moore 1986 aquacultural-engineering

7/28/2019 Moore 1986 Aquacultural-Engineering

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Aquacultural Engineering 5 i 1986) 123-133

Input o f O rgan ic M ater ia l s in to Aq uacu l ture Sys tems:E m p h as is on F e e d in g S e m i -I n t e n s ive S ys t e m sLori Barck M oore

Aquaculture Research P rogram, Department of Anim al Sciences.Universityof H awaii, Ho nolulu. Haw aii 9682 2. USA

A B S T R A C TThe l imi ts o f po nd p roduct ion a t td the degree o f po nd chemica l an dbiological stabil i ty are dependent upon the quali ty and quanti ty ofinputs to the system, the dem and s m ade on the system, and the natureo f the b io log ica l popu la t ions in the po nd sys tem, in terdependen t todif fering degrees. The goal is to m axi m ize the ef ficiency o f the f low o fenergy at td nutrients tow ard the anim al output . In extensive systems,energy and nutrient f lo w are depende nt on l ight a t td carbon dioxide,nutr ient cycling, proliferation an d decay rates o f biological po pu latio nsan d the im pac t o f grazing by the cultured species. In in tensive systems,nu tr ien t needs must be m et exogenously in comple te form and a l lwastes removed. O ptimiz ation o f inputs to sem i- intensive systems, inwhich autotrophic or heterotrophic natural productivio ' p lay only apart ial role in supplying required nutrients and energ3, fo r culturedan im al growth, d epend s on the relat ionship between the an im al stand-ing crop an d grazing pressure an d pond-specif ic breakp oints in theconcentration o f grow th l imit ing nutrients.

I N T R O D U C T I O NT h e l i m it s o f p o n d p r o d u c t i o n a n d t h e d e g r e e o f p o n d c h e m i c a l a n db i o l o g i c a l s t a b i l i t y a r e d e p e n d e n t u p o n t h e q u a l i t y a n d q u a n t i t y o fi n p u ts t o t h e sy s t em , th e d e m a n d s m a d e o n t h e s y s te m , a n d t h e n a t u r eo f t h e b i o l o g i c a l p o p u l a t i o n s i n t h e p o n d s y s t e m . A s i n a n y s y s t e m ,e l e m e n t s a r e i n t e r d e p e n d e n t to d i f fe r in g d e g r e e s . I n a q u a c u l t u r es y s t e m s t h e r e a r e p a r t i c u l a r a n i m a l t i s s u e o u t p u t s t o b e m a x i m i z e d

123Aquacultural Engineering 014 4-860 9/86/S0 3 .50- Elsev ier Appl ied S c i e n c eP u b l i s h e r s L t d , E n g l a n d , 1 9 8 6 . P r i n t e d i n G r e a t B r i t a i n


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124 L . B . M o o reand pa r t i cu l a r b io loNca l (p rov i s ion o f r equ i r emen t s ) and non-bio loN cal (cos t and ava i lab i li ty) qua l i f i ca t ions p laced o n the inputs .T he goal is to m aximize the e f f ic iency of the f low of energy andnu t r i en t s t oward t he an ima l ou tpu t . The p r imary source o f i n i t i a lnut r ien t en t ry in to any g iven aquacul ture sys tem i s re la ted to thein t ensi ty o f t he sys tem. In ex t ens ive syst ems , e n e r~ and nu t r i en t fl oware de pen den t i n i ti a ll y on l igh t and ca rbo n d iox ide fo r au to t roph i cgrowth . Nut r ien t cyc l ing , pro l i fe ra t ion and decay ra tes of b io logica lpop u l a t i ons and t he imp ac t o f g r azing by t he cu l t u r ed spec ie s p rov idethe subsequent ba lance in the sys tem. In in tens ive sys tems , wherenatura l prod uct iv i ty is re la t ive ly unav ai lab le wi th respec t to the ene rgyand nu t r i en t needs o f the cu l t u r ed spec ie s , t hese needs m us t be exo-genous ly met in comple te form. Sys tems which l i e be tween these twoex t r emes , i n wh ich au to t roph i c o r he t e ro t roph i c na tu ra l p roduc t i v i t yplay a par t i a l but in com ple te ro le in supply ing suf fic ient nut r ien t s an dene rgy t o max imize cu l t u r ed an ima l g rowth , a r e pe rhaps t he mos td i f fi cu l t to m anag e ef f ic iently . Sem i- in tens ive sys tem opt im iza t iondepends on t he r e l a t i onsh ip be tween t he an ima l s t and ing c rop i n t hesys tem and ( 1) spec ies -spec i f ic graz ing pressure , and (2) pond -spec i f icb reak po in t s i n t he con cen t r a t i on o f g rowth- l imi t i ng nu t r ien t s. Thes ede t e rm ine how the ava i lab i li ty and su f fi c iency o f na tu ra l f oods va ry a sanim al s tandin g crop s ize var ies .The ba l ance o f de l i ve ry and u t i l i za t i on o f f eed i npu t s i n to aqua -cu l tu r e sys t ems is d i r ec t ed p r imar i l y a t mee t i ng nu t r i en t r equ i r emen t sof the cul tured spec ies , but a l so com pr i ses bro ad impl ica t ions for thesys tem as a who le . T he re a r e m ul t ip l e in t e r ac t ions o f app l ied o rgan i cand i no rgan i c ma te r i a l s w i th d i f f e r en t a spec t s o f t he env i ronment ,i nc lud ing t he d eve lopm ent o f na tu ra l f ood spec ie s . Th e re a r e a l so t henu t r i en t impac t s t he env i ronment and t he cu l t u r ed spec i e s have oneach o the r . Th ese f ac to r s d i c t a te t ha t t he app l i ca t i on o f f eed be con-s idered a lways as a sys tem i ssue , whatever the s i t e des ign or foodrequi rem ents of the spec ies cu l tured .T h e i n s i t u d e v e l o p m e n t o f n a t u ra l f o o d f o r c o n s u m p t io n b y c ul-t u red he rb ivo rous spec i e s i nc ludes p ro l i f e r a t i on o f a lga l and macro -phyt ic growth , dr iven by l ight , carbon d ioxide (a tmospher ic andresp i r a to ry ) , and so lub l e n i t rogenous and mine ra l compounds . Thesupply of nut r ien t s for such na tura l pro l i fe ra t ion i s a f fec ted by thepresence o f o the r spec ie s wh ich may con sum e the same foods o r con-sume the compe t i t o r s o f t hose foods , by t he nu t r i en t s i n t he was t e s


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Input of organic materials into aquaculture systems 125p r o d u c e d b y o t h e r s p e c i e s , a n d b y t h e n u t r i e n t s f r o m t h e l e a c h i n g o fs o l u b l e s f r o m an y o r g an i c m a t e r i a l ap p l i ed t o t h e s y s t em ( F ig . 1 ). S i n cei n t e r ac t i o n s w i t h a ll s p ec i e s , i n c l u d in g m i c r o b es , m ay a f fec t g r o w t h o fa q u a t i c a u t o t r o p h s , t h e p a r t i c u l a r m i c r o b i a l a n d o t h e r h e t e r o t r o p h i cs p e c ie s h a v e a n i m p a c t o n t h e g r o w t h o f f o o d f o r c u l tu r e d h e r b i v o r e san d t h e s t ab il it y o f t h e s y s t em.C u l t u r e d d e t r i t i v o r e s , o m n i v o r e s a n d c a r n i v o r e s c o n s u m e n a t u r a lh e t e r o t r o p h i c p r o d u c t i v i t y a s we ll, t h e g r o w t h o f wh i ch is ag a i n re l a t edt o n u t r ie n t s p r o v i d e d b y a n u m b e r o f t h e s o u r c e s in th e s y s te m , i n c lu d -i n g t h e s e n e s c e n t t i s s u e a n d w a s t e s f r o m b o t h a u t o t r o p h s a n d h e t e r o -t r o p h s , i n c l u d i n g t h e cu l t u r ed s p ec i e s . M i c r o b i a l p r o l i f e r a t i o n is ag a i nk e y s i n c e i t i s t h e c o r n e r s t o n e o f d e t r i t a l d e v e l o p m e n t , c o n s u m e d b y

,N D S .,G.TSOLUBILIZATION t DET RITALIN WATERCOLUMN APPLIED ORGANICMATFIER STIMULATION"

DIRECT CONSUM PTION

SOLUBLE NUTRIENTS FISH WASTESPHYTOPLANKTON FE ED ING BIVALVES FEEDINGI . L sWASTES ] ~ FEE DING

Fig. 1 . Fate of app l ied org anic mat te r in aqua t ic sys tems. (From Mo ore , 1985.)


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126 L. B. Moorecu l t u red de t r i ti vo re s and b y me io fauna which a re i n t u rn consu m ed byben th i c omnivores and ca rn ivores .The organic res idues ava i lab le in the extens ive aqua t ic sys teminc lude an ima l exc re t a and exoske l e tons , p l an t exuda t e s such a samino ac ids , shor t cha in ac ids , ca rbohydra t e s , po lysaccha r ides andglycerol re leased f rom a lgae (Lynch and Poole , 1979) . A t dea th , p lant sand an ima l s re l ea se so lub le and pa r t i cu l a te o rgan i c com pou nds . Asso-c i a t i ons (pe l a~c o r ben th i c ) be tween g roups o f mic roorgan i sms canresu l t in t he cyc l i ng o f com po un ds which co u ld be con t ro l l i ng f ac to r sin the success ion of spec ies in p lan kto nic b loom s. For exam ple , a la rgenumber of p lanktonic a lgae spec ies t es ted requi re v i t amin BI2 forgrowth , wh i le o the r a lga l spec ies an d bac te r ia w i ll re lease it.Thus i n na tu ra l and commerc i a l pond sys t ems , nu t r i en t s con-t inua l ly cyc le t h rough a p roces s o f so lub i l i za t ion and i nco rpora t i onin to t he t i s sue o f au to t roph i c and he t e ro t roph i c spec i e s a t s eve ra ln iches and t rophic l eve l s . The d i f fe rent spec ies therefore not onlymutua l l y supp or t one a no the r bu t a l so com pe te fo r nu t r ien t s ando the r r e sources . The en t ry o f any app l i ed o rgan i c ma te r i a l i n to t hesys t em, s i nce i t con t a ins no t on ly nu t r i en t s d i r ec t l y consumed byhigher spec ies but a l so so luble ma ter ia l s wh ich leach in to the sys tem,unco nsum ed pa r ti c le s wh ich seed he t e ro t roph i c act iv i ty , and a subse -quent demand on oxygen by i t s decay , a f fec t s a l l l eve l s of nut r i en tava i lab il i ty and organ ism gro wth in such a sys tem.

E X T E N S I V E S Y S T E M SIn extens ive sys tems , the nut r ien t s cyc le amongs t the consumers unt i lthey reach the cul tured spec ies ; the major cons t i tu t ive inputs a reca rbon , i n the fo rm o f ca rbo n d iox ide f rom the a i r -w a t e r i n t e rf ace andhe t e ro t roph i c r e sp i r a t i on , and o rgan i c and i no rgan i c ma te r i a l s ,p r e sen t a t t he wa t e r - ea r t h i n t e r f ace . The cu l t u r ed spec i e s subs i s t onna tura l ly occur r ing foods , which have a b io logica l l imi t to the speedwi th which t hey can r ep roduce and a nu t r i en t l im i t t o t he ex t en t t owhich they can d o so . Th is l imi ts the s tand ing c ro p (b iom ass /uni t a rea)o f cu l t u r ed spec i e s wh ich can be suppor t ed by t h i s na tu ra l p roduc -t iv i ty . Th is l imi t var ies wi th spec ies a nd the i r graz ing sp eed and habi ts .

A t r e m e n d o u s a m o u n t o f m a t e r i a l m a y b e p r o c e s s e d b y d e p o s i tfeeders ; O du m (1970) c a lcula tes tha t de t r i t ivoro us fi sh may process as


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Inp ut o f organic materials into aquaculture O'sterns t 2 7m u c h a s ~ t o n n e o f m a t e r ia l s i n o n e y e a r. A lth ou gJ a o n e ~ a m o fde t r i tus m ay con ta in as m an y as 5 x 10 s to 10 ~ m ic rob ia l ce ll s,F i n d l a y a n d T e n o r e ( 1 9 8 2 ) p e r f o r m e d m a s s b u d g e t s t o i n d i c a t e t h a tb a c t e r i a a l o n e c a n n o t s u p p o r t t h e e n e r g y r e q u i r e m e n t s o f d e p o s i tf e e d e r s . T h e r e f o r e a l o n g w i t h t h e c o n s u m p t i o n o f v e g e t a t i v e m a t t e ra n d m a s s e s o f d e t r i t a l a g g r e g a t e s , t h e b r o w s i n g c r u s t a c e a n a n d f i s hr e li e s u p o n t h e l i vi n g m e i o f a u n a o f t h e b e n t h o s . T h e g o a l o f m a n a g e -ment o f ex tens ive sys tems i s to a l low a na tu ra l ba lance to es tab l i shi ts el f, th e m a i n p r o v i s o b e i n g t h e a p p r o p r i a t e l y l ow s t o c k i n g t o e n s u r et h a t t h e d e p o s i t i o n o f e n e r g y a n d n u t r i e n t s f r o m n a t u r a l f o o d s i n t o th ec u l t u r e d s p e c i e s c a n b e s u p p o r t e d b y t he n a t u r a l i n p u ts , g r o w t h r a te sa n d i n t e r a c t i o n s o f p o n d o r g a n i sm s .M an y ex tens ive sys tems a re in p rac t i ce s t im ula ted bv fe r t i li za t ion o fthe au to - and lower he te ro t roph ic o rgan isms . Inorgan ic fe r t i l i ze r wi l ls t i m u l a t e p h y t o p l a n k t o n a n d o t h e r a u t o t r o p h i c g r o w t h . L o w q u a l i t yo r g a n i c m a t e r ia l s ( m a n u r e ) c a n s t im u l a t e d e v e l o p m e n t o f q u a l i ty f o o dmate r ia l s . Manures con ta in und iges ted o rgan ic feeds tu f f s , l iqu idn i t r o g e n o u s w a s t e s a n d e n d o g e n o u s s e c r e t i o n s f r o m t h e a n i m a l a n d ala rge pe r cen tage o f m ic rob ia l cells . T he m anu re i t se l f a s p rese n ted tothe pond i s no t a h igh qua l i ty feed fo r c rus tacea o r f i sh (Schroeder .1978) bu t mic rob ia l co lon iza t ion o f o rgan ic mat te r wi l l fo rm a de t r i t a lpa r t i c le o f d i f fe ren t nu t r i en t compos i t ion f rom the o r ig ina l ma te r ia l .E x o c e l l u l a r m i c r o b i a l e n z y m e s h y d r o l y z e o t h e r w i s e i n d i g e s t i b l ef i b r o u s s u b s t a n c e s a n d m a k e t h e m a v a i l a b l e t o t h e c o n s u m e r ( F e n c h e la n d J o r g e n s e n , 1 9 7 7) . S i m i la r ly , l ow q u a l i t y p r o t e i n a n d n o n - p r o t e i nn i t r o g e n s o u r c e s m a y b e m e t a b o l i z e d b y m i c r o b e s a n d i n c o r p o r a t e din to the i r ce l lu la r (h igher qua l i ty ) p ro te ins . Thus , b io log ica l va lue o ft h e m a t e r i a l w i l l b e e n h a n c e d w h e n h e t e r o t r o p h i c c o l o n i z a t i o n o fp l a n t m a t e r ia l t r a n s f o r m s t h e p r o t e i n q u a l i ty f r o m p l a n t to a n i m a lp r o t e i n , a n d i n c o r p o r a t e s t h e n u t r i e n t s o f o t h e r w i s e r e f r a c t o r y f i b e rc o m p o n e n t s i n t o a m o r e d i g e s t ib l e f o rm .One o f the major benef i t s in the ex tens ive sys tem i s tha t was tes a red i lu ted due to the l a rge a rea : an im al ra tio . Th is a l lows fo r mo re com -p le te u t i l i za t ion o f was tes by o the r pond spec ies , s ince the sys tems don o t n e e d t o r e m o v e s u c h n u t r i e n t s t o m a i n t a i n a c c e p t a b l e w a t e rq u a l i t y . T h i s m a y r a p i d l y c h a n g e w h e n a n y q u a n t i t y o f o r g a n i cm a t e r i a l is a d d e d t o t h e p o n d , d e p e n d i n g o n i ts c h e m i c a l a n d b i o lo g i-c al o x y g e n d e m a n d .


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12 8 L. B. Moore

I N T E N S I V E S Y S T E M ST he goa l o f in ten s ive sys tem s is to c re a te a ve ry . l a rge s tand ing c ro p o fcu l tu re d spec ies . The co l lec t ive metabo l ic ac t iv i ty is so g rea t tha tw a s t e s a r e p r o d u c e d i n g r e a t v o l u m e s ; th e r e a r e g e n e r a l l y n o o t h e rh e t e r o t r o p h s a n d f ew a u t o t r o p h s t o u t il iz e t h e w a s te s . T h e e n e r g y a n dn u t r i e n t s i n t h e w a s t e s m u s t t h e r e f o r e b e r e m o v e d u n u s e d b e f o r e t o x icc o n d i t i o n s b u i l d u p i n t h e s y s t e m . T h u s , n o f o o d w e b s d e v e l o p , n o rc o u l d t h e y k e e p p a c e w i t h th e n u t r i e n t n e e d s o f a la r g e s t a n d i n g c r o p .T h e e n t i r e n u t r i e n t n e e d s o f t h e c u l t u r e d s p e c i e s m u s t b e m e t w i t hh igh qua l i ty app l ied feed , in a food cha in typ ica l o f c lass ica l t e r res t r ia lagr icu l tu ra l an imals .

T h e e n g i n e e r i n g d e m a n d s o n s u c h s y s t e m s a r e t h e r e f o r e q u i t es o p h i s t i c a t e d . I n t e n s i v e s y s t e m s r e q u i r e a h i g h d e g r e e o f w a s t em a n a g e m e n t a n d n u t r i e n t d e l i v e r y t e c h n o l o g y , a t h i g h c o s t . R a c e w a yt r o u t c u l t u r e a n d t h e S h i g u e n o s y s t e m o f s h r i m p c u l t u r e a r e s u c hi n t e n s i v e s y s t e m s . D e v i c e s s u c h a s d e m a n d o r a u t o m a t i c f e e d e r s , o rm a n a g e m e n t m e t h o d s f o r c l o s e l y m o n i t o r i n g f e e d c o n s u m p t i o n , a r eu t i l i zed to min imize was te o f feed . Th is i s c r i t i ca l , s ince no t on ly i ss u c h h i g h q u a l i ty f e e d e x p e n s i v e , b u t a n y d e c a y i n g f e ed c o n t r i b u t e s t oo x y g e n d e m a n d a n d b u i l d u p o f p o t e n t ia l ly h a z a r d o u s n i tr o g e n o u sp r o d u c t s a n d m i c r o b i a l g r o w t h . C h e m i c a l b i n d e r s t o e n h a n c e w a t e rs tab i l ity o f feed , and fa l se tank b o t tom s to min im ize bu i ld -up o fu n e a t e n f o o d a l s o d i s c o u ra g e d e v e l o p m e n t o f n o n - p r o d u c t i v e n u t r i e n tl e a c h in g a n d h e t e r o t r o p h i c a c ti v it y .

S E M I - I N T E N S I V E A N D S E M I - E X T E N S I V E S Y S T E M SS y s t e m s w h i c h f a l l b e t w e e n t h e s e t w o e x t r e m e s a r e t h e m o s t c o m p l e xb e c a u s e t h e y h a v e b o t h p a t h w a y s o f f o o d u t il iz a t io n , d i r e c t c o n s u m p -t i o n a n d t h a t v i a t h e f o o d w e b , w h i c h m u s t b e m a n a g e d ( F i g . 1 ) . T h ed e g r e e t o w h i c h e a c h i s o p e r a t i v e i n a g i v e n s y s t e m d e p e n d s o n t h en a t u r a l p r o d u c t i v i t y o f t h e p o n d , t h e f o o d c h o i c e s a n d p h y s i o l o g i c a lg raz ing ab i li ty o f the cu l tu red spec ies an d the s tand ing c rop s ize o f,a n d h e n c e g r a z i n g p r e s s u r e i m p o s e d o n t h e s y s t e m b y , t h e c u l t u r e dspecies .

T h e e f f i c i e n t s t r a t e g i e s f o r m a n a g i n g s u c h s y s t e m s i n c l u d e s u c hc o m p o n e n t s a s ( 1 ) m a x i m i z i n g u t i l i z a t i o n o f n a t u r a l p r o d u c t i v i t y a s


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Inp ut o f organic materials into aquactdtt~re systems 129l o n g a s it is a d e q u a t e t o m e e t n u t r i e n t r e q u i r e m e n t s o f th e s t a n d i n gcrop , (2 ) supp ly ing low qua l i ty mate r ia l s ( fe r t i l i ze r s ) to s t imula te thep o n d s y s t e m , (3 ) a d d i n g o t h e r s p e c i e s w h i c h a r e n o n - c o m p e t i t iv e w i t ht he p r i m a r y s p e c ie s b u t w h i c h m a y m a k e p o n d n u t r i e n t s o u r c e s m o r eava i lab le , and (4 ) us ing app l ied feeds which a re t a i lo red to p rov idew h a t t h e n a t u r a l s y s t e m d o e s n o t .T h e p r e s e n c e o f t h e f o o d w e b s h o u l d b e u s e d t o e n h a n c e e f f i c i e n c yo f a p p l i e d o r g a n i c m a t t e r , n o t r e d u c e i t . T h e a p p l i e d f o o d s h o u l dleach o r be d egra ded by m ic roo rgan ism s ve ry l it tl e i f i t is o f h ighqua l ity . T he feed shou ld b e a l lowed to se~ 'e as a de t r i t a l subs t ra teo n l y if t h e r e s u l t in g e n c o u r a g e m e n t o f n a t u r a l p r o d u c t i v i ty i s o f h i g h e rqua l i ty than the app l ied feeds tu f f . I f , however , the pa r t i c le be ingc o l o n i z e d b y m i c r o b e s o r c o n s u m e d b y m e i o f a u n a i s a l r e a d y o f h i g hnu t r ien t qua l i ty , the re i s a loss o f e f f i c iency in hav ing the energy andn u t r i e n t s c y c l e t h r o u g h o n e o r m o r e t r o p h i c l e v e l s b e f o r e b e i n g c o n -s u m e d b y th e c u l t u r e d s p e c ie s .G o y e r t a n d A v a u l t (1 9 7 7 ) e m p h a s i z e d t h at , in e v a lu a t i n g t h e u ti li tyo f s u p p l e m e n t a l f e e d s f o r d e t r it i v o r e s , 'o n e m u s t c o n s i d e r t h e i r in i ti a lnu t r i t iona l va lue as we l l a s the i r va lue a f te r en t rance in to the de t r i t a lsys tem ' . D isperse d par t i c les o f o rgan ic m at te r app l ied to the ponds ,i n c l u d i n g f e e d s i n s e m i - i n t e n s i v e s y s t e m s , w i l l p r o v i d e a t t a c h m e n ts i t e s f o r m i c r o b e s i n a m a n n e r a n a l o g o u s t o o t h e r e c o s y s t e m s w h e r ea l loc h tho no us o rgan ic p lan t m at te r ( e .g . l ea f fa ll , m acro phy t ic pa r -t i c les ) s inks to the pond bo t tom and fo rms de t r i tus and then i s im-m e d i a t e l y c o l o n i z e d b y m i c r o b e s ( F l o o d g a t e , 1 9 7 2 ; O l a h , 1 9 7 2) .S a p r o p h y t i c f u n c t i o n s p r o c e e d w h e n s u f f i c i e n t m i c r o b i a l p o p u l a t i o n sb e c o m e e s t a b l i s h e d o n t h e p a r t i c l e s ( H a r g r a v e , 1 9 7 2 ; S a u n d e r s ,1 9 7 5 ) . T h e e p i p h y t i c g r o w t h c a n b e s t r i p p e d m a n u a l l y o r w i t h i n t h ed iges t ive trac t o f the de t r i t ivore (Schroeder , 1978) .W h e t h e r t h e e p i p h y t i c g r o w t h o r t h e o r i g i n a l s u b s t r a t e p a r ti c le i s o fm o s t n u t r i t i o n a l v a l u e d e p e n d s o n t h e s u b s t ra t e i t s e lf a n d t h e c o n s u m -i ng s p e c ie s . I n v e r t e b r a t e c o n s u m p t i o n o f tw o l e a f t y p e s in c u b a t e d w i t hth ree inver tebra te spec ies was t e s ted in cages in runn ing s t reams( H e r b s t , 1 9 8 2) . T h e c r a n e f l y l a r v a e a n d c a d d i s f l y t e st e d c o n s u m e dm o r e o f o n e l e a f t y p e ( s i l v e r m a p l e ) t h a n a n o t h e r ( c o t t o n w o o d ) , b u tt h e a m p h i p o d s h o w e d n o d i f f e r e n ce . O f t h e l e av e s th e m s e l v e s, c o t to n -w o o d c o n s u m p t i o n i n c r e a s e d w i t h t i m e b u t s i l v e r m a p l e d i d n o t . T h es a m e a u t h o r s u m m a r i z e s s i m i l a r w o r k b y o t h e r s w i t h d o z e n s o f


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130 L. B. Moore

s p e c ie s a n d s u b s t r a t es , a n d e m p h a s i z e s t h e i m p o r t a n c e o f ' c o n d i t io n -ing pe r iod ' , tha t i s , the t ime to deve lop funga l and bac te r ia l g rowth onl e a v e s , r e q u i r e d t o e n h a n c e i n v e r t e b r a t e f e e d i n g . T h e c o n d i t i o n i n gw i ll v a r y w i t h th e c o m p o s i t i o n a n d p h y s i c a l s t ru c t u r e o f th e s u b s t r a tei tse lf , henc e the d i f fe ren t co nsu m er resp ons e to two lea f t-ypes (Herbs t ,1 9 8 2 ). F i n d l a y a n d T e n o r e ( 1 9 8 2 ), i n a n e l e g a n t s tu d y u s i n g d i f fe r e n -t ia l ly r a d i o - l a b e ll e d p l a n t s u b s t r a t e s a n d s u b s e q u e n t d e t r i ta l g r o w t h ,d e m o n s t r a t e d t h a t t h e p o l y c h a e t e C api te l la cap i ta ta d e r i v e d a m a j o rpor t ion o f i t s n i t rogen f rom the subs t ra te when the subs t ra te i s a sea -w e e d a n d f r o m t h e c o lo n i z i n g m i c r o b e s w h e n t h e s u b s t r a t e is a m a r s hgrass.T h u s i t i s n o t a s i m p l e m a t t e r t o p r o v i d e t h e c o r r e c t i n f u s o r i a f o ro p t i m a l c o n s u m p t i o n b y th e c u l t u r e d s p e c ie s . T h e s y s t e m m a y a c h i e v ea b a l a n c e w i t h o u t t h e o p e r a t o r k n o w i n g t h e s p e c i f i c i n d u c t i o n soccur r ing . Al te rna t ive ly , the idea l subs t ra tes and co lon iz ing spec iesm a y b e e x p e r i m e n t a l l y d e t e r m i n e d , a s w e l l a s t h e b e s t m a n n e r i nw h i c h to m a x i m a l ly d r i v e t h e s y s t e m t o g e n e r a t e t h e d e s i r ed n a t u r a lp r o d u c t i v i t y w h i l e h o l d i n g t h e s y s t e m i n b a la n c e .U n t i l su c h c o m p l e t e k n o w l e d g e o f d ri v in g e c o s y st e m c o m p o n e n t s isa c h i e v e d , p o n d m a n a g e m e n t s y s t e m s c a n n e v e r t h e l e s s f o l l o w t h eg e n e r a l p r i n c i p l e o f m a x i m i z i n g a v a il a b le n a t u r a l p r o d u c t i v it y . W h e n apon d i s in i ti a l ly s tock ed wi th smal l , you ng an imals , the resu l t i s usua l lya s m a l l s t a n d i n g c r o p ; a l t h o u g h t h e n u t r i t io n a l n e e d s o f y o u n g g r o w i n gan imals a re h igh , they can a t th i s po in t be met to a l a rge ex ten t byna tu ra l g raz ing . In a ba tch ha rves t sys tem , where the in i t ia l s tocke dcoh or t g rows to ha rv es t s ize wi th in a s ing le pond , the g raz ing p ressureon na tu ra l foods inc reases as the s tand ing c rop g rows . As a resu lt , f eedm u s t b e a p p l i e d t o t h e s y s t e m t o s u p p l e m e n t t h e n a t u r a l f o o d s .A l thoug h i t ma y no t be p oss ib le to iden t i fy the exac t po in t a t which ag i v e n n u t r i e n t a s s u p p l i e d b y n a t u r a l f o o d s b e c o m e s l i m i t e d , t h eg e n e r a l p ri n c i p l e o f c o m p l e m e n t a r i t y o f a p p l ie d a n d n a t u r a l f o o d s c a nbe fo l lowed .I s rae l i f i sh cu l tu re o f ca rp and t i l ap ia ( in mono- and po lycu l tu re ) i sa n e x c e l l e n t e x a m p l e o f in c r e a s i n g t h e c a r r y i n g c a p a c i t y o f a p o n d b yi n d u c t i o n o f n a t u r a l o r g a n i s m s a n d o f u s i n g a p p l i e d f e e d s t o c o m p l e -ment the l eve l and qua l i ty o f ava i l ab le na tu ra l f eeds (Marek , 1975 ;Hepher , 1979) . In unfe r t i l i zed ponds , the ca r ry ing capac i ty in ca rpm ono cu l tu re is abo u t 100 kg h a - ~, ye t w hen fe r t i li zed i t is abo u t 4 60k g h a - ~ . I n p o l y c u t t u r e , w h e r e g r a z i n g p r e s s u r e i s d i s t r i b u t e d a m o n g


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In pu t o f organic materials into aquaculture s3"stems 131d i f f e re n t f e e d in g n i c h e s a n d w a s t e s f r o m o n e s p e c i e s c a n f e e d a n o t h e r ,the ca r ry in g capac i ty o f a fe r t i l ized po nd is ab ou t 600 kg ha - ~. Th is i sn o n - s p e c i f i c i n d u c t i o n , a c c o m p l i s h e d w i t h i n o r g a n i c f e r t i l i z e r o rm a n u r e . A s t h e s t a n d i n g c r o p o f f i s h i n c r e a s e s , e v e n s t i m u l a t e d( f e r t i l i z e d ) n a t u r a l p r o d u c t i v i t y b e c o m e s l i m i t e d a n d s u p p l e m e n t a lfeeds a re app l ied . S ince the na tu ra l pond o rgan isms which a re s t i l lava i l ab le (a lbe i t l imi ted) fo r feed a re h igh in p ro te in :energy ra t io ,ene rgy i s the f i r s t l imi t ing fac to r ; the re fo re the f i rs t supp lem enta l f eedsu s e d a r e g ra i n s , p r i m a r i l y e n e r g y r a t h e r t h a n p r o t e i n s o u r ce s . A s t h es t a n d i n g c r o p i n c r e a s e s f u r t h e r ( > 7 0 0 k g h a - t), a n i n c r e a s i n g p r o p o r -t i o n o f t h e g r a i n s a r e r e p l a c e d w i t h h i g h e r p r o t e i n f o r m u l a t e d f e e dpe l le t s (Hepher and Prug in in , 1981) . Thus , the expens ive l a t t e r d ie t i sn o t u t i l i z e d b e f o r e i t i s r e q u i r e d a n d m a x i m u m a d v a n t a g e i s t a k e n o fe x i s ti n g a n d i n d u c e d n a t u r a l f o o d s .T h e s a m e p r i n c i p le c a n o p e r a t e i n s e m i - i n t e n s iv e s h r i m p a n d p r a w np o n d c u l t u r e . T h e c o n t r i b u t i o n o f p o n d f l o r a a n d f a u n a t o t h e d i e t o fthese an ima ls i s wide ly ack now ledg ed (W eidenbach , 1982). A t t r ad i -t iona l commerc ia l s tock ing dens i t i e s fo r up to mid-s ize f reshwate rp r a w n s , a m i d - r a n g e p r o t e i n f e e d ( 2 5 - 3 0 %) a p p e a r s t o b e a d e q u a t ef o r p r a w n s r a i s e d i n m u d b o t t o m e d p o n d s a n d s u p e r i o r t o p l a n tp r o d u c t s o f l o w e r q u a l i t y ( M o o r e a n d S t a n l e y , 1 9 8 2 ) . T h i s h a s b e e nshown bo th p rac t i ca l ly and exper imenta l ly . In t r i a l s us ing i soca lo r icfeeds va ry ing in p ro te in l eve l , smal l s t and ing c rops (20 gm-- ' ) o f thep r a w n M a c r o b r a c h i u m r o s e n b e r g i i were shown to g row equa l ly we l lw h e t h e r t h e y w e r e f e d d i e ts o f 1 3 - 5 0 % p r o t e i n o r s u b s i st e d o n n a t u ra lp o n d f o o d s a l o n e ( i. e. w e r e u n f e d ). H i g h e r s t a n d i n g c r o p s ( 1 0 0 - 2 0 0 gm -2) d id no t ach ieve op t im um grow th i f unfed , bu t d id g row equa l lyw e ll o n f e e d s c o n t a i n in g 1 3 - 5 0 % p r o t e in . A t 2 0 0 - 3 0 0 g m -2 , h o w -ever , these an imals requ i red a t l eas t 30% pro te in to sus ta in bes tg r o w t h a n d d i d n o t g r o w a t a ll o n n a t u r a l f o o d s a l o n e ( M o o r e e t a l . ,1984) . Th is i s no t to say tha t the nu t r i en t r equ i rement o f p ro te in fo rthese an im als fa ll s wi th in th is r ange ; th i s is to be de te rm ined in nu t r i -t iona l tr i a ls whe re no na tu ra l foods a re p resen t . I t does imply tha t f eedm a n a g e m e n t s c h e m e s i n s e m i - i n t e n s i v e a n d s e m i - e x t e n s i v e s y s t e m s ,even i f f eed qu an t i ty i s ad jus ted fo r inc reas ing b iom ass , m ay need a l sot o v a r y t h e q u a l i ty o f th e f e e d . T h o s e s y s t e m s w h i c h p r o v i d e a s in g l em i d - q u a l i t y fe e d f o r t h e d u r a t i o n o f a g r o w - o u t c y c le o f a n i m a l s m a yb e o v e r f e e d i n g a s m a l l s t a n d i n g c r o p a n d d a n g e r o u s l y u n d e r f e e d i n gspec i f ic nu t r i en t s to h igh er s t and ing c rops .


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13 2 L. B. Moore

Pas t a ce r t a in s t and ing c rop s i ze , dens i t y dependen t f ac to r s o the rthan ade qua t e food p l ay an i nc reas ing ro le i n de t e rm ina t i on o f ca r ry -i ng capaci ty . Dec reas ing oxygen and i nc reasing me tabo l i t e p rodu c t i onfor example , wi l l occur , but may be managed wi th water qua l i ty ,m anag em ent t echn iques . M ore d i ff icu l t t o ov e rcom e wi ll be t he b io -logica l and beh avio ra l limi t s to d ens i ty of the cu l tured spec ies .I n c o n c l u s i o n , f e e d d e v e l o p m e n t a n d f e e d m a n a g e m e n t s t r a t e # e sa r e d e p e n d e n t o n t h e e n t i re s y s te m . T h e c o n t r i b u t i o n o f n a tu r a l fo o d smu st be eva lua ted , e i ther q uant i t a t ive ly , by e num era t ing a l l poss ib lenu t r i en t sources, t he i r com pos i t i on and p ro l i f e r a t ion r a te s , o r qua l it a -tively , by expe r im en ta l ly o r o bse rva t i ona l l y de t e rmin ing t he am oun t o fg rowth t hey w il l suppor t . T h i s mus t be co up l ed w i th know ledge o f thenu t r i en t r equ i r emen t s o f t he cu l t u r ed spec i e s , s i nce t he combina t i onof na tura l and appl ied feed wi l l a lways have to meet these needs . Al lappl ied mater ia l mus t of course fa l l wi th in the water qua l i ty manage-m ent co ns t ra in t s of the sys tem. An d lastly , inven tory co nt ro l of s t and-ing c rop s ize (and its co m po nen ts , an im al s ize and dens i ty) is c ri ti ca ls ince the feed management scheme wi l l be t i ed to i t . Moni tor inggrowth and mor ta l i ty v ia sampl ing i s necessary , as i s making andver i fy ing b iom ass p ro jec t io ns on the bas i s of these d a ta . Also , there i sa need to es tabl ish the re la tive con t r ibu t ion tha t form ula ted feed p laysin d i rec t ly nour i sh ing the prawn i t se l f and in enr iching the de t r i t a ll ayer and s t imula t ing the pond food web. Because of th i s , researchs t ra tegies mus t re ly on energy- f low models charac te r i s t i c of ' non-agr icul tura l' d isc ip l ines such as aqu a t ic ecolog y and l imnology; the useof mode l s e m ploy ed i n s t ud ie s o f t e r r e s tr i a l f a rm an ima l s is i napprop -r ia te because these models cons ider energy f low in feeding as a food'cha in ' ( input - - - food- - -anim al - - -output ) . T he energy a nd nut r ien t s inthe f eed app l i ed t o a pond f l uxes t h rough t he pond ' s f ood 'web ' ,i nc lud ing bo th au to t rop h i c f eed ing n i ches (v ia nu t r i en t l each ing) andmic rohe t e ro t roph i c f eed ing n i ches (v i a mic rob i a l co lon i za t i on ) .U l t ima t e ly f eed m ana gem ent s chemes can t he re fo re be des igned to beno t only species specif ic , bu t s ite , system , age and po nd s tage specific .

R E F E R E N C E SFench el, T. M. & Jo rgensen, B. B. (1977). Detritus food chains o f aquatic eco-systems: the role of bacteria. In: A d v a n c e s i n M i c r o b ia l E c o lo g y , Vo l. I, ed.

M. Alexander, Plenum P ress, New York.


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Input of organic materials into aquacu lture systems 133Fi n d l ay , S . & T en o re , K . (1 9 8 2 ) . N i t ro g en s o u rce fo r a d e t r i t i v o re : d e t r i t u ss u b s t r a t e v e r s u s a s s o c i a t ed m i c ro b es . Science, 2 1 8 , 3 7 1 - 3 .F l o o d g a t e , G . (1 9 7 2 ) . T h e m ech an i s m o f b ac t e ri a l a t t a ch m en t t o d e t r i tu s inaquat i c sys tems . D et r i tus and its ro le in aqua t i c ecosy s tem s . Mere. Inst. Ital.Idrobiol., 29 (Suppl . ) , 105-27 .Go yer t , J. C . and Avau l t , J . W. J r . ( I97 7) . Ag r icu l tu ra l by-p rod uc t s as supp le-m e n t a l f e e d f o r c r a ~ i s h , Proc am barus clarki i. Trans . A m . Fish. Soc., 1 0 6 ,6 2 9 - 3 3 .H arg rav e , B . T . (1 9 7 2 ) . A e ro b i c d eco m p o s i t i o n o f s ed i m en t an d d e t r i t u s as afu n c t i o n o f p a r t i c l e s u r f ace a r ea an d o rg an i c co n t en t . Limn. Ocean. . 17,5 8 3 - 9 6 .H e p h e r , B . (1 9 7 9 ) . Su p p l e m en t a ry d i e ts an d r e l a t ed p ro b l em s i n f is h cu l tu re .

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