Bardach 1986 Aquacultural-Engineering

7/28/2019 Bardach 1986 Aquacultural-Engineering

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Aquacul tural Engineer ing 5 (1986) 287-300

C o n s t r a i n t s t o P o l y c u l t u r eJohn E. Bardach

Environmentand PolicyInstitute. East-West Center, Honolulu,Hawaii, USA

A B S T R A C TP a t te r n s o f r e a r in g s e ve r a l c o m p a t i b l e a q u a t i c f o o d s p e c ie s t o g e th e r( p o l yc u l tu r e ) i n f r e s h , b r a c k i s h a n d s a l t w a t e r a r e d is c u s se d . E m p h a s i si s o n t e c h n o lo g i e s t h a t s e iz e o n c o m p a t i b il i ti e s o f th e o r g a n i s m s f o rs p a t i a l a n d ~ o r t e m p o r a l c o h a b i t a t i o n a n d o n a d a p t a t i o n t o d i f f e r e n tm a r k e t s. I n .f r es h w a te r, u s e o f a v i a n o r m a m m a l i a n s t o c k i s i n c h M e d .C o n s t r a i n t s d i sc u s s e d c o m p r i s e w a t e r q u a l i ty a n d q u a n t i t y a s w e l l a ss o m e a s p e c ts o f t e c h n i c a l i n fr a st ru c tu r e . A l s o , p r e s e n t l a n d a n d w a t e rm a n a g e m e n t c o n d i t io n s i n tr o p ic a l A s i a w h e n c e m o s t e x a m p l e s a r et a k e n , e x c e p t f o r J a p a n , s u g g e s t t h a t b e s t g a i n s c a n b e m a d e n o t b yc r e a ti n g n e w i n s t a l l a t i o n s b u t b y u p g r a d i n g e x i s ti n g o n e s t h r o u g h l ar ges c a le e s t a b l is h m e n t o f h a t c h e r ie s a n d t h r o u g h t h e i m p r o v e m e n t o fm a n a g e m e n t s k i l l s .

INTRODUCTIONBetween 1976 and 1981 the tonnage produced by animal aquacultureincreased by nearly 30%. If seaweed aquaculture were included thisfigure would rise to 40%. In contrast capture fisheries production forhuman consumption only rose by c i r c a 5% (Table 1). These trendscontinue, with gains in aquaculture outstripping those in fisheries.There are many variants of aquaculture pursued in fresh, brackish andsalt water, at many levels of intensity. It is the aquatic animal husban-dry of the semi-intensive kind, prominently using techniques of poly-culture, which offers the most substantial promise. Some of theconstraints to its development will be examined here.

In some kinds of aquaculture the water serves merely as support forthe animals that are grown in it, while in others various biological pro-287Aquacul tural Engineer ing 0144-8609/86/S03.50-- Elsevier Applied SciencePublishers Ltd, England, 1986. Printed in Great Britain


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288 J . E . B a r d a c hT A B L E 1Five Year Com parison of Production and G rowth o f Fisheries and Aquaculture"

1976 1981 % Ga in

Fisheries(edible produc ts) 50-1 52.6 4.9Aquaculture(Fish, crustace ans and m ollusks 5-05 6.51 28-9for human consump tion)Algae included 6.2 8.7 40.3"Based o n FAO ( 1976 -81), FAO (197 6), and Pillay (in press).

c e ss e s b a se d o n p h y s i c a l a n d c h e m i c a l p r o p e r t i e s o f th e m e d i u m a r es t e e r e d t o b e a n i n te g r a l p a r t o f th e p r o d u c t i o n p r o c e s s . T h e f ir st k i n di s f e e d l o t a q u a c u l t u r e w h i c h b e n e f i t s s u b s t a n t i a l l y f r o m t h e m o s tc o p i o u s p o s s i b l e w a t e r s u p p l y . T h e c h e a p e r t h i s s u p p l y , t h e m o r e i tc a n b e s i m p l y th r o w n a w a y a f te r s e rv i n g as s u p p o r t , a s c o n v e y o r o fo x y g e n a n d a s a c o n t i n u o u s f lo w ' f lu s h - to i le t ', c a r r y i n g a w a y m e t a b o l i cw a s t es . S n a k e R i v e r r a i n b o w t r o u t c u l t u r e a n d n e t c u l t u r e o f s e v e r a ls p e c ie s o f m a r i n e f i sh a r e g o o d e x a m p l e s . W h e n w a t e r o r la n d c o st sr is e, o r w h e n w a t e r e x c h a n g e p o s e s t e c h n i c a l p r o b l e m s , v a r i o u s e n g in -e e r i n g s o l u t i o n s a r e s o u g h t t o e n h a n c e w a t e r q u a l i t y ; t h e y c a n r a n g ef r o m s t ir r in g t o t h e i n j e c ti o n o f o x y g e n o r e v e n r e c y c l in g w i t h c o m p l e xf i l t e r s . A r e c e n t e x a m p l e w o u l d b e t h e u s e o f w i n d g e n e r a t o r s t oo b t a i n o x y g e n f r o m t h e d i s s o c i a t i o n o f w a te r , w i t h t h e r e su l ti n g h y d r o -g e n r e d u c i n g t h e p o w e r n e e d s f o r o x y g e n a t i o n . O t h e r d e v ic e s a r es e n s o r p r o b e s f o r d i s s o l v e d o x y g e n a n d n o z z l e s t o s u p p l y t h e g a s i nc o n j u n c t i o n w i t h c o m p u t e r i z e d f e e d i n g d e v i c e s f o r c a t f i s h . A l l t h e s ea r e c h a l l e n g e s t o e n g i n e e r i n g s k ills a n d i n g e n u i t y a n d t h e y m a y b ee c o n o m i c a l u n d e r c e r t a i n c i r c u m s t a n c e s , b u t t h e y a l s o p o s e t h e q u e s -t i o n o f h o w t o a t t a i n o p t i m a l u s e o f w h a t t h r e a t e n s t o b e a n i n c r e a s -i n gl y s c a r c e r e s o u r c e , n a m e l y c l e a n w a te r .

F e e d l o t m o n o c u l t u r e h a s p r o d u c e d g r e at q u a n ti ti e s o f an i m a l f le shp e r u n i t h o l d i n g s p a c e a n d its t o o l s a r e l a r g e ly o f t h e e n g i n e e r i n g k i n dw h i l e its l im i t a ti o n s a n d c o n s t r a i n t s h a v e b e e n l ar g e ly e c o n o m i c . T h eo t h e r a v e n u e t o a q u a c u l t u r e , t h a t o f st e e r in g b i o l o g i c al p r o c e s s e s i nt h e w a t e r t o f u r n i s h a l l o r m o s t o f t h e s u s t e n a n c e o f t h e c u l t i v a r s a n da ls o s u p p l y i n g r e s p e c t a b l e h a r v e s t s p e r u n i t a r e a o r v o l u m e , h a s b e e n


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C o n s t r a i n t s t o p o l y c u l t u r e 2 S 9

t h r o u g h p o l y c u l t u r e . M o s t s i m p l y p u t , p o l y c u l t u r e a t t e m p t s t o r e a rt o g e t h e r a n u m b e r o f s p ec i es t h a t a re c o m p a t i b l e w i th o n e a n o t h e r a n dt h a t m a k e u s e o f v a r i o u s f e e d i n g l e v e l s a n d n i c h e s , u su a l ly i n a p o n d ;p r o d u c t i o n m a y b e e n h a n c e d b y e x t r a n e o u s f e e d i n g . I t s t o o l s , a s i d ef r o m s o m e m e c h a n i c a l o r e n g i n e e r i n g d e v i c e s, a r e l a r g el y e c o - t e c h n i -c a l o r r e l a t e d t o t h e c u lt iv a r s t h e m s e l v e s a n d t h e f o o d o r g a n i s m s w i thw h i c h t h e y s h a r e t h e i r g r o w i n g sp a c e s . I n o t h e r w o r d s , t h e q u e s t is toa t ta i n a m a x i m u m o f th e e c o n o m i c a l l y u s a b le o v e r t h e e c o l o g ic a ll yn e c e s s a r y b i o m a s s . S u c h m a n a g e m e n t t e c h n i q u e s w i l l h a v e t o b eb a s e d o n u n d e r s t a n d i n g t h e r e l a ti o n s o f t h e m e t a b o l i s m o f all le v e ls int h e fo o d c h a i n , p r o m i n e n t l y i n c l u d i n g t h a t o f th e b o t t o m ( o r m u d )w a t e r i n t e r fa c e , a n d o f c o u r s e o n a t t e n t i o n t o w a t e r q u a li ty .

T o d o t h is i t w i ll b e n e c e s s a r y t o r e t a i n o r s e c u r e s m a l l d i u r n a l f lu c -t u a ti o n s i n 0 2 l ev e ls t h r o u g h b a l a n c i n g p h o t o s y n t h e s i s a n d r e s p i ra t io nb y a v o i d i n g s tr a ti fi c a ti o n a n d e x t e n d i n g t h e d e p t h o f th e p h o t i c z o n e .It a ls o m e a n s b a l a n c i n g p r o m i n e n t c a r b o n a n d n i t r o g e n s o u rc e s ,m a i n l y t h r o u g h e n h a n c i n g t h e ir r e c y c l i n g o r r e -u s e . U n f o r t u n a t e ly ,k n o w l e d g e o f m a n y o f t h e s e p r o c e s s e s s till e l u d e s u s a n d p o l y c u l tu r ep r a c t i c e s t h e r e f o r e m o s t l y t e n d t o b e t h o s e o f a t r a d e o r c r a f t r a t h e rt h a n b e i n g b a s e d o n w e l l e s t a b l is h e d a p p l i e d s c i e n c e m e t h o d s . I n th ef o l l o w i n g p a g e s I w i ll e x a m i n e e x a m p l e s o f p o l y c u l t u r e w i t h a v ie w t or e d u c i n g u n c e r t a i n t i e s a n d / o r e n h a n c i n g r e l i a b i l i t y o f p o l y c u l t u r em a n a g e m e n t m e t h o d s . S i n c e a q u a c u l t u r e i s a b u s i n e s s , I w o u l d a l s od e a l w i t h s o m e e c o n o m i c a s p e c t s o f p o l y c u l t u r e ; a l l t h e s e w i l l , o fc o u r s e , r e l a t e t o c o n s t r a i n t s o f o n e s o r t o r a n o t h e r .

P O L Y C U L T U R E P A T T E R N ST h e f ir st e x a m p l e o f t h e s e p a t t e r n s is f r o m I n d i a ( T a b le s 2 a n d 3 ). I nt hi s sy s t e m I n d i a n c a r p w e r e g r o w n t o g e t h e r w i t h C h i n e s e c a r p , w i thn u t r i e n t i n p u t s b e i n g p r o v i d e d b y d u c k s , p a r t l y g r o w n o n t h e p o n d s ,a n d b y p l an t s, g r o w n o n t h e b e r m s a n d f e d t o t h e g ra ss c a r p ( J h in g r a na n d S h a r m a , 1 9 8 0 ) . N o t e t h a t t h e f e r t i l i z e r i n p u t b y t h e b i r d s i s n o ta c c o u n t e d f o r b u t th a t t h e b i rd o p e r a t i o n b r o k e e v e n ( T a b le 3 ).

S ix s p e c i e s w e r e g r o w n i n a n a t t e m p t t o fil l a s m a n y f e e d i n g n i c h e sa s p o s s i b l e , w i t h e m p h a s i s o n f i s h t h a t f e e d i n t h e w a t e r c o l u m n .A m o n g t h e s e m r i g a l a n d r o h u a r e m o r e a p p r e c i a t e d t h a n t h e r e s t , b u tt h e y w e r e a ll g iv e n e q u a l w e i g h t i n th e a c c o u n t i n g s i n c e th e y w e r e s o l d


4/14

TABLE2

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WeB

naUsna11h

PmdSo

Wiha~kao9

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81

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35

96

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1

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4

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7

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1

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6

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9

5

1

6

9

3

1

1

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1

1

5

1

1

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78

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51

25

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oumnIv=1cbvcOnmiv=Omnve


5/14

Constra in ts to po lyc u lm re 291t o a g o v e r n m e n t d i s t r i b u t i o n s c h e m e t h a t d i d n o t d i f f e r e n t i a t eb e t w e e n t h e v a l u e s o f t h e d i f f e r e n t s p ec i es .

U n d e r d i f f e r e n t c o n d i t i o n s o f f is h p o l y c u l t u r e , s u c h a s in C h i n a ,s t o c k i n g i s a d j u s t e d t o a c c o u n t f o r m a r k e t p r e f e r e n c e s ; n e a r H o n gK o n g b i g h e a d c a r p a r e f a v o r e d o v e r s il v er c a r p t h o u g h f e w e r o f t h ef o r m e r c a n b e g r o w n i n e q u i v a l e n t p o n d s . A l s o , w h e r e g r a s s c a r p a r ef a v o r e d , a s t h e y a r e i n t h e Y a n g t s e D e l t a , t h e p ig m a n u r e w h i c h is u s e da s f e rt il iz e r is p l a c e d o n t h e b a n k s a n d m a n u r e m a y o r m a y n o t a ls o b ea d d e d t o t h e p o n d s . T h i s p r o d u c e s m o r e g r a ss c a r p t h a n s il ve r c a r p , ar e s u l t t h a t i s o f i n t e r e s t i n v i e w o f t h e d e v e l o p m e n t o f C h i n a ' s f r e ef o o d m a r k e t s . G r o w - o u t t im e is n i n e m o n t h s t o o n e y e a r, s i n ce a f is hf o r t h e m a r k e t m u s t w e i g h s e v e r a l h u n d r e d g r a m s . A l t o g e t h e r t h e r em a y b e a s m a n y a s n i n e s p e c i e s i n C h i n e s e p o l y c u l t u r e , a n d t h es c h e m e s a r e a ll g e a r e d t o m a x i m i z e n u t r i e n t r e c y c li n g a n d u s e m a n u r ea n d p l a n t m a t t e r . T e n t o n n e s h a - ~ a r e n o t r a r e a n d t h i r te e n h a v e b e e na c h i e v e d ( Z w e i g , 1 9 8 4 ).

A s f o r t h e o t h e r i n p u t s , t h e ' M a h u a ' c a k e ( T a b l e 3 ) s e r v e s f o r s a n i -t a ti o n o f t h e p o n d b o t t o m f r o m w h i c h f e rt il e m u d is a ls o r e m o v e d a n du s e d a s c o m p o s t , a f t e r h a r v e s t ; n o e x t r a n e o u s f e e d i s p u r c h a s e d .L a b o r a l s o i n c l u d e s a e r a t i o n ; t h e d e v i c e s a r e n o t d e s c r i b e d , n o r i s t h es c h e d u l e o f t h e o p e r a t i o n . R e m e m b e r i n g t h e c r af t a s p e c ts o f p o ly -c u l t u r e m a n a g e m e n t , w e s h o u l d n o t e , h o w e v e r , t h a t C h i n e s e p o l y -c u l t u r i s ts u s e v a r i ous s i gns a n d s i gna l s t o a c t i va t e s ti r ri ng : gu l p i ng i s, o fc o u r s e , a l r e a d y a d i st r e s s s ig n f o r w h i c h o n e h a r d l y w a i ts , b u t o r i e n t a -t io n o f t h e f i sh w i t h r e g a r d t o t h e d i r e c t i o n o f t h e w i n d o r t h e i r r e l u c -t a n c e t o s o u n d w h e n f r i g h t e n e d a r e e a r l i e r s ig n a l s o f o x y g e n l ac k ;w h e n t h e s e a r e o b s e r v e d , t h e p o n d s a r e s t i r r e d o r s p r a y e d ( Z w e i g ,1984 ) .

T h e s e p o l y c u l tu r e e x a m p l e s w e r e t a k e n f r o m n a t io n s w h e r e l a b o r isr e l at iv e l y c h e a p a n d t h e s ta t e o f t e c h n i c a l i n f r a s t r u c t u r e m i g h t m i ti g a tea g a in s t t h e u s e o f m u c h m a c h i n e r y o r a u t o m a t i o n . A l s o , p o n d l a y -o u tis h a r d l y s t a n d a r d i z e d a n d o f t e n t h e f a rm s a r e s m a ll e n o u g h f o r f am i lyl a b o r to w i n o u t o v e r m e c h a n i c a l d e v i ce s w h i c h sa v e m a n u a l w o r k .Q u e s t i o n s n e v e r t h e l e s s e x is t a b o u t t h e b e s t u se s o f p o n d e c o l o g y a n da b o u t t h e d e si g n a n d u s e o f s o m e m e c h a n i c a l d ev i c es .T h e n e x t e x a m p l e is f r o m p o n d o p e r a t io n s o f A q u a t ic F a r m s L t d inO a h u , H a w a i i , w h e r e s h r i m p a r e g r o w n a s t he p r i m a r y c r o p t o g e th e rw i t h t i l a p i a a n d o y s t e r s . I n c o n t r a s t t o g r o w i n g o n l y f i s h , p o l y c u l t u r ew i th c r u s t a c e a n s o b v i o u s l y p r e c l u d e s h a v i n g p i s c in e u s e r s o f th e


6/14

TABLE3

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8/14

294 Z E. Bardach

bottom, whether for feeding or breeding. In consequence, the hybridmale tilapia (crosses of Oreochromis mossambict~s and ni lot icus)which are using the plankton of the water column are kept in cages forthe seven to nine months it takes to grow them from fingerling (circa10 g) to market sizes (circa 450 g). The cages are very simple con-structs of plastic-covered wire mesh; they are arranged in rows andthey can be moved from pond to pond when the three times yearlyharvest of shrimp has to be undertaken. The shrimp P ene t t s vannam e iare grown to a weight of about 15 g, the smallest acceptable size forthe trade, to optimize on the rapid growth phase of juvenile animals.The oysters, reared for a selective half shell trade, are kept in flumesand bathed in pond effluents that pass relatively rapidly over them.Water from the flumes, enriched by oyster pseudofeces, may bere-cycled to various degrees.

So much for a description of the pond farming operation, withhatcheries for fish and shrimp not being mentioned. Managementrequires first a balancing of salinity to around 15%o achieved bymixing water from a freshwater stream with that pumped from a saltwater well; in essence, only evaporation is replaced. This salinity levelfavors phytoplankton growth in which desirable diatoms predominate;it may also present an osmotic optimum, at least for the shrimp. Bothfish and shrimp are fed with high protein broiler chicken starter rationat decreasing levels in percentage of body weight; the shrimp, forinstance, receive 10% at stocking and 2% before harvest. The pondsalso receive doses of urea and phosphoric acid. Feed levels aremoderate, compared to feedlot culture, with much reliance on plank-tonic carbon fixation in which a preponderance of diatoms over greenand blue-green algae is desired; Chinese polyculturists also strive for adominance of diatoms, liking 'fresh brown' water color which indi-cates such a plankton composition. Diatom preponderance, inciden-tally, is more difficult to achieve in fresh than in brackish water. Pondperformance is ascertained by weekly sampling of the shrimp andfeeding is adjusted accordingly. At the time of the trimestral shrimpharvest the ponds are dried and pond bottoms may be raked or roto-tilled; some material may be discarded after a one year build-up.It was attempted to grow oysters in the pond instead of raising them'after' the ponds, but apart from inconvenience of handling it appearsthat oysters fare better when water with their plankton food in it ispassed over them, as it is in their prime natural habitats, the tidal


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296 J. E. BardachTABLE 4Thirty-five Comm only M arketable M arine W ild Crops Th at Ap pear to be Farmable

in the Reef o r M angal Environ m ent on a Diversified Reef Fa rm (quite clearly no onesite would be suitable for all in this list and man y more organisms could be adde d)"Arthropods Coelenterates Echinoderms

Mangrove crabsPenaeid shrimps Ac roporo id coralsAlcyonarian coralsPrecious coralsSea fansBlack corals

Sea urchinsStarfishesTrepang holothurians

Mollusks Seaweeds VertebratesAnadara Caulerpa Aquarium speciesCardium Digenia Dragons/lizardsMussels Eucheurna FishesOther clams Gracilaria GroupersOysters Halymenia KyphosusPearl oysters Hormophysa Sea horsesTridacnids Monostroma Sea snakes

Sargassum SiganidsTurbinaria Turtles"Based on Doty(1981).f lo r a a n d f a u n a a r o u n d t h e m . P r o p e r a t t e n t i o n t o ex t e r n al i ti e s is a sn e c e s s a r y h e r e a s i t i s i n f r e s h a n d b r a c k i s h w a t e r p o n d s a n d m a n a g e -m e n t , e x t e n d i n g o v e r m a n y k i l o m e t e r s o f c o a s t li n e , re s t s o n l a rg e rs c a l e c o o p e r a t i o n t h a n i s c u s t o m a r y i n f i s h e r i e s a n d f o r t h a t m a t t e r i na q u a c u l t u r e ( O c e a n R e s e a r c h I n s t i t u t e , 1 9 8 4 ; T a b l e 5). E v e n t u a l l yy ie ld s o f 2 - 4 m i l l io n t o n n e s ( M M T / a r e a n t i c i p a t e d f r o m t hi s k i n d o fm a r i n e p o l y c u l t u r e a l o n g t h e c o a s ts o f J a p a n .

D I S C U S S I O N A N D C O N C L U S I O NA s t h e s e e x a m p l e s p o i n t t o p o s s i b i l i t i e s o f u p g r a d i n g o f a q u a c u l t u r ep r a c t i c e s t h e y i n v i t e b r o a d q u e s t i o n s o f s i t e a n d w a t e r a v a i l a b i l i t y . I nt h e c a s e o f t h e f r e s h w a t e r s y s t e m , f o r m e r r e la t iv e l y p r i s t in e e s t u a r i e sa n d s e a s o n a l l y i n u n d a t e d a r e a s o f t h e w o r l d ' s l a r g e r r i v e r s y s t e m sw h i c h s u p p l i e d l a r g e f i s h t o n n a g e f r o m w i l d h a r v e s t s a r e v i r t u a l l y


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Constraints to polyculture 2 97T A B L E 5Ex plora t i o n o f M e thod s fo r Enhan c ing t he A qua t i c Po t en t i a l o f Shi ji ki Bay and O ther

Loc a t i ons i n Wes t e rn Ky ushu , iBased on O cea n R esea rch Ins ti tu t e , 1984) .,4. Com prehensive & Fu nd am en tal Studies o f the Shi f ik i Bay Cornmuni~ ' L aying Stresson the Ec o lo~ ' o f Re d Sea Bream Larvae

Goal s :O p e n c le a n b ayH i g h p r im a r y p r o d u c t i o nEf f i c i en t t u rno ver o f ma te r i a l s i n food cha in a ro und f ish she l te r s on sea b o t t omHea l thy , f e rt il e nur se ry g roun dF l e x ib l e s t r u c tu r e o f c o m m u n i t yCar ry ing c apac i t y t o be fu l l y exp lo i t edStudies in Progress :L i fe h is t o ry a n d p r o d u c t i o n o f p l a n k t o n a n d b e n t h o sE n e r g y f l o w t h r o u g h t h e s h e l te r f o o d c h a i nCar ry ing capac i t y o f r ed sea b ream, aba lone and sea u rch inT u r n o v e r p r o c e s s o f d e t r it u s a r o u n d s e a b o t t o mCo m m uni ty s t ruc tu re o f beach l ay ing s tr e s s on f l ound erW a t e r e x c h a n g e p r o c e s sP rod uc t ion o f sea weed and sea g ras sM ec hani sms o f annua l f l uc tua t ions o f O-age r ed sea b ream dens i tyRole o f r ee f fo r b io log i ca l p ro duc t ion

B. ~. \rploration Projects in M arine Culture and M an ag em en tM ar ine r anch ing pro j ec t ( r ed sea b ream , f l ounder , aba lone , s ea u rch in , e tc .)Biom ass proje ct (sea weed and grass)Ar rang e an d ex ploi ta t io n of coas t f ishing gro un d p roject (ar ti ficial reef , enha ncingn u r s e r y g r o u n d )

Collaborating OrganizationsFi she rm an ' s Un ion o f Sh iji kiAquacu l tu re Resea rch Labora to r2 ,' of NagasakiF a r S ea s F i sh e r ie s R e s e a r c h L a b o r a t o r yT o h o k u R e g. F i s h e ri e s R e s e a r c h L a b o r a t o r yNagasak i Unive r s i t y Facu l ty o f Ed uca t i onNagasaki Un ivers i ty Facul ty of F isher iesKy oto U nive r s i ty Facu l ty o f Agr i cu l t u reO c e a n R e s e a r c h I n s ti tu t e o f T o k y o U n i v e r si ty


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298 J . E . B a r d a c h

g o n e ; i r r i g a t io n a g r i c u l t u r e a n d t h e u s e o f p e s t i c i d e s a n d f e r t i li z e r h a v ec h a n g e d t h e c o m p l e x i o n o f t h e e n v i r o n m e n t i n l o w l a n d t r o p i c a lr e a c h e s , i n c l u d i n g th e d i m i n u t i o n o f w i l d s to c k t o s u p p l y s e e d f o rp o n d o p e r a t i o n s . H e n c e t h e r e n e e d t o b e su f fi c ie n t h a t c h e r i e s tos u p p l y t h e f r y a n d s u f fi c ie n t i n d i g e n o u s k n o w l e d g e t o r e a r t h e m .W h e r e t h e f i s h t o b e s t o c k e d c a m e f r o m n a t u r a l w a t e r s s u c h k n o w -l e d g e is u s u a ll y l a c k in g . A l s o n e e d e d is a m o r e e c o l o g i c a l l y s o u n dc o n c e r n f o r w a t e r q u a l i t y f o r a q u a c u l t u r e , a s it c a n b e a f f e c t e d b y a g ri -c u l tu r a l, d o m e s t i c a n d i n d u s t ri a l p o l lu t i o n . E x a m p l e s a r e l e g i o n i nA s i a , w h e r e s u c h e x t e r n a l i t i e s h a v e c o n s t r a i n e d t h e u p g r a d i n g f r o me x t e n s i v e to s e m i - in t e n s i v e p o l y c u l t u re . O f t e n t h e c r u x o f t h e m a t t e r i sl a c k o f c o m m u n i c a t i o n a m o n g a g e n c i e s a n d l a c k o f m e a n s t o b r i n ga b o u t n e c e s s a r y c h a n g e s t h a t a re a c c e p t a b l e f r o m t h e v a n ta g e p o i n t o fr e a s o n a b l e t ra d e -o ff s. T h e c o m m u n i c a t i o n a n d c o o p e r a t i o n s h o w n int h e J a p a n e s e c o a s ta l p o l y c u l t u r e m e n t i o n e d e a r li e r is a n e x c e p t i o nr a t h e r t h a n t h e r u l e.

W at e r ava i l ab i li ty , an d a l s o t o a g r ea t ex t en t w a t e r qua l i ty , a r e no t s os e r i o u s f o r b r a c k i s h w a t e r p o l y c u l t u r e ; a f te r a ll t h e r e a r e i n S o u t h e a s tA s i a a l o n e a r o u n d 3 .7 m i l l i o n h e c t a r e s o f m a n g r o v e s w a m p s o u t o fw h i c h o n e c o u l d c a r v e l a rg e fa r m s ( K n o x a n d M i y a b a ra , 1 9 8 4 ). S u c h as u p e r f i c i a l a n d s i m p l i s t i c s t a t e m e n t h a s m i s l e d p o l i t i c i a n s a n d i n t e r -n a t i o n a l a g e n c i e s , s i n c e it d o e s n o t c o n s i d e r t h a t a l a r g e p e r c e n t a g e o ft h e s e a r e a s m u s t b e r u l e d o u t f o r a q u a c u l t u r e , i n p a r t b e c a u s e o fa c c e ss a n d i n f ra s t ru c t u r e d e f i c ie n c i e s , b u t m o r e i m p o r t a n t ly b e c a u s et h e y a r e t h e b a si s f o r t h e p r e s e r v a t i o n o f w i l d st o c k s o n w h i c h s h r i m pa n d i m p o r t a n t f in f is h c a p t u r e f i s h e r i e s r ely . B u t e v e n w h e r e c o n d i t i o n sa r e f a v o r a b l e f o r t r a n s f o r m a t i o n o f m a n g r o v e a r ea s i n to p o n d s t h e r e iss ti ll i n a d e q u a t e k n o w l e d g e o f h o w t o d o t hi s in a n e c o l o g ic a l ly s o u n dm a n n e r ; p e r t i n e n t r e s e a r c h i s t h e r e f o r e d e s i r a b le .

H o w e v e r , t h e r e a r e , e s p e c i a l l y i n t r o p i c a l A s i a , m a n y t e n s o f t h o u -s a n d s o f h e c ta r e s o f b r a c k i s h w a t e r p o n d s w i t h th e i r c a n a ls t h a t n o wp r o d u c e l o w y i e ld s o f s h r i m p a n d fis h. T h e s e c o u l d b e u p g r a d e d f orl es s m o n e y t h a n it w o u l d t a k e t o b u i ld n e w o n e s ; h a t c h e r i e s c o u l d b ee s t a b l i s h e d t o s e r v i c e t h e m , f e e d m i l l s c o u l d b e c h a l l e n g e d t o f u r n i sha f fo r d a b le f ee d s , a n d m a n a g e m e n t m e t h o d s c o u l d b e m o d e r n i z e d . As e v e r a l -f o l d i n c r e a s e i n a n i m a l p r o t e i n p r o d u c t i o n c o u n t r y - o r r e g io n -w i d e w o u l d r e s u l t , i f , i n a d d i t i o n , c r e d i t s c h e m e s c o u l d b e i n s t i t u t e dt h a t a s s u r e b e n e f i t s to f a r m e r s r a t h e r t h a n t o a g e n ts , a n d i f t r a in i n ga n d e x t e n s i o n i n n o v a t i o n s c o u l d b e s e t u p t h a t le a d t o w i d e i n tr o d u c -


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Constraints to polycu#ure 299t i o n o f t h e b e s t p r e s e n t l y k n o w n p o l y c u l t u r a l p r a c t i c e s . A t t e n t i o n t ot h e s e e x ig e n c ie s b y f u n d i n g a n d a p p r o p r i a t e g o v e r n m e n t a g e n c ie sw o u l d r a i s e a q u a c u l t u r e y i e l d s f a s t e r t h a n s t a r t in g n e w l a r g e s c a lea q u a c u l t u r e d e v e l o p m e n t s a n d it w o u l d d o s o i n a s o ci a ll y h i g h lya c c e p t a b l e m a n n e r ; t h e o p e n i n g o f l a rg e n e w t r a c ts m a y s t il l b e p u r -s u e d , b u t m o s t l y w i t h a v i e w t o a m o r e d i s t a n t f u t u re . I t g i v e s m e s a ti s-f a c t i o n i n d e e d t h a t w h a t I s a id h e r e h a s a l so b e e n t h e t e n e t , i n p a r t , o ft h e i n a u g u ra l a d d r e s s o f th e n e w p r e s i d e n t o f t h e W o r ld M a r i c u lt u r eS o c i e t y , D r E d w a r d S c u r a . W i t h h i m I d r a w a t t e n t i o n t o b r o a d l ya p p l i c a b l e c o n s t r a i n t s t o p o l y c u l t u r e t h a t l i e i n t h e l a c k o f a t t e n t i o n t os o c i a l , e c o l o g i c a l a n d e c o n o m i c s y s t e m s t h i n k i n g w h e n i t c o m e s t oa q u a c u l t u r e p l a n n i n g o n a n a t i o n a l s c al e.

L e a v i n g t h e m a c r o - a n d g o i n g to m e s o - a n d m o r e m i c r o - c o n s i d e r a -t io n s , w h i l e s ti ll d r a w i n g o n i m p l i c a t i o n s o f th e e x a m p l e s D v e n e a r li e r,it a p p e a r s t h a t u p g r a d i n g o f p o l y c u l t u r e o n t h e f a r m l e v e l r e q u i r e sb o t h a m o r e t h o r o u g h i n f o r m a t i o n b as e a n d m a n a g e r s a n d o p e r a t o rsw h o k n o w n o t o n l y w h a t to d o b u t a ls o w h y th e y w o u l d p e r f o r m s u c hm e a s u r e s . T h i s i s e a s i e r s a i d t h a n d o n e b e c a u s e s e v e r a l a s p e c t s o fp o n d s y s t e m s r e l a t i o n s a r e s t i l l o n l y p a r t l y k n o w n . P a t t e r n s o fm a t e r ia l s fl o w s s u c h a s m a y b e e l u c i d a t e d b y u s in g la b e l e d c a r b o n a n dl abe l ed n i t r ogen a r e ca s e s i n po i n t , a s i s a l ga l , e s pec i a l l y d i a t om,e c o l o g y . A l s o t h e r e is i n m a n y i n s t a n c e s i n s u f fi c i e n t r e l a t i o n b e t w e e nr e s e a r c h a n d p r a c t ic e , p o t e n t i a l ly l e a d i n g to d e f i c i e n c i e s i n c o n c e p ta n d o i - g a n iz a t io n o f t ra i n i n g a n d e x t e n s i o n p r a c t i c e s .O n t h e s o c i o - e c o n o m i c 'f ro n t ', u p g r a d i n g t h e s iz e s o f h o ld i n g sw o u l d i n f l u e n c e te c h n i c a l a s w e l l a s c r e d i t m e a s u r e s . T h e r e l a t i o n o ft h e s e in p u t s t o f a rm s t r u c t u r e a n d f u n c t i o n h a s h a r d l y b e e n s t u d i e d . Inf ac t in th e n a t i o n s w h e r e u p g r a d i n g m e a s u r e s w o u l d p a y o f f t h e r e a r ef ew e x p e r ts w h o c o u l d a d d r e s s t h e m s e l v e s to s u c h q u e s t io n s , a n dexpa t r i a t e s w i t h t he r equ i s i t e s k i l l s a l l t oo o f t en l ack l oca l know l edgea n d i n si g h t. I b e l i e v e t h a t a t t e n t i o n t o t h is a s p e c t o f i m p r o v i n g p o l y -c u l t u r e i n v a r io u s n a t i o n s i s a s, if n o t m o r e , i m p o r t a n t t h a n a t t e n t i o n t ot he t ech n i ca l s ide .

A C K N O W L E D G M E N T SI g r a t ef u l ly a c k n o w l e d g e i n p u t s f r o m d i s c u s s i o n s w i t h D r R . Z w e i g , D rE . S c u r a , D r R . M c L a r n e y , P r o f e s s o r M . D o r y a n d M r A . M . K u l ji s.


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D oty, M . ( 1981 ). The Diversified Farming o f Coral Reefs. U niversity o f HawaiiH.L. Lyon s Arb ore tum Lecture No. II , U niversi ty of Haw aii Press, H aw aii ,29 pp.FAO (1976-81). Fisheries Stat ist ics, FAO Yearbooks of Fishery Stat ist ics,Ca t ches and Landings .FAO (1976). Fisher ies Re po rt 188, Rep ort of the FA O Technical Conferenceon Aqua culture, K yot o , J a pa n , 26 M a y- 2 J une 1976 .Jhingran, V. G. & Sharm a, B. K. (1980) . Integra ted l ives tock-f i sh fa rming inIndia, In: Integrated Agrictdture-Aq,Laculmre Farming Systems, IC L~ R MConference Proce edings No. 4, eds R. S. V. Pul l in & Z. H. Shehadeh,M anil a. pp . 13 5-42 .Kno x, G. A. & M iyabara , T . (1984) . Coastal Zo ne Resource Development andConservation in Southeast Asia. Doc . No. ISBN 92-3-102250-4 ,U N E S C O / J a ka r t a , 182 pp .Ocean Research Ins t i tute , Univers i ty of Tokyo (1984) . Exploration ofme thod s fo r enhancing the aquatic potential o f Shijiki Bay. M imeo, 6 pp .Pillay, T. V. R. (in p ress). Proc. W orm Aqu aculture Conf., Venice, 1981.Zweig, R. D. (1984). China 's prol i f ic f ishponds. C E R E S 100 , F A O , R om e ,pp . 22-6 .

Bardach 1986 Aquacultural-Engineering

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