i n e d .

R E S U L T SO f f er e d an d c o n s u m e d z o o p l a n k t o nT a b l e 1 p r e s e n t s t h e z o o p l a n k t o n c o m p o s i t i o n e n t e r i n g t h e n e t p e n st h r o u g h t h e p u m p . T h e r e l a t i v e a b u n d a n c e o f Bosmina longispinai n c r e a se s f r o m D a y 1 1 t o D a y 4 0 . Daphnia longispina a re sca rce ; h ighes tv a l u e s we r e o b t a i n e d a t t h e e n d o f t h e e x p e r i m e n t .T h e p u m p p r o d u c e d a h i g h p r e s s u r e i n t he p i p e li n e s y s t em f r o m t h ep u m p t o t h e v a lv e s su p p l y i n g e a c h n e t p e n . A n i n d i c a t i o n o f sp e c ie s -spec i f i c su rv iva l o f t he p ressure - shock i s i nc luded in Tab le 1 . B o s m i n asu r v i v e d t h e t r e a t m e n t r e la t iv e l y we l l, m o r t a l i ty v a r y i n g f r o m 2 0 t o 3 0 % .


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Atlantic salmo n start-feeding w ith live zoop lanktonT A B L E 1Com pos it ion of Pum ped Zo oplankton E ntering the Net Pens .

Group Com position (%)~Day 11 Day 19 Day 26 Day 33 Day 40 Day 75

Bosmina 2'5 (80.1) 2'9 8.6 (70"5) 12 '1 49.3 (72.0)Daphnia 0"1 (4 3. 8) 0"2 0"2 (45 -5) 5"0 6.7 (30"4)O the r clad- 0 0"1 0 0 0.7 (--)oceransC alano id 77 . 8 ( 2 7 . 6 ) 70.4 5 9 . 8 ( 3 5 . 4 ) 4 8 - 6 24.0 ( 38 .1 )copepodsC yclo po id 1 9 . 6 ( 1 6 . 1 ) 26.4 3 1 . 4 ( 5 . 9 ) 3 4 . 3 1 9 . 3 ( 4 .0 )copepods

Nu m be r in 2 831 4 586 12 994sample, N

0"6 (78"0)20"0 (10"5)29"0 (--)49"8 (25"6)

0"6 (7"1)1 550

"Percentage survival 10-15 min after pump passage through the pump is shown inparentheses.

T A B L E 2Bosmina/Daphnia Ratios in Free W ater Masses and in Pu m ped W aterDay 19 Day 26 Day 23 Day 33 Day 75

Fre e w ate r m asses" 0.7 1.2 0.3 0.2 0.1Pu m pe d w ater 14.5 43.0 2.4 7.4 < 0.1"Data from free water masses are m ean values from 1 and 3 m de pths of three s tat ionsfrom Johnse n iunpublished work).

S u r v i v a l o f D a p h n i a a n d c a l a n o i d c o p e p o d s w a s j u d g e d a s fa i r ly si m il ar ,w h i le c y c l o p o i d c o p e p o d s s h o w e d h i gh e s t m o r t a l i ty w h e n p a ss in gt h r o u g h t h e p u m p / p i p e l i n e s y st em .

I n o r d e r to e v a l u a t e b ia s b e t w e e n n a t u ra l ly o c c u r r i n g z o o p l a n k t o n inf r e e w a t e r m a s s e s a n d z o o p l a n k t o n e n t e r i n g th e p u m p in le t , t h e r a t i o o fB o s m i n a t o D a p h n i a o c c u r r e n c e w a s c a l c u l a te d . T h e r e su l ts a r e g i v e n inT a b l e 2 ; t h e y s h o w a h i g h e r o c c u r r e n c e o f B o s m i n a i n t h e p u m p s y s t e mc o m p a r e d w i th t h a t in f r e e w a t e r m a s s e s .

F r o m t h e t w o o r i g i na l z o o p l a n k t o n - f e d g r o up s , z o o p l a n k t o n c o n -s u m p t i o n in s a l m o n is o b t a i n e d f r o m t w o s a m p l e s f o r e a c h s a m p l i n gd a te . C o p e p o d s w e r e t h e m a i n p r e y u n ti l t h e e n d o f M a y , w h e n B o s m i n a


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6 J. C Holmbecame most important. As long as copepods were the most abundantfood source, half of the salmon had empty stomachs. In the sample ofDay 26, all fish had stomach contents (mainly Bosmina), and at this datethe highest mean number of prey in the stomach occurred. Later, theprey number decreased and the relative number of empty stomachsincreased. Zooplankton consumption is given in Table 3.In Table 4 the composition of the prey in the groups fed both dry foodand live zooplankton over the whole experimental period is presented.Fish with both food types in the stomach contents (B) are distinguishedfrom individuals with only zooplankton present in the stomach (Z).Species selection seems not to be affected by dry food occurrence in thestomach. The same Table shows percentages of empty stomachs ingroups fed both food types. From 14 May (Day 11), when no food waspresent, the relative number of empty stomachs decreases. The numberof zooplankton in stomachs increases throughout the experimentalperiod. The relative number of fish with both food categories present(type B) varied from 46 to 72%.

In Table 5, Bosmina lengths in both the offer and the stomachcontents from zooplankton-fed groups are presented. Significant sizeselection was obtained on Days 26 and 75, but not on Day 40.Table 6 presents the mean number of zooplankton found in stomachsfrom fish fed both food categories, on Day 40. Numbers of zooplanktonwere significantly higher in the zooplankton-fed group in fish larger than30 ram, compared with the combination-fed group. Dry food waspresent in the combination-fed group for fishes larger than 26 ram.

T A B L E 3P r e y G r o u p C o m p o s i t i o n , M e a n P r e y N u m b e r p e r F i s h a n d P e r c e n t a g e o f E m p t yS t o m a c h s in Z o o p l a n k t o n - F e d A t la n ti c S a l m o n G r o u p s

Group Mean composition (%)Day 11 Day 19 Day 26 Day 40 Day 75

Bosmina 3'8 7"4 59.2 51.5 93.0Daphnia 3-8 7"4 1.2 4.6 7.0Ca lano id co pe po ds 11 .5 33-3 19 .8 18. I 0Cy c lop oid co pe po ds 80"9 51 "9 19 .8 25 .8 0E m p t y s t o m a c h s (% ) 4 8 4 8 0 1 9 2 0M e a n p r e y nu m be r / 5 "2 8 ' 0 9 ' 3 8 "3 6" 1fishN u m b e r o f f is h e x a m i n e d , N 2 1 2 3 3 0 2 7 4 9


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A t l an t i c s a l m on s ta r t- fe e d ing w i t h l iv e z oop l a nk t on 7

T A B L E 4P r e y G r o u p C o m p o s i t i o n i n G r o u p s F e d B o t h Z o o p l a n k t o n a n d D r y F o o d D u r i n g t h eW h o l e E x p e r i m e n t a l P er io dG r o u p ~ C o m p o s i t io n ( % b

D a y 11 D ay 19 D a y 26 D a y 40 D a y 75B o s m i n a B - - 15 .1 52 .1 21 .9 86 .7

Z - - 28 .6 21 .6 21 .6 92"2D ap hn i a B - - 0 0 0 0Z - - 0 0 0 0Ca l a n o i d c o pe po ds B - - 36 . 2 20" 8 37 . 2 6 "6

Z - - 23 .8 25 .5 47 .3 3-5C y c l o p o i d c o p e p o d s B - - 4 8 . 7 2 7 .1 4 0 -9 6 .7Z - - 47 .6 52 .9 30 .1 4"3

E m pt y s t om a c hs ( %) 100 29 . 8 27" 8 12" 5 5 ' 5M e a n n u m b e r o f 0 8 .0 5 -6 1 2 .4 3 7 .4z o o p l a n k t o n / f i s h t y p e BM e a n nu m be r o f 0 3 .8 5 .1 14- 8 66 - 3

z o o p l a n k t o n / f i s h t y p e ZN u m b e r o f f is h e x a m i n e d , N 1 8 5 7 3 6 5 6 1 8

B, ba s e d on f i s h w i t h bo t h f ood c a t e go r i e s i n t he s t om a c h ; Z , ba s e d on f i s h w i t h on l yz o o p l a n k t o n p r e s e n t in th e s t o m a c h .bE x c e p t f o r e m p t y s t o m a c h o c c u r r e n c e , a l l v a l u e s ar e b a s e d o n f i sh w i th f o o d p r e s e n t i nt he s t om a c h .

T A B L E 5M e a n B o s m i n a L e n g t h s ( r a m ) f r o m O f f e r( I n l e t ) a n d S t o m a c h C o n t e n t s f o r P e n s 5 - 8( G r o u p s F e d Z o o p l a n k t o n )

D at e M e an l eng th ( m m ) "I n l e t S t om ac h

D ay 26 0 .43 + 0 .03 0"55 + 0"03D ay 40 0-51 _ 0"03 0"50 _+ 0"03D a y 7 5 0 . 4 9 + 0 . 0 4 0 .6 1 _ +0 .0 4" C on f i de n c e l im i t s ( 95%) a r e i nd i c a te d .


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8 J . C . H o l mT A B L E 6P r e d a t o r - S i z e S e l e c t i v e F e e d i n g o n D a y 4 0 B a s e d o n L a r g e S a m p l e s o f F i s h N o t

I nc lude d in Ta b le 4Fish s i ze group(mm) M e a n n u m b e r o f z o o p l a n k t o n p r e se n t in s t om a c h a

Z o o p l a n k t o n - f e d g r o up Com bi na t i on - f e d g roup< 2 4 " 0 1 0 + 7 ( 6) 1 0_ +8 (7 )24" 0-2 5"9 8_+6 (11) 15_+9 (9)26"0-2 7"9 12_+11 (21) 13_+5 (23)28" 0-29 "9 20_+ 11 (20) 10_+6 (30)

3 0 - 0 -3 1 " 9 2 8 _ + 1 5 ( 12 ) 7 + 4 ( 22 )>3 2" 0 35_+10 ( 12 ) 0 ( 15 )a T he 95% c on f ide nc e in t e r va ls a r e i nd ic a t e d . S a m ple s i z e is g ive n in pa r e n the se s .

G r o w t h r a t e a n d s u r v iv a l in s a l m o nI n t h e f i rs t 3 0 d a y s o f th e e x p e r i m e n t , z o o p l a n k t o n - f e d g r o u p s i n c r e a s e dt h e i r l e n g t h a t a n a v e r a g e o f 0 . 1 5 m m / d a y . F i s h w h i c h r e c e i v e d b o t hz o o p l a n k t o n a n d d r y f o o d o b t a i n e d a g r ow t h r a te o f 0 .0 8 m m / d a y . M e a nd r y w e i g h ts a r e g i v e n i n F ig . 2 . Z o o p l a n k t o n - f e d g r o u p s s h o w e d t h eh ig h es t g r o w th r a t e u n t i l D ay 3 2 , an d w er e s ig n if i can tly l a r g e r o n D a y 3 2th an d r y - f ed g r o u p s ( P < 0 -0 5 , S tu d en t ' s t- te s t) . A t t h e t e r m in a t io n o f th ee x p e r i m e n t g r o u p s f e d w i th a c o m b i n e d d i e t w e r e s ig n if ic a n tl y h e a v i e rth an zo o p la n k to n - f ed g r o u p s ( P < 0 "0 5, S tu d en t ' s t - te st ).A t t h e en d o f th e ex p e r im en t t h e f ish w er e co u n ted ; su r v iv a l v a lu es a r eg iv en in T ab le 7 . Su r v iv a l r a t e s w er e h ig h es t i n g r o u p s f ed d r y f o o dd u r i n g t h e w h o l e e x p e r i m e n t a l p e r i o d . S e c o n d c a m e g r o u p s g i v e n d r y .f o o d i n a d d i t io n to z o o p l a n k t o n f r o m D a y 3 2.I n F ig . 3 , t o r so g r o w th r a t e s a r e p r esen t ed .

D I S C U S S I O NF o o d p r e f e r e n c e a s a f u n c t i o n o f t o ta l fo o d d e n s i t y a n d f is h s i z eW h e n o f f e re d b o t h f o o d t yp e s o n D a y 4 0 , t he s a l m o n s e e m e d t o p r e f erd i f f e re n t o n e s d e p e n d i n g o n i ts o w n s iz e. T h i s o c c u r r e d w h e n Bosminaw as th e m a in p r e y i t em a n d n o s ig n if i can t s ize s e lec t i o n w as o b se r v ed inz o o p l a n k t o n - f e d g ro u p s . A c c o r d i n g t o H o l m a n d M o i l e r ( 1 9 84 ) , th is c a nb e t a k e n a s a n i n d i c a t o r o f la c k o f f o o d , a n d o b s e r v e d s iz e s e le c t i o n o n


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F ig . 2 . M e a n d r y we igh t s o f A t l a n t i c sa lmon . P e ns 5 - 8 r e c e ive d l ive z oop la nk ton ; a ndpe ns 1 a nd 2 r e c e ive d bo th f ood type s du r ing the who le pe r iod ; pe ns 3 a nd 4 r e c e ive dl ive z oo p la n k ton un t il Da y 32 , a nd l a t e r bo th f oo d c a t e go ri e s .

T A B L E 7S ur v iva l i n Ne t P e ns, 3 M a y - 1 8 Ju ly (Da y 76 )Pen Die t Surv iva l (%)0

1 C o m b i n a t i o n 7 1 "5 82 C o m b i n a t i o n 7 4 . 0 73 Z o o p l a n k t o n - c o m b i n a t i o n 5 5" 634 Z o o p l a n k t o n - c o m b i n a t i o n 5 6 '3 15 Z o o p l a n k t o n 3 5 .0 36 Z o o p l a n k t o n 3 9 .6 37 Z o o p l a n k t o n 4 9 . 948 Z o o p l a n k t o n 4 7 . 0 4

" S a m ple d f i sh a r e sub t r a c t e d f r om in itia l n um be r b e f o r e theca lcu la t ion .


10/14

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descr ibed in the l egend to F ig . 2 .D a y 7 5 c o u l d b e g il l- r ak e r - d e p e n d e n t . T h e s m a l le s t Bosmina i nd iv idua l s( b e l o w 0 . 4 m m i n l e n g t h ) h a v e t h e a b i l i t y t o e s c a p e b e t w e e n t h e s a l m o ng i l l r a k e r s . A c c o r d i n g t o V i s s e r ( 1 9 8 2 ) , ( i ) p r e f e r e n c e f o r t h e m o r ep o p u l a r p r e y i n c r e a s e s w h e n t h e t o t a l p r e y d e n s i t y i n c r e a s e s , a n d ( i i )p r e f e r e n c e f o r t h e r e l a t i v e l y s c a r c e p r e y i n c r e a s e s w h e n t h e t o t a l p r e yd e n s i t y i n c r e a s e s .

W h e n o f f e r i n g t h e s a l m o n b o t h l i v e z o o p l a n k t o n a n d d r y f o o d , t h et o ta l p r e y d e n s i t y is h i g h e r t h a n i n th e z o o p l a n k t o n - f e d g r o u p s . D r y f o o dm u s t b e e x p e c t e d t o b e m o s t p o p u l a r d u e t o (1 ) l a r g e r f is h i n c o m p e t i t io nw i t h s m a l l e r f i s h s h o w p o s i t i v e e l e c t i v i t y f o r d r y f o o d , a n d ( 2 ) z o o -p l a n k t o n - f e d f i s h s e l e c t Bosmina a n d Daphnia a t higher r a t e s t h a n f i s hf e d b o t h f o o d t y p e s . I f o n e o f t h e c l a d o c e r a n s p e c ie s w e r e m o s t p o p u l a r ,s t r o n g e s t s e l e c t i o n s h o u l d o c c u r i n g r o u p s f e d b o t h f o o d t y p e s ( h i g h e rt o t a l p r e y d e n s i t i e s ) . Z o o p l a n k t o n , i n c l u d i n g c l a d o c e r a n s , s h o u l d t h e r e -f o r e b e c la s s if ie d a s s u b o p t i m a l c o m p a r e d w i t h d r y f o o d .P u m p - i n c r e a s e d c a p t u r e p r o b a b i l i t i e sC o p e p o d s w e r e t a k e n o n D a y 4 0 i n s u c h h i g h n u m b e r s b y t h e s a l m o nt h a t n e g a t iv e e le c ti v it y c a n n o t b e a s s u m e d . A h ig h r a t e o f f e e d i n g o nc o p e p o d s o c c u r r e d s i m u l t an e o u s ly w ith c l a d o c e r a n d e p le ti o n . C o p e p o d s


11/14

A t l an t i c s a l m on s t a rt -f e e d ing w i t h l iv e z oo p l an k t on 11were negat ively se lec ted again on Day 75 . This i s hard to expla inbecause o f t he observed empty s tomachs (20%) in zoop lank ton- fedgroups . Cyclopoid copepods seemed to be s l ight ly more popular thancalanoid ; they have shor ter an tennae and showed the h ighes t mor ta l i tyra t e when pass ing the pum p sys tem.Scheib l ing (1984) showed that rock c rabs (Cancer i rrora tus) pre fe r reddiseased or narcot ized sea urchins (Strongylocentrotus droebachiensis)over hea l thy ones and fed upon them a t much h igher ra t es t han c rabsgiven only heal thy sea urch ins as prey. Scheibling suggested that heal thysea urchins may aggregate and avoid predat ion . Therefore , fac torsinf luencing predator success o ther than prey movement i t se l f can be ofimpor tance a l so when prey i s debi l i t a ted or morbid . Copepods wi l lno rmal ly evade cap tu re w hen a t t acked by A tl an ti c s a lmo n under n orma lcond i t i ons (Arnemo e t aL , 1982; Holm and Moi ler , 1984; Holm, 1985) .Zo op lank ton f light success and abi li ty to patch can be inf luenced by h ighcurren t velocity (Holm et al. , 1982) o r b y p res su re shock .A t t he end o f exper imen t a lmos t no cyc lopo id copepods were be ingoffered to the salmo n, so i f foo d spe cial izat ion is es tabl ished lack ofcalanoid cop epo ds in the s tomac h can par t ly be explained . Th e ob servednegat ive e lect iv i ty for ca lanoid c ope pod s should no t be exp ected , due tothei r pump-induced debi l i t a t ion . D a p h n i a did not show up to be themajo r food i t em, bu t was more popu la r i n t he zoop lank ton- fed g roup .Holm and Moi l e r (1984) repor t ed D a p h n i a special izat ion in salmonyear l ings which d id not occur in the present exper iment . Iv lev (1961)and Dil l (1983) showed that learning can resul t in t raining biases andfood specia l iza t ion . T he low survival ra te , com bined wi th the occurren ceof em pty s tomach s , indicates subop t im al condi t ions for the zoop lankton-fed salmo n.Feeding and growth rateDe pen ding on f i sh s ize, sa lmon se lec ted d i f ferent food types on D ay 40 .Mil inski (1982), feeding three-spined s t icklebacks with D a p h n i a ,showed that more successfu l compet i tors concent ra ted on large prey ,whereas the poorer compet i tors fed as general is ts but not unselect ively.H o l m et al. (1985) repor ted a bet ter growth ra te in At lant ic sa lmon fedon a two-colour d ie t compared wi th a normal one-colour d ie t . Theysuggested that the sm al ler f ish hav e to pa y mo re a t tent ion to conspecif icsthan large ones, and thus tolerate less confusion when feeding. Thus,lower ing the cos t of confus ion w i ll pro m ote a h igher to ta l growth ra te .Therefore o ther explanat ions have to be found for the re la t ively lowgrowth ra te (Days 0-30) found in groups offered both food types . A


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12 J . C . H o l mposs ib le explanat ion is that l ive zooplankton may cons is t of impor tantnutr i t ional com pon ents ( free am ino acids , enzymes), wh ich are d i f f icul tto keep in comm ercia l dry food (H olm and M oiler , 1984; Holm , 1985).Food availabil i tym ay a lso be h igher in zooplank ton-fed groups .Later, groups fed bo th types showed high growth ra tes. T his could beexpla ined by lowered in t raspeci f ic compet i t ion in combinat ion-fedgroups in addi t ion to food lack in zooplankton-fed groups where there la t ive nu m bers of emp ty s tomachs inc reased la te in the exper iment .Concluding remarksTable 8 c om pares som e results from s tart - feeding exper iments . H an senand T orr issen (1984) o bserved negat ive or no weight increm ents dur ingthe f i r st 32 days o f feeding in large-scale dry-food rear ing of At lant icsa lmon. T he phys io logical ages of these f ry were qui te com parab le wi ththe groups out l ined in Table 8 , but the mean water temperature waslower.

T A B L E 8C o m p a r i s o n s o f G r o w t h R a t e s o f A t la n ti c S a l m o n D u r in g t h e F i r st 3 0 D a y s

F i sh t yp e ~ L e n g t h i n c r e m e n t D r y w e i g h t i n c r e m e n t R e f e r e n c e( ram~day) (mg /day )

Z 0 .5 1 b - - A r n e m o e t a l . , 1 9 8 2Z 0 .25 1 .31 H ol m e t a l . , 1982Z 0 . 07 - 0 . 68 H o l m , 1985Z 0 . 15 0 . 57 P r e s e n t pa pe rB 0 . 15 0 . 67 H o l m e t a l . , 1982B 0 . 08 c a 0 P r e se n t p a p e r

" Z , f is h f e d l ive z oo p l a nk t on ; B , f is h f e d bo t h d r y f oo d a nd l ive z oop l a nk t on .hF i rs t 20 d ays on ly .

As long as f ry are absorbing yolk , zooplankton seems to have thepotent ia l to en han ce add i t ional growth. Live zoop lankton are thereforereco m m end ed for the f ir s t feeding phase w hen avai lable. How ever , whenyolk absorpt ion is f in ished, opt imal feeding wi th l ive zooplankton isd i f ficult to obta in . T he autho r has no t be en able to ver i fy bet ter growth inolder s tages of sa lmon when zooplankton-fed compared wi th dry fed ,except for a per iod repor ted by Holm and Moiler (1984) . Growthfeeding of sa lmon wi th l ive zooplankton must be cons idered as prob-lemat ic , pr imar i ly due to the prob lem s of achieving suffic ient am ounts offood and op t imal spec ies compos it ion . Th e zoop lank ton feed ing may be


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Atlantic salmo n start-feeding with live zooplank ton 13s t a r te d e a r l i e r th a n c o n v e n t i o n a l d r y f e e d i n g (n o b o t t o m d e p o s i t s ) a n df i n i s h e d a t t h e t e r m i n a t i o n o f th e y o l k a b s o r p t i o n p e r i o d .

A C K N O W L E D G E M E N T SI s h o u l d l i k e t o t h a n k t h e M a t r e A q u a c u l t u r e S t a t i o n ( D e p a r t m e n t o fA q u a c u l t u r e , I n s t i tu t e o f M a r i n e R e s e a r c h , D i r e c t o r a t e o f F i sh e r i e s ) f o rs u p p l y i n g f is h , a n d B r i ti s h P e t r o l e u m N o r g e a.s., t h e D e p a r t m e n t o fF i s h e ri e s B i o l o g y ( U n i v e r si ty o f B e r g e n ) a n d t h e D e p a r t m e n t o f A q u a -c u l t u r e f o r f i n a n c i a l a n d m a t e r i a l s u p p o r t . M s R i t a L e r o y a n d M r J a nT h o r s e n g a v e v al u a b le s u p p o r t d u r i n g fi el d a n d l a b o r a to r y w o r k . T h ea u t h o r i s i n d e b t e d t o M r G e i r J o h n s e n a t th e D e p a r t m e n t o f A n i m a lE c o l o g y , Z o o l o g i c a l M u s e u m ( U n i v e rs i t y o f B e r g e n ), fo r p r o v i d i n g hi su n p u b l i s h e d d a t a o f t h e c l a d o c e r a n d e n s i t i e s i n K v e r n a v a t n e t .D r M a n f r e d M i l i ns k i, D r G u n n a r N a ev d al , M r P e r J a k o b s e n a n dM s K a r i n A . P i t tm a n a r e a c k n o w l e d g e d f o r in s p ir in g d is c u s si o n s a n dh e l p i n p r e p a r i n g d i f f e r e n t v e r s i o n s o f t h e m a n u s c r i p t .

R E F E R E N C E SA rne m o, R. , Puke , C. a nd Steffner, N . G. (1982) . Feeding dur ing the f ir st we eksof young sa lmo n in a pond . Arc. Hydrobiol. , 8 9 , 2 6 5 - 7 3 .Dill , L. M. (1983) . A da pt iv e f lexibi li ty in the foraging beh av ior of f ishes. Can. J .Fish. Aquat. Sci. , 4 0 , 3 9 8 - 4 0 8 .Fast , A. W. (1978). A Floa ting Sys tem fo r Rear ing C o ldwater Fish in T herm al lyUp we ll ing B od ies o f Water. Lim nologica l Assoc . U SA (mimeogr. ).Han sen , T. and Tor r i ssen , O. (1984) . Ar t i fi c ia l ha tching subs t ra te in th e m assrear ing of l a rva l At lant ic sa lmon (Sa lm o sala r) . Coun. Meet ., In t. Coun.Explor. Sea, 1984, F:3 0 (mimeogr .) .Ho lm, J . C. (1985) . Live and f rozen f reshw ater zoo plan kton as a l t e rna t ive s ta r t-feeding d ie t s for A t lantic sa lm on in t rays. Coun. Meet. , Int . Coun. Explor. Sea, 98,5, F: 15 (m imeog r.).Ho lm , J. C . ( 1986) . Rev i ew on expe r imen t s on use o f zoop l ank ton a s food i nsa lmo nid sm ol t production .. Aq uac u l tura l Eng ineer ing , 5( 1 ), 3 3- 47 .Holm, J . C. and Moi le r , D . (1984) . Growth and prey se lec t ion by At lant icsa lmon year l ings reared on l ive f reshwater zooplankton . Aq u a c u l tu r e , 43 ,

4 0 1 - 1 2 .Ho lm, J . C. , Han sen, T. and M oiler , D. (1982) . Star t feed ing of salmo nids withl ake zoop lank ton . Coun. M eet., Int . Cou n. Explor. Se a, 1982, F:36 (mimeogr.) .Holm, J . C. , Jakobsen , E and Johnsen , G. (1985) . Increased growth ra te inAt lant ic sa lmon par r by us ing a two-colour d ie t . Coun. Meet. , Int . Coun.Explor. Sea, 1985, F: 17 (mimeo gr.).Ivlev, V. S. ( 196 1 ). Ex per im en ta l Eco logy o f the Feeding o f F ishes, Yale Un ive r -s ity P re ss , N ew H aven and L ond on .


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14 J.C. HolmLiUehammer , A . ( 1973). A n i nvest iga t ion o f t he food o f on e - to - four -mon th -o ldsa lmon f ry ( Sa l m o s a l ar L . ) in the Riv er Sundals lAgen, W est Norway . Norw. J .Zoo l . , 2 1 , 1 7 - 2 4 .M ilinski, M . (1982) . O pt im al foraging: the inf luenc e of int raspecif ic co m pe t i t ionon d ie t se lec t ion . Behav. Ecol. Sociobiol . , 1 1 , 1 0 9 - 1 5 .Mi linski, M. and L6 w ens te in , C. (1980) . O n pred a tor se lec t ion againstabnorm al i ti es of mov em ent . A tes t of an hypothes i s . Z. Tierpsychol. , 53,3 2 5 - 4 0 .Paul, A . J., Ho od , D. W . and Ne ve , R. A . (1976) . A note o n rear ing juveni lec h u m s a l m o n , Oncorhynchus ke ta , in an artificial up w ell ing system. A q u a -culture, 9 , 3 8 7 - 9 0 .Pepp er , V. A . , Nichol ls , T. and Ol iver , N. E (1983) . A t lant ic salm on fry rear ing

e x p e r i m e n t s i n N e w f o u n d l a n d d u r i n g 1 9 8 2 . Coun. Meet. , Int . Coun.Explor. Sea, 1983, M : 14 (mimeogr.) .R eine r tsen , H. , A una as, T. , G jovik, J . A. , Jensen , A. , N~ess, B. and Olsen , Y.(1984) . Fo r sok r eed opp f r r i ng av l akseyngel r eed dy rep l ank ton somfr rgrunnlag (Sta r t f eeding of At lan t ic sa lmon wi th zooplankton) . N o r s kFiskeoppdrett , 1984( 5 ), 28 -3 1 ( in Norw egian).Scheibling, R. E. (1984) . P red at ion by roc k crabs (Ca nce r i rroratus) on d i seasedsea urchins (Strongylocentrotus droebackiensis) in Nova Scot ia . Can. J. Fish.Aquat . Sci . , 4 1 , 1 8 4 7 - 5 1 .U rquha r t , D . L . and B arna rd , D . R . ( 1979) . G row th o f pen r ea r ed p ink sa lmo nf r y Oncorhynchus gorbuscha, f eed ing on ava i l ab l e mar ine zoop l ank ton .Aquacu l t ur e , 1 7 , 2 5 1 - 6 .Visser, M. (1982) . Prey se lec t ion by the three-sp ined s t ick leback (Gasterosteusaculeatus L.) . Oecologia (Berl .) , 5 5 , 3 9 5 - 4 0 2 .

holm 1987 aquacultural-engineering

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