Boyd 1986 Aquacultural-Engineering

7/28/2019 Boyd 1986 Aquacultural-Engineering

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Aq uacu l tural Engineer ing 5 1 9 8 6) 1 3 5 - 1 4 6

C o m m e n t s o n t h e D e v e l o p m e n t o f T e c h n iq u e s fo rM an a ge m e n t o f E n v i r on m e n t a l Q u a l it y in A q u ac u l t u r eC l a u d e E . B o y d

D e p a r t m e n t o f F i s h e ri e s a n d A l l i e d A q u a c u l t u r e s , A l a b a m a A g r i c u lt u r a l E x p e r i m e n tS t a ti o n, A u b u r n U n i v er s it y , A l a b a m a 3 6 8 4 9 , U S A

A B S T R A C TM a n a g e m e n t p r o c e d u re s w h i c h i m p r o v e o r s ta b i li ze e n v i r o n m e n t a lq u a l i t y in a q u a c u l t u r e p o n d s a r e n e e d e d . T h e d e v e l o p . t e n t of" s u c hp r o c e d u r e s r e q u i re s k n o w l e d g e o f q u a n t it a t iv e r e l a ti o n s h ip s a m o n g t w os e t s o f v a ria b le s: ( I ) f i s h p r o d u c t i o n a t t d s p e c if ic a s p e c t s o f e n v i r o n -m e n t a l q u a l it y a rt d (2 ) t h e m a n a g e m e n t p r o c e d u r e a n d e n v i r o n m e n t a lq u a l i o t T h e s p e c if ic c h a n g e s d e s i re d i n e n v i r o n m e n t a l q u a l i ty m u s t b eiden t i f ied , an d the e f f ec t oJ 'a g iven degree o f ap p l i ca t ion oJ 'a mam~ge-. t e n t p r o c e d u r e o t l b o t h e n v i r o n m e n t a l q u a l i t y a n d a q u a c u l t u r a lp r o d u c t i o n m u s t b e a s ce r ta i n ed . M a n a g e m e n t p r o c e d u r e s m u s t p r o -du ce pred ic tab le r e su l t s a t a r eas 'onab le cost .

E n v i r o n m e n t a l f a c to r s w h i c h m u s t b e c o n s i d e r ed i n m a n a g i n g w a te rq u a l i O , i n f e r tU i z e d p o n d s a n d i n p o n d s i n w h i c h J O e & a r e a p p l i e d a r ed i sc u s se d . S o m e e x a m p l e s o f t h e d e v e l o p m e n t o f s u c c e ss f id e n v i ro n -m e n t a l q u a l it y m a n a g e m e n t t e ch n i q u e s a r e p r o v i d e d a n d t o p ic s f o rf i t tu r e r e s e a rc h a r e m e n t i o n e d .

I N T R O D U C T I O NT h e m o s t f u n d a m e n t a l a n d c o m p l e x a s p e c t o f a q u a cu lt u ra l e n g in e e r -i n g in v o l v e s t h e m a n a g e m e n t o f e n v i r o n m e n t a l q u a lit y , a n d t h e a b il i tyo f a m a n a g e r t o m a i n t a i n a h ig h q u a li ty e n v i r o n m e n t in a p o n d o f t e nd e t e r m i n e s t h e m a r g i n o f p r o fi t. M o s t w a t er q u a li ty m a n a g e m e n t t e c h -n i q u e s w e r e d e v e l o p e d t h r o u g h r e s e a r c h , or s o m e t i m e s b y tr ia l a n de r ro r , a t o n e o r a f e w l o c a t i o n s . B e c a u s e o f d i f f e r e n c e s i n e n v i r o n -m e n t a l c o n d i t i o n s a m o n g l o c a l i t i e s a n d a n i n c o m p l e t e k n o w l e d g e o f

13 5A q ua cu ltu ra l E n gin ee rin g 0 1 4 4 - 8 6 0 9 / 8 6 / S 0 3 . 5 0 - E lse v ie r A p p l i e d S c i e n c ePub l i shers Ltd , En glan d , 19 86 . Pr in ted in Gr eat Br i ta in


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136 C. E. Boydf a c to r s i n f l u e n c i n g r e s p o n s e , t h e b e n e f i ts o f a m a n a g e m e n t te c h n i q u em a y y a w g re a tly . F u r t h e r m o r e , m a n a g e m e n t p r o c e d u r e s s h o u l d b eb a s e d u p o n a s o u n d u n d e r s t a n d i n g o f c au s e a n d e ffe ct; b u t m a n y w e r ed e v e l o p e d f r o m u n t e s t e d h y p o t h e s e s . T h e u l t i m a t e g o a l o f e n v i r o n -m e n t a l r e s e a r c h i n a q u a c u l t u r e is t w o - f o l d : ( 1 ) t o d e v e l o p q u a n t i t a t i v em e t h o d s f o r p r e d i c t i n g t h e e f f e c t s o f f i s h c u l t u r e o n e n v i r o n m e n t a lq u a l i t y a n d v i c e v e r s a , a n d ( 2 ) t o d e v i s e m a n a g e m e n t p r o c e d u r e sw h i c h w i ll p r e d i c t a b l y i m p r o v e o r s ta b il iz e e n v i r o n m e n t a l q u al it y a t ar e a s o n a b l e c o s t .

I w i ll d i sc u s s r e s e a r c h o n m a n a g e m e n t o f e n v i r o n m e n t a l q u a l it y inf e r t i l i z e d p o n d s a n d i n p o n d s t o w h i c h f e e d s a r e a p p l i e d . I w i l ld e m o n s t r a t e t h e c o m p l e x i t y o f t h e s y s t e m s a n d t h e w i d e r a n g e o ff a c t o r s t h a t s h o u l d b e c o n s i d e r e d ; I w i l l a l so s h o w t h a t i t is p o s s ib l e t od e v e l o p r e l i a b l e m a n a g e m e n t p r o c e d u r e s . I n e s s e n c e , t h e d e v e l o p -m e n t o f a r e l i a b l e p r o c e d u r e r e q u i r e s a m o d e l o f t h e p r o c e s s e s i nq u e s t i o n , s o t h e a p p l i c a b i l it y o f s im u l a t i o n t e c h n i q u e s w i ll b e o b v i o u s .

F E R T I L I Z E D P O N D ST h e p o s it iv e c o r re l a t io n b e t w e e n p h y t o p l a n k t o n p r o d u c t iv i ty a n d f is hy i e l d i n p o n d s h a s b e e n d e m o n s t r a t e d m a n y t i m e s . I t i s a l s o w i d e l yr e c o g n i z e d t h a t t xv o n u t r i e n t s , p h o s p h o r u s , a n d n i t r o g e n t o a le s s e rd e g r e e , n o r m a l l y l i m i t p h y t o p l a n k t o n p r o d u c t i v i t y i n p o n d s . T h e r e -f o re , a p p l ic a t i o n s o f p h o s p h a t e a n d n i t r o g e n f e rt il iz e r s h a v e b e e n u s e dt o i n c r e a s e f i s h y i e l d s . R e s e a r c h a t s e v e r a l s t a t i o n s h a s d e m o n s t r a t e dt ha t fo r po nd s on a s t a t ion , a pa r t i cu l a r a pp l i ca t i o n r a t e o f a f e r t i li z e rw i ll r e s u l t in a p r e d i c t a b l e i n c r e a s e i n t h e y i e l d o f a g i v e n a q u a c u l t u r a ls p e c i e s. H o w e v e r , i n p r a c t i c e t h e y i e ld r e s p o n s e t o t h e f e r t il i z e r d o s e isn o t s o p r e d i c t a b l e b e c a u s e o f d i f f e re n c e s i n e n v i r o n m e n t a l c o n d i t io n sa n d a q u a c u l t u r a l s p e c i e s .B e l o w I w i ll d i s c u s s f a c t o rs t h a t i n f l u e n c e th e r e s p o n s e t o p o n d f e r-t il iz a t io n . T h e r e a r e p r o b a b l y m o r e f a c to r s t h a n g i v e n , a n d i n t e r -ac t i ons a r e a l s o l ike ly .Need f o r li m eF o r a p o n d t o r e s p o n d p r o p e r l y t o f e rt il iz a ti o n , t h e b o t t o m m u d s m u s tn o t b e h i g h l y a c i d i c a n d t h e w a t e r s h o u l d h a v e a t o ta l a l k a l in i t y a n d


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M an age m en t o/ e n vironrnental quali U in aquac,~ !uLre 13 7t o t a l h a r d n e s s o f 2 0 m g l i t e r - ~ o r m o r e a s C a C O ~ . A c i d i c m u d ss t ro n g l y a d s o r b p h o s p h a t e ; b e n t h i c o r g a n i s m s , i n c l u d i n g b a c t e ri a , d on o t g r o w w e ll a t lo w p H ; p h y t o p l a n k t o n d o n o t h a v e a d e q u a t e c a r b o na n d c a l c i u m f o r g r o w t h i n s o f t , w e a k l y a l k a l i n e w a t e r s . A c i d i c m u d sm a y b e n e u t r a l iz e d a n d a lk a l in i ty a n d h a r d n e s s o f w a t e r i n c r e a s e d b ya p p l i c a t i o n o f l i m i n g m a t e r i a l s . L i m i n g h a s m o r e t h a n d o u b l e d f i s hp r o d u c t i o n i n s o m e f e r ti li ze d p o n d s w i t h a c i d ic m u d s a n d w a t e r s o flow a lka l i n i t y .

T h e q u a n t i ty o f li m i n g m a t e r i a l r e q u i r e d p e r h e c t a r e w i ll v a r yg r e a tl y a m o n g p o n d s . T h e f o ll o w i n g d i s c u s s io n d e s c r i b e s a te c h n i q u ef o r c a lc u l a t i n g t h e l i m e r e q u i r e m e n t o f f is h p o n d s . It a l so d e m o n s t r a t e sh o w k n o w l e d g e o f b a s ic p r o c e s s e s i n p o n d s c a n b e u s e d i n d e v e l o p i n ga m a n a g e m e n t p r o c e d u r e .

B o y d ( 1 9 7 4 ) f o u n d t h a t t o ta l h a r d n e s s a n d t o ta l a l k a li n i ty o f p o n dw a t e r s e x c e e d e d 2 0 m g l it er -~ w h e n t h e b a s e u n s a t u r a t i o n o f m u d sw a s 0 " 2 o r l e s s . F u r t h e r m o r e , t h e r e w a s a s t r o n g c o r r e l a t i o n b e t w e e nt h e b a s e u n s a t u r a t i o n o f p o n d m u d s a n d t h e ir p H v a lu e s , a n d a m u dp H o f 6 c o r r e s p o n d e d t o a b a s e u n s a t u r a t io n o f 0 "2 . T h e r e f o r e , i f t h ep H o f a m u d is k n o w n , t h e b a s e u n s a t u r a t i o n c a n b e c o m p u t e d f r o mt h e r e g r e ss i o n e q u a t i o n r e la t in g p H a n d b a s e u n s a t u r a t i o n o f m u d s .T h e r e d u c t i o n o f p H in a b u f f e r s o l u t io n c a u s e d b y a k n o w n w e i g h t o fd r y m u d p r o v i d e d a n e s t im a t e o f to ta l e x c h a n g e a c id it y. N e u t r a l i z a ti o no f t h e t o t a l e x c h a n g e a c i d i t y w o u l d g i v e a b a s e u n s a t u r a t i o n o f 0 - 2 .T h e r e f o r e , t h e a m o u n t o f e x c h a n g e a c id i ty ( in m i l l ie q u i v a l e n t s ) w h i c hm u s t b e n e u t r a l i z e d t o l o w e r th e b a s e u n s a t u r a t i o n t o 0 -2 - - t h is c o r r e -s p o n d s t o 2 0 m g l it e r- ~ t o t a l h a r d n e s s a n d a l k a li n it y i n p o n d w a t e r - -w a s c a l c u l a t e d a s fo l lo w s :

A c i d i t y t o b e n e u t r a l i z e d = E x c h a n g e a c i d i t yI n it ia l b a s e u n s a t u r a t i o n - D e s i r e d b a s e u n s a t u r a t i o nx I n it ia l b a s e u n s a t u r a t i o n

B o y d a n d C u e n c o ( 1 9 8 0 ) d e t e r m i n e d t h a t a g r i c u l t u r a l l i m e s t o n er e a c t e d t o a d e p t h o f a p p r o x i m a t e l y 1 5 c m i n p o n d m u d s o v e r a 2 y e a rp e r i o d , a n d t h a t th e a i r - d r y w e i g h t o f t h e u p p e r 1 5 c m l a y e r o f m u d inp o n d s a v e r a g e d 1 4 0 0 0 0 0 k g h a - ~ . T h e a m o u n t o f a c id i ty to b en e u t r a l i z e d a s e s t i m a t e d f o r t h e s a m p l e m a y b e e x p a n d e d t o g i v e t h ea m o u n t o f a c i d it y to b e n e u t r a l i z e d i n th e p o n d m u d . T h e l im i n g r a tei n k i l o g r a m s p e r h e c t a r e o f C a C O 3 is c a l c u l a t e d f r o m t h e a c id i ty . A


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138 c. E. Bovdl iming fac to r o f 1 .5 i s m ul t ip l i ed by the l iming ra te , becau se agr i -cu l tu ra l l im es ton e i s no t 100% ef fec tive in neu t ra l i z ing so il ac id i ty .T h e m e t h o d d e v e l o p e d b y B o y d ( 1 97 4 ) h a s p r o v e n e f f e c t i v e , a n d i th a s b e e n w i d e l y u s e d . H o w e v e r , t h e p r o c e d u r e w a s d e v e l o p e d f o rp o n d s i n A l a b a m a , U S A , a n d r e l a t i o n s h i p s b e t w e e n p H a n d b a s eu n s a t u r a t i o n o f m u d s d i f f e r g e o g r a p h i c a ll y . F o r m o s t a c c u r a t e r e su l ts ,t he r e l a ti o n s h i p b e t w e e n p H a n d b a s e u n s a t u r a ti o n o f m u d s s h o u l d b ed e t e r m i n e d f o r e a c h r e g i o n w h e r e t h e p r o c e d u r e i s u s e d . T h i s i s ad i f f i cu l t t a sk tha t i s o f ten imprac t ica l . A s imple method fo r de te rmin-i n g t h e l i m e r e q u i r e m e n t o f p o n d m u d s t h a t d o e s n o t r e q u i r e d a t a o nt h e r e l a t i o n s h i p b e t w e e n p H a n d b a s e u n s a t u r a t i o n w a s d e v e l o p e d b yP i U a i a n d B o y d ( 1 9 8 5 ) . T h i s m e t h o d i n v o l v e s m e a s u r i n g t h e t o t a lexchange ac id i ty wi th a buf fe r , and ca lcu la t ing the l iming ra te neces -s a r y t o p r o v i d e a b a s e u n s a t u r a t i o n o f 0 . B e c a u s e t h i s t e c h n i q u e w i l la l w a y s p r o v i d e a h i g h e r l i m i n g r a te t h a n n e c e s s a ry , t h e l i m i n g f a c t o r o f1"5 is om itte d.

N o t a l l a c i d i t y p r o b l e m s i n p o n d s r e s u l t f r o m e x c h a n g e a c i d i t y .C a t ' s c la y , m i n e o v e r b u r d e n , a n d c e r t a i n o t h e r s o il s a r e a c i d ic b e c a u s eof the p resence o f pyr i t e (ac id -su l fa te so i l s ) . The so i l s have bo the x c h a n g e a n d s u l fu r ic a c id a c i d i ty ; B o y d ( 1 9 7 9 a ) p r e s e n t s a p r o c e d u r efor de te rmin ing the l ime requ i rement o f ac id -su l fa te so i l s . Ac id-su l fa te so i l s a re common in many coas ta l t rop ica l r eg ions , andresearch on neu t ra l i za t ion o f ac id -su l fa te so i l s on the wa te r sheds o ff is h p o n d s is b a d l y n e e d e d .W at e r e x c h a n g eT h e w a t e r r e t e n t i o n t i m e i n a p o n d h a s a p r o n o u n c e d i n f l u e n c e u p o npo nd fe r t i li za t ion and the res idua l e f fec t o f l ime app l ica t ions . I f wa te ri s r ap id ly f lushed th rough ponds , f e r t i l i ze r nu t r i en t s may be d i s -c h a r g e d b e f o r e t h e y c a n a f f e c t i n c r e a s e s i n p h y t o p l a n k t o n ; t h ein f luence o f l iming will be shor t - l ived . A l tho ug h the in f luence o f wa te rexchange ra te on fe r t i l i za t ion and l iming i s wide ly recogn ized in p rac -t i c e , t h e r e h a s b e e n n o r e s e a r c h t o p r o v i d e q u a n t i t a t i v e r e l a t i o n s h i p sbe tw een wa te r exch ange ra tes and the e f fec t iveness o f l iming and fe r t i-l ization.W e e d p r o b l e m sH i g h e r a q u a t i c p l a n t s c o m p e t e w i t h p h y t o p l a n k t o n f o r n u t r i e n t s .Th ere fo re , i f a pon d is in fes ted wi th aqua t ic weeds , f e r t i l iza t ion may


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Ma nagement o f environmental qualio' in aquaculture 139e n c o u r a g e t he g r o w t h o f w e e d s r a t h e r t h a n i n c re a s i n g p h y t o p l a n k t o np r o d u c t i o n . G r a s s c a r p m a y b e u s e d a s a b i o l o g i c a l c o n t r o l a g e n t , o rherb ic id es m ay be app l ied to a f fec t wee d c on t ro l be fore fe r t i l i za t ion isin i t ia ted .W a t e r c h e m i s t r y .I n w a t er s w i t h n a t u r a l l y h i g h p H a n d h i g h c a l c i u m c o n c e n t r a t i o n s , t h ep h o s p h a t e a p p l i e d i n fe r ti li z e rs m a y b e q u i c k l y p r e c i p i t a t e d f r o m t h ew a t e r a s a n i n s o l u b l e c a l c i u m p h o s p h a t e . H e n c e , t h e p h o s p h o r u sa p p l i c a t i o n r a t e m u s t b e g r e a t e r i n h a r d w a t e r o f h i g h p H t h a n i ns o f t e r w a t e r w i t h m o r e m o d e r a t e p H . T h e r e i s a l s o e v i d e n c e t h a tn u t r i e n t s i n a d d i t i o n t o n i t r o g e n a n d p h o s p h o r u s m a y l im i t p h y t o -p l a n k t o n p r o d u c t i v i t y i n s o m e w a t er s .T u r b i d i t yT u r b i d i t y r e s u l ti n g f r o m h i g h c o n c e n t r a t i o n s o f s u s p e n d e d c l ay p a r -t ic le s r es t ri c ts l i g h t p e n e t r a t i o n i n w a t e r a n d p r e v e n t s o p t i m u m g r o w t ho f p h y t o p l a n k t o n . T r e a t m e n t w i t h a l u m i n u m s u l f a t e ( a l u m ) o r g y p s u mwi l l r emove c lay tu rb id i ty qu ick ly , bu t un less the source o f the tu r -b id i ty i s e l imina ted the tu rb id i ty wi l l r e tu rn . Alum t rea tment i s themos t e f f i c ien t means o f removing tu rb id i ty (Boyd , 1979b) ; a t e s t fo rd e t e r m i n i n g t h e a l u m d o s e r a t e i s a v a i l a b l e . T h e u s e o f a l u m f o r t u r -b i d i ty r em o v a l is a n e x a m p l e o f t a k in g i n f o r m a t i o n f r o m a n o t h e r f ie l d( s a n i ta r y e n g i n e e r in g ) a n d d e v e l o p i n g m e t h o d o l o g y f o r a q u a c u l tu r e .W a t e r s h e d sPonds on fe r t i l e so i l s r equ i re l e ss fe r t i l i ze r fo r in i t i a t ion o f p lank tonb l o o m s t h a t p o n d s o n i n f e r ti l e s oils . M a n a g e m e n t o f w a t e r s h e d s a l soin t' luences po nd fe r t il i za tion . Bo yd (1976 ) dem on s t ra te d tha t unfe r ti -l i z e d p o n d s i n p a s t u r e s w e r e a s p r o d u c t i v e o f p h y t o p l a n k t o n a s f e r t i -l i z e d p o n d s , b u t u n f e r t i l i z e d p o n d s i n w o o d s w e r e m u c h l e s sproduc t ive than fe r t i l i zed ponds .

P r e v i o u s m a n a g e m e n tN u t r i e n t s a n d o r g a n i c m a t t e r t e n d t o a c c u m u l a t e i n f e r t i l i z e d p o n d so v e r t h e y e a r s . T h e r e f o r e a n o l d p o n d w i t h a h i s to r y o f f e r ti li z a ti o n


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140 C E. Boydd o e s n o t r e q u i r e a s m u c h f e r t i l i z e r a s a n e w e r p o n d . U n f o r t u n a t e l y ,t h e a g e a n d h i s t o r y o f p o n d s h a v e n o t b e e n c o n s i d e r e d i n p o n d f e rt il i-z a t i o n e x p e r i m e n t s .P h y t o p l a n k t o n c o m m u n i t i e sP o n d f e r t il i z a ti o n n o r m a l l y in c r e a s e s t h e a b u n d a n c e o f p h y t o p l a n k t o n ,b u t t h e t a x o n o m i c c o m p o s i t i o n o f t h e p h y t o p l a n k t o n i s u n p r e d i c t a b l e .A l t h o u ~ o n e c a n n o t d e f i n e t h e m o s t d e s i r a b l e p l a n k t o n i c t a x a f o r apar t i cu la r aqua cu l tu ra l sys tem , b lue -g reen a lgae a re genera l ly l e ssd e s i r a b l e t h a n g r e e n a l g a e , e u g l e n o p h y t e s , a n d d i a t o m s . U n f o r t u -n a t e ly , c u r r e n t f e r ti l iz a t i o n p r a c t i c e s o f t e n l e a d t o a p r e p o n d e r a n c e o fb l u e - g r e e n a l g a e. R e s e a r c h t o d e t e r m i n e t h e m o s t d e s i r a b l e p l a n k t o n i cf o r m s f o r f i sh c u lt u r e s y s t e m s a n d t o d e v e l o p t e c h n i q u e s f o r e n c o u r a g -i n g t h e g r o w t h o f th e s e f o r m s c o u l d p r o v e v a l u a bl e .W e a th e r a n d c l i m a t eI t is wide ly recogn ized th a t so i l f e r t il i ty and c rop m ana gem ent p rac -t i ces a re g rea t ly in f luenced by wea ther and c l imate . I a s sume tha tw e a t h e r a n d c l im a t e a l s o i n f lu e n c e t h e r e s p o n s e o f p o n d s t o fe r ti li z a-t io n . F o r e x a m p l e , d u r i n g a w e t y ea r , g r e a t e r w a t e r e x c h a n g e a n d m o r ec l o u d y w e a t h e r a r e l ik e l y t o r e s u l t i n l e ss p h y t o p l a n k t o n p r o d u c t i o nt h a n w o u l d b e e x p e c t e d f o r a n o r m a l y e a r . S i m i la r ly , p o n d s i n r e g io n sw i t h w a r m , d r y c l im a t e s w o u l d p r o b a b l y b e m o r e p r o d u c t i v e o f p h y t o -p l a n k t o n t h a n p o n d s i n r e g i o n s w i t h c o o l , w e t c l i m a t e s . H o w e v e r ,the re has been l i t t l e e f fo r t to inves t iga te the in f luence o f wea ther andc l imate on pond fe r t i l i za t ion .Ty pe o f f e r t il i z erB o y d ( 1 9 8 1 ) d e m o n s t r a t e d t h a t l i q u i d f e r t i l i z e r s w e r e m u c h m o r eef fec t ive than g ranu la r fe r t i l i ze r s fo r f i sh ponds . However , l iqu idfe r t i l i ze r s a re no t ava i lab le everywhere , and g ranu la r fe r t i l i ze r s wi l lc o n t i n u e t o b e u s e d i n m a n y p l a c e s . S e v e r a l d i f f e r e n t c h e m i c a l c o m -pounds a re used as sources o f l iqu id and g ranu la r fe r t i l i ze r s . Know-l e d g e o f th e m o s t s a t i s f a c to r y s o u r c e s f o r n i t r o g e n a n d p h o s p h o r u s f o rpond fe r t i l i za t ion i s bad ly needed , t expec t tha t the bes t nu t r i en ts o u r c e w o u l d d i f fe r a m o n g w a t e r s o f m a r k e d l y d i f f e re n t c h e m i st ry .


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M anagemen t o f environmental quali O" in aquaculture 141Culture speciesPhytoplankton abundance required for opt imum production of differ-ent aquacultural species probably varies. For example, experience atAuburn Univesity, Alabama, suggests that much greater abundance ofphytoplankton is required in the culture of Tilapia than in the cultureof Lepomis (sunfish). Pond fertilization research has been limited tocomparatively few species.

FISH FEEDINGFeeds are supplied to cultures of many species of fish to increase pro-duction above that obtained with fertilizers. Metabolic wastes fromfeed reach the water, exert an oxygen demand, and serve as a source ofnutrients for phytoplankton. The phytoplankton also exert an oxygendemand. Therefore, as feed rates increase, phytoplankton abun-dance increases, and water quality deteriorates. Considerable researchon the relationships between feeding of channel catfish and waterquality has been conducted at Auburn University. We have been ableto develop predictive equations and devise management strategies.Because similar relationships are likely to exist in other types of fishculture, a discussion of the findings seems appropriate here.Chem ical budgetsBudgets for water, nitrogen, phosphorus, chemical oxyen demand(organic matter), and dissolved oxygen (DO) were estimated over agrowing season (March-October) for three channel catfish ponds(Boyd, 1985). In addition to rainfall and runoff, 190 cm of water wereapplied from a pipe line to offset seepage and evaporation. Each kilo-gram of live fish required for production 1-32 kg of feed, and releasedto the water in metabolic wastes 51.1 g nitrogen, 72 g phosphorus,and 1"1 kg chemical oxygen demand (COD). Metabolic wastes result-ing from product ion of 1 kg of fish led to the synthesis of an additional2.59 kg of COD in photosynthesis. Thus, 1 kg of live fish resulted in3"69 kg COD. Fish harvest accounted for removal of only 26'8% ofnitrogen, 30-1% of phosphorus, and 25"5% of organic matter (COD)applied in feed. The remainder of the nitrogen and organic matter was


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142 C. E. B oyda p p a r e n t l y l o s t f r o m p o n d s , f o r n o a c c u m u l a t i o n o f t h e s e s u b s t a n c e sw a s d e t e c t e d i n m u d s . D e n i t r i f i c a t i o n a n d a m m o n i a v o l a t i l i z a t i o na p p a r e n t l y r e m o v e d l a r g e a m o u n t s o f n i t r o g e n ; o r g a n i c m a t t e r w a sc o n s u m e d i n r e s p i r a ti o n . M o s t p h o s p h o r u s n o t h a r v e s t e d i n f is h w a sa p p a r e n t l y a d s o r b e d b y m u d s . S e e p a g e a n d o v e r f l o w r e m o v e d o n l ys m a l l q u a n t i t i e s o f n i t r o g e n , p h o s p h o r u s , a n d o r g a n i c m a t t e r . P h y t o -p l a n k t o n p h o t o s y n t h e s i s p r o d u c e d l ar g e a m o u n t s o f D O , b u t 7 5 % o ft hi s D O w a s c o n s u m e d b y r e s p ir a t io n o f p h y t o p l a n k t o n a n d o t h e rm i c r o o r g a n i s m s w i t h i n t h e w a t e r c o l u m n . T o t a l r e s p i r a t i o n w i t h i np o n d s e x c e e d e d D O p r o d u c t i o n b y p h o t o s y n t h e si s , b u t d if fu s io n w a su s u a l l y a d e q u a t e t o m a i n t a i n a d e q u a t e D O c o n c e n t r a t i o n s f o r f i s hs u r v i v a l . H o w e v e r , m e c h a n i c a l a e r a t i o n w a s o c c a s i o n a l l y n e c e s s a r y t oprev en t f i sh m or ta l i ty .D i s s o l v e d o x y g e nS e v e r a l s t u d i e s h a v e d e m o n s t r a t e d t h a t f i s h e a t a n d g r o w b e s t a t d i s -s o l v e d o x y g e n ( D O ) c o n c e n t r a t i o n s n e a r a i r s a t u r a t i o n . H o w e v e r , i np o n d s i t is u s u a l ly i m p o s s i b l e t o m a i n t a i n D O c o n c e n t r a t i o n s n e a rs a t u r a t i o n a t n i g h t . M o s t w o r k e r s f e e l t h a t if D O d o e s n o t d r o p b e l o wa b o u t 2 5 % o f s a t u r a t i o n d u r i n g t h e n i g h t, a d e q u a t e l ev e ls o f f is h p r o -d u c t i o n m a y b e a c h i e v e d . N e v e r t h e l e s s , T u c k e r e t a l . ( 1 9 7 8 ) d e m o n -s t r a t e d t h a t c h a n n e l c a t f i s h p r o d u c t i o n i n c r e a s e d w i t h i n c r e a s i n ga v e ra g e c o n c e n t r a t i o n s o f D O a t d a w n .T h e c o n c e n t r a t i o n o f D O a t d a w n d e c r e a s e s a s f e e d i n g r a t ei n c r e a s e s , a n d a t h i g h f e e d i n g r a t e s e m e r g e n c y a e r a t i o n m u s t f r e -q u e n t l y b e a p p l ie d d u r i n g e a r ly m o r n i n g h o u r s to p r e v e n t D O d e p l e -t i o n a n d f i s h m o r t a l i t y . B o y d e t a l . ( 1 9 7 8 ) d e v e l o p e d a m e t h o d f o rp r e d i c t i n g t h e i n s t a n t a n e o u s r a t e o f c h a n g e o f D O d u r i n g d a r k n e s s(DO,) wi th respec t to t ime :

d D O ~d t- - - -+ D 'O dt - D O t- - D 'Om - D 'Op

wh ere D 'Odf i s the ra te o f ga in o r loss o f O , to d i f fus ion ; D O t i s the ra teo f 0 2 c o n s u m p t i o n b y f is h ; D 'O m is t h e r a t e o f l o ss o f 0 2 t o b e n t h i cresp i ra t ion ; DOp is t h e r a te o f 0 2 c o n s u m p t i o n b y th e p l a n k t o n i c c o m -mu ni ty . (The do t no ta t ion re fe r s to t im e der iva t ives ; x = d x / d t . )M e t h o d s , e q u a t i o n s , a n d t a b u l a r f u n c t i o n s f o r e s t i m a t i n g D 'O d f ,DOt-, D 'O m , a n d D 'O p a r e p r e s e n t e d b y B o y d e t a l . ( 1 9 7 8 ) . T h e D O


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M anagemen t of environmental quali O, in aquaculture 14 3c o n c e n t r a t io n a t d a w n m a y b e c o m p u t e d b y i n te g r a ti n g t h e i n s ta n t a -neous ra te func t ion as fo l lows :

I ,, -J~n d D O nDOd~wn= DOdusk +d r . = d u s k d t d t

T h e m e t h o d w a s r e li a b le in p re d i c ti n g D O c o n c e n t r a t io n s a t d a w n .R o m a i r e a n d B o y d ( 1 9 7 9 ) d e v e l o p e d a n e q u a t i o n b a s e d o n s o l a rr a d i a ti o n , c h l o r o p h y l l a , a n d D O s a t u r a t i o n a t d a w n f o r e st im a t i n g t h ec h a n g e i n D O c o n c e n t r a t i o n b e t w e e n d a w n a n d d u s k ( AD O d~ y). T h ed a y - t i m e e q u a t i o n w a s c o u p l e d t o t h e n i g h t - t i m e e q u a t i o n t o p e r m i ts i m u l a ti o n of D O c o n c e n t r a t io n s o v e r o n e o r m o r e d a y s :

I t = d usD O d us k = D O d aw n -t- A D O d ~ y - (D O t -) d t

t, , = a ' o , ' n

S i m u l a t i o n s p e r m i t t e d e s t i m a t i o n s o f t h e i n f lu e n c e o f d if f e re n t v a l u esf o r p h y t o p l a n k t o n d e n s i t y , s o l a r r a d i a t i o n , t e m p e r a t u r e , a n d f i s hs t a n d in g c ro p o n D O r eg im e s .A e r a t i o nT w o t y p e s o f a e r a t i o n h a v e b e e n e m p l o y e d i n c h a n n e l c at f is h p o n d s - -e m e r g e n c y a e r a t i o n a n d s u p p l e m e n t a l a e r a t i o n . E m e r g e n c y a e r a t i o nh a s b e e n c o n d u c t e d p r i m a r i l y w i t h l a rg e t r a c t o r - p o w e r e d a e r a t o r sw h i c h q u i c k l y r a is e D O c o n c e n t r a t i o n s a n d p r e v e n t f is h s t re s s a n dm o r t a li ty . S u p p l e m e n t a l a e r a t i o n i s u s e d d u r i n g n i g h t - t i m e h o u r s i n a na t t e m p t t o i n c r e a s e f is h p r o d u c t i o n b y p r e v e n t i n g c ri t ic a l ly l o w D Oc o n c e n t r a t io n s a n d t o r e d u c e d e p e n d e n c e u p o n e m e r g e n c y a e ra t io n .E m e r g e n c y a e r a t i o n i s a p r o v e n m a n a g e m e n t t o o l th a t is e s s e n ti a l inc o m m e r c i a l p r o d u c t i o n o f c h a n n e l c a t f i s h . A t f e e d i n g r a t e s i n e x c e s so f 4 0 - 5 0 k g h a -~ d a y - ~, D O d e p l e t i o n a n d f is h d e a t h s a r e l ik e l y t oo c c u r i n a c h a n n e l c a t fi s h p o n d d u r i n g e a c h g r o w i n g s e a s o n ( T u c k e r eta t., 1 9 7 8) . A r m s t r o n g a n d B o y d ( 1 9 8 2 ) a n d P e t ri ll e a n d B o y d ( 1 9 8 4 )d e v e l o p e d p r o c e d u r e s f o r te s ti n g t h e p e r f o r m a n c e o f e m e r g e n c y a e r a -t i o n d e v i c e s . L a r g e p a d d l e w h e e l a e r a t o r s a n d p u m p i n g - s p r a y e rdev ices a re the m os t e f fec t ive types .

S u p p l e m e n t a l a e r a t i o n w i t h s m a l l e l e c tr i c a e r a t o r s h a s i n c r e a s e d t h ep r o d u c t i o n o f c h a n n e l c a t f is h i n r e s e a r c h , b u t t h e e c o n o m i c a d v a n t a g eo f s u p p l e m e n t a l a e r a t i o n i n c o m m e r c i a l p r o d u c t i o n is u n c e r t a in .


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144 C. E . BoydS h e l t o n a n d B o y d ( 1 9 8 3 ) p r e s e n t e d a m e t h o d f o r es t im a t i n g o x y g e n -t r a n s f e r r a t e s o f s u p p l e m e n t a l a e r a t o r s i n f i s h p o n d s . H o w e v e r , t h e r ei s c u r r e n t l y n o p r o c e d u r e f o r e s t i m a t i n g t h e i n c r e a s e i n f i s h p r o d u c -t io n t h a t c a n b e e x p e c t e d f r o m a N v e n a m o u n t o f s u p p l e m e n t a l a e r a -t ion . Wi thou t th i s in fo rmat ion , i t i s imposs ib le to eva lua te the benef i to f s u p p l e m e n t a l a e r a t i o n .F e e d i n g r a t e s a n d w a t e r q u a l i tyC o l e a n d B o y d ( 1 9 8 6 ) e s t a b l i s h e d m a x i m u m d a i l y f e e d i n g ra t e s o f 0 ,2 8 , 5 6, 84 , 1 1 2 , 1 6 8 , a n d 2 2 4 k g h a - l i n c h a n n e l ca tf is h p o n d s . A e r a -t i o n w a s s u p p l i e d a t 6 . 1 k W h a - I w h e n D O c o n c e n t r a t i o n s w e r ee x p e c t e d t o f al l b e l o w 2 m g l it e r -~ . S t r o n g c o r r e l a t io n s ( r = 0 " 8 5 t o0 "9 8) w e r e o b s e r v e d b e t w e e n f e e d i n g ra t e s (X ) a n d c o n c e n t r a t i o n s ( Y )o f D O a t d a w n , c h o l o r o p h y l l a , c h e m i c a l o x y g e n d e m a n d , c a r b o nd i o x i d e , a n d t o t a l a m m o n i a n i t r o g e n . T h e c o r r e l a t i o n f o r D O w a snega t ive . L i t t l e ae ra t ion was requ i red a t f eed ing ra tes o f 56 kg ha- ~o rl e s s ; a e r a t i o n w a s a p p l i e d a l m o s t c o n s t a n t l y a t n i g h t i n p o n d s w i t hf e e d in g r a te s o f t l 2 k g h a- ~ d a y - ~ a n d a b o v e . N e t f i sh p r o d u c t i o nw a s c o r r e l a t e d ( r =0 '9 9 ) w i t h f e e d i n g r a t e u p t o a m a x i m u m d a i l yfeed ing ra te o f 112 kg ha - ~. Feed c on ver s ion ra t ios ( feed app l ied + ne tf i sh p ro duc t ion) were a l so essen t ia l ly con s tan t up to a feed ing ra te o f1 1 2 k g h a - ~ d a y - ~ . A t h i g h e r f e e d i n g r a t e s , f e e d c o n v e r s i o n r a t i o si n c r e a s e d a n d f i sh p r o d u c t i o n d e c l i n e d .W a t e r q u a l i ty d e t e r i o r a t i o n o b v i o u s l y l i m i ts t h e a m o u n t o f f ee d t h a tcan be ap p l ied wi th a g iven ae ra t ion reg ime . It i s a l so appa ren t tha t thea m o u n t o f a e r a t i o n m u s t b e l i m i t e d b y c o s t f a c t o r s . H o w e v e r , e v e n i fe c o n o m i c c o n s i d e r a t i o n s a r e i g n o r e d , a n d e n o u g h a e r a t i o n i s a p p l i e dt o p r e v e n t l ow D O a t u n u s u a l l y h ig h f e e d i n g ra t e s, f is h p r o d u c t i o n w i lln o d o u b t b e l i m i t ed b y l a rg e c o n c e n t r a t i o n s o f a m m o n i a .N i t r o g e n o u s w a s t e p r o d u c tsT h e a c c u m u l a t i o n o f a m m o n i a a n d t h e p r o d u c t i o n o f n i t r i t e h a sresu l ted in reduc t ion in ca t f i sh g rowth and in mor ta l i ty o f ca t f i sh . Thetox ic i ty o f am m on ia and n i t r i t e to ca t f i sh has been s tud ied , bu t the re i sa n i n c o m p l e t e k n o w l e d g e o f f a c t o r s r e g u l a t i n g t h e c o n c e n t r a t i o n s o fa m m o n i a a n d n i t r i t e i n p o n d w a t e r . R e s e a r c h i n t h i s a r e a i s b a d l yn e e d e d .


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Ma nagement of environmental quali~' in aquaculture 145C O N C L U S I O N S

T h e e n v i r o n m e n t w i th i n p o n d c u l tu r e s ys te m s is d y n a m i c a n d c o m -p l e x , a n d t h e q u ality ," o f t hi s e n v i r o n m e n t h a s p r o f o u n d i n f l u e n c e su p o n f i s h p r o d u c t i o n . E f f e c t i v e m a n i p u l a t i o n o f t h e e n v i r o n m e n t t of a v o r g r e a t e r f i s h p r o d u c t i o n r e q u i r e s a n u n d e r s t a n d i n g o f b a s i cp h y s i ca l , c h e m i c a l , a n d b i o l o g ic a l p r o c e s s e s . E n v i r o n m e n t a l c o n d i -t io n s d i ff e r w i t h in a p o n d o v e r t i m e a n d a m o n g p o n d s i n d i f fe r e n tl o ca li ti es . T h e s e d i f f e r e n c e s m u s t b e c o n s i d e r e d w h e n d e v e l o p i n gp r o c e d u r e s f o r e n v i r o n m e n t a l m a n a g e m e n t . M o d e l s a n d s i m u l a t i o nt e c h n i q u e s a r e n e c e s s a r y i n r e s e a r c h o n e n v i r o n m e n t a l q u a l i t y i na q u a c u l t u r e .

R E F E R E N C E SA rm st rong , M . S. & Boyd , C. E . (1982). Ox ygen -t ransfer ca lcula tions for at rac tor -powe red pad dlewh ee l ae ra tor . Trans. Am. Fish. Soc., 111 , 361 - 6 .Boyd, C. E . (1974). Lim e requ i reme nts of A labam a fi sh pond s . A labam aAgricul tura l Exper iment Sta t ion, Auburn Univers i ty , Ala. Bull . , 459 ,19 pp.Boyd, C. E . (1976) . Water chemis t ry and plankton in unfer t i l i zed ponds inpas tures and in wo ods . Trans. Am. Fish. Soc., 1 0 5 , 6 3 4 - 6 .Boyd, C. E . (1979a) . Water qua l i ty in wa rm wa ter f i sh ponds , Alabama Agr i -cul tura l Ex per im ent Stat ion, Aub urn Univesity, Alaba ma , 359 pp.Boyd , C. E . (1979 b) . A lum inum sul fate (a lum) for prec ipi ta ting c lay turbidi tyfrom f ish ponds . Trans. Am. Fish. Soc., 1 0 8 , 3 0 5 - 1 i .Boy d, C. E. ( 1981). Co m pa riso n of f ive ferti l izat ion prog ram s for f ish pond s.Trans. Am. Fish. Soc., 1 1 0 , 5 4 1 - 5 .Boyd , C. E . (1985) . C hem ica l budg ets for channel ca tf i sh ponds . Trans. Am.

Fish. Soc., 1 1 4 , 2 9 1 - 8 .Boyd, C. E . & Cuenco, M. L. (1980) . Ref inements of the l ime requi rementproc edu re fo r f ish ponds . A q u a cu l t u r e , 2 2 , 2 9 3 - 9 .Boy d, C. E ., Rom aire , R . P. & Joh nston , E . (1978) . Predic t ing ear ly mo rningdissolved oxygen conc ent ra t ions in chan nel cat fish pond s . Trans. A m . Fish.Soc. , 1 0 7 , 4 8 4 - 9 2 .Co le, B. A. & Boy d, C. E. (1986). Fee ding rates, w ater quali ty, and ch ann elca tf ish p rod uct io n in ponds . Prog. F ish-Cul t ., 48 , 25 - 9 .Petri l le , J . & Boyd, C. E. (1984). Comparisons of oxygen-transfer rates andwater-c i rcula t ing capabi li ti es of em erge ncy aera tors for f ish pond s . A q u a -culture, 3 7 , 3 7 7 - 8 6 .Pi l la i , V. K. & Boyd, C. E. (1985). A simple method for determining l imerequ i reme nts of fish ponds . A q u a cu l t u r e , 46 , 157-62 .


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146 C E. BoydRomaire, R. R & Boyd. C. E. (1979). Effects of solar radiation on thedynamics of dissolved oxygen in channel catfish ponds. Trans. Am. Fish.

Soc., 108,473-8.Shelton, J. L. Jr. & Boyd, C. E. (1983). Correction factors for calculatingoxygen-transfer rates of pond aerators. Trans. Am. Fish. Soc., 112, 120-2.Tucker, L., Boyd, C. E. & McCoy, E. W. (1978). Effects of feeding rate onwater quality, production of channel catfish, and economic returns. Trans.Am. Fish. Soc., 108, 389-96.

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Boyd 1986 Aquacultural-Engineering