the environmental impact of marine

8/11/2019 The Environmental Impact of Marine

1/8

Pergamon

O025-326X(95)OOlOO-X

Marine Pol lut ion Bulle t in Vol. 31, Nos 4-12, pp. 159-166, 1995

Copyright 1995 Elsevier Science Ltd

Printed in Great Britain. All rights reserved

0025-326X/95 9.50 + 0.00

T h e E n v ir o n m e n t a l Im p a c t o f M a r i n e

F i s h C u l tu r e T o w a r d s a S u s t a in a b l e

F u t u r e

R . S . S . W U

Biology and Chemistry Department City University of Hong Kong Tat Che e Avenue Kowloon Hon g Kong

The envi ronmenta l impac t of mar ine f i sh- fa rming depends

very much on spec ies , cu l ture me thod, s tocking dens i ty ,

f e e d t y p e , h y d r o g r a p h y o f t h e s i t e a n d h u s b a n d r y

p r a c ti c e s . I n g e n e r al , s o me 8 5 o f p h o s p h o ru s , 8 0 - 8 8

o f c a r b o n a n d 5 2 - 9 5 o f n i t ro g e n i n p u t i n to a ma r in e fi sh

c u l t u re s y s t e m a s f e e d m a y b e l o s t in to t h e e n v ir o n me n t

through feed was tage , f i sh exc re t ion , f aeces produc t ion

a n d r e s p i ra t i o n . C l e a n in g o f f o u l e d c a g e s ma y a l s o a d d a n

organic loading to the wa te r , a lbe i t pe r iod ica l ly . P rob lem s

caused by h igh orga nic and nut r ien t loadings conf l ic t wi th

o th e r u s e s o f t h e c o a s t a l z o n e . T h e u s e o f c h e mic a l s

( the rapeutan ts , v i tamins and an t i fou lan ts ) and the

in t roduc t ion o f pa tho gens a nd new gene t ic s t r a ins have

a lso r a i sed envi ronmenta l conce rns .

esp i t e the

high pol lu t ion loadings , r e su l t s f rom va r ious

s t ud i es s h o w t h a t s o m e 2 3 o f C , 2 1 o f N a n d 5 3 o f

P of f eed input in to the cu l ture sys tem is be ing

accumula ted in the bot tom sediments and the s ign i f ican t

imp a c t i s n o r ma l ly c o n f in e d t o w i th in 1 k m o f t h e f a r m.

T h e ma jo r imp a c t i s o n t h e s e a b o t t o m, w h e r e h ig h

sediment oxygen demand, anoxic sed iments , p roduc t ion of

tox ic gas es and a dec rease in benth ic d ive r s i ty m ay re su l t .

Decreases in d isso lved oxygen and inc reases in nu t r ien t

leve ls in the wa te r a re a l so ev ident bu t a re normal ly

conf ined to the v ic in i ty of the f a rm. Tr ibuty l t in (TBT)

contamina t ion and the deve lopment of an t ib io t ic - re s i s tan t

bac te r ia have been repor ted nea r f i sh f a rms . The

s t imula t ing e f fec ts of v i tamins / f i sh was te s on growth of

red t ide spec ies have been demonst ra ted in a number of

labora tory s tud ies . Never the le ss , the re i s no ev idence to

suppor t the sugges t ion tha t the present use of the rapeu-

tan ts , v i tamins and an t ib io t ic s and the in t roduc t ion of

pa thogen s and new gene t ic s t r a ins w ould pose a s ign if ican t

threa t to the envi ronment .

Mar ine f i sh cu l ture can be a sus ta inable deve lopment ,

provided pol lu t ion loadings gene ra ted by f i sh f a rms a re

k e p t w e l l b e lo w th e c a r r y in g c a p a c i t y o f th e w a t e r b o d y .

Ef fec ts can be s ign i f ican t ly r educed by ca re fu l

s i t e

se lec t ion , cont ro l o f s tock dens i ty , improved feed

formula t ion and in tegra ted cu l ture (wi th macroa lgae ,

f i l te r - f eede r s and depos i t - f eede r s ) . An example of the

a p p l ic a t io n o f c o m p u te r m o d e ll i ng i n m a r i c u lt u r e ma n a g e -

me n t i s d e mo n s t r a t e d . E n v i r o n me n ta l imp a c t a s s e s s me n t

and moni tor ing should a lso be ca r r ied out to ensure

cul ture ac t iv i t ie s a re envi ronm enta l ly sus ta inable .

Ma r in e f i s h ma y b e c u l t u r e d i n r a c e w a y s , p o n d s o r n e t

c a g e s i n o p e n w a t e r s . S a lmo n id f i s h c u l t u r e p r e d o mi -

n a t e s i n w e s t e r n E u r o p e , S c a n d in a v i a a n d N o r th

A me r i c a , w h e r e a r t i f i c i a l f e e d i s c o mmo n ly u s e d . I n

A s i a n - P a c i f i c w a t e r s ( e . g . J a p a n , K o r e a , H o n g K o n g ,

T h a i l a n d , M a la y s i a a n d S in g a p o r e ) , a v a r i e ty o f n o n -

sa lm onid spec ies ( e.g. g roup ers , sea bream s, seabas s ,

s n a p p e r s a n d y e l l o w t a il s ) i s c o m mo n ly c u l t u r e d a n d f e d

w i th t r a s h f i sh . M a r in e f is h c u l t u r e i n t h e c o a s t a l w a t e r s

o f ma n y c o u n t r i e s h a s g r o w n d r a m a t i c a l l y i n r e ce n t

y e a r s , a n d f u r t h e r g r o w th i s e x p e c t e d i n t h e c o min g

d e c a d e ( F A O , 1 9 92 ). T h e r a p id g r o w th o f ma r in e f i sh -

f a r min g h a s a l r e a d y l e d t o g r o w in g c o n c e r n s o v e r

e n v i r o n m e n ta l im p a c t s a n d c o n f l i c ts w i th o th e r c o a s t a l

u s a g e i n E u r o p e , N o r t h A m e r i c a , A u s t r a l i a a n d A s i a

( H a mm o n d , 1 9 8 7; W a ld i c h u c k , 1 9 8 7 a , b ; M o r to n , 1 9 89 ;

M i k i et al. 1 9 9 2 ) . I n d e e d , e n v i r o n me n ta l c o n c e r n s h a v e

l e d t o a m o r a t o r i u m o n n e w d e v e l o p m e n t s a n d t i g h te r

c o n t r o l i n N e w Z e a l a n d , D e n m a r k , N o r w a y , C a n a d a

a n d H o n g K o n g ( D u f f, 1 98 7; B C M i n i s tr y o f E n v i r o n -

me n t , 1 9 9 0 ) . I n S c o t l a n d a n d H o n g K o n g , t h e r e i s a

g e n e r a l t e n d e n c y t o f o r c e ma r in e f i s h - f a r min g o f f s h o r e

(Aldr idge, 1988) .

T h i s p a p e r 1 . c o n s id e r s t h e p o l l u t a n t s g e n e r a t e d f r o m

ma r in e f i s h - f a r min g a n d t h e i r e n v i r o n me n ta l f a t e s , 2 .

r e v i ew s t h e imp a c t o f ma r in e f i s h -f a r min g o n t h e m a r in e

e n v i r o n me n t , a n d 3 . e x a min e s p r a c t i c a l mi t i g a to r y

me a s u r e s w i th a v i e w to ma k in g ma r in e f i s h - f a r min g a

s u s t a in a b l e d e v e lo p me n t .

Sources K inds Form s and Fa te s o f Po l lu tan t s

H ig h o r g a n i c a n d n u t r i e n t l o a d in g s a r e ma in ly

g e n e r a t e d f r o m f e e d w a s t a g e , f i s h e x c r e t i o n a n d f a e c a l

p r o d u c t i o n . M o s t o f o u r k n o w l e d g e o f fe e d w a s t a g e,

o r g a n i c a n d n u t r i e n t l o a d in g s a n d N e x c r e t i o n a r e ,

h o w e v e r , o n ly b a s e d o n s a lmo n id f i s h c u l t u r e d i n l a n d

fac il i tie s f ed wi th a r t if ic ia l f eed ( for a r ev iew, see Go w en

& B r a d b u r y , 1 9 8 7 ; H a n d y & P o x to n , 1 9 9 3 ) . P o l l u t i o n

lo a d in g s a n d e f f l u e n t q u a l i t y f r o m l a n d - b a s e d f a r ms

h a v e b e e n w e l l d o c u m e n te d ( A la b a s t e r , 1 9 82 ), w h i l e

th o s e f r o m o p e n - s e a c a g e f a r ms a n d , p a r t i c u l a r l y , t h o s e

f r o m n o n - s a l m o n i d s p e ci es a r e p o o r l y k n o w n ( H a n d y &

P o x to n , 1 9 93 ). F e e d w a s t a g e i s o n e o f t h e mo s t

imp o r t a n t s o u r c e s c o n t r i b u t i n g t o o r g a n i c a n d n u t r i e n t

159


2/8

l o a d in g s ( A c k e f o r s & E n e l l, 1 9 90 ; S e y mo u r & B e r g h e im,

1 9 91 ). W a s t a g e ma y r a n g e f r o m 1 - 3 8 , d e p e n d in g o n

th e f e e d t y p e , f e e d p r a c t ic e s , c u l t u r e m e th o d a n d sp e c ie s

( W a r r e n - H a n s e n , 1 98 2; O v e A r u p e t a l . 1 9 89 ; T h o r p e e t

a l . 1990; Bever idg e e t a l . 1 9 91 ). H o w e v e r , t h e r e a r e f e w

p u b l i sh e d e s t im a te s o f f e e d w a s t a g e a n d t h e l imi te d

a v a i l a b l e d a t a a r e e x c lu s iv e t o s a lmo n id s c u l t u r e d i n

p o n d s ( H a n d y & P o x t o n , 1 99 3) . D e p o s i t i o n o f o r g a n ic

w a s t e w a s e s t ima te d a t 3 k g m - 2 y r - 1 i n t h e v i cin i ty o f a

f a r m a n d 1 0 k g m - 2 y r - 1 o r 1 . 8 -3 1 . 3 k g C m - 2 y r - 1

u n d e r n e a th ( G o w e n & B r a d b u r y , 1 9 8 7 ) . F lu x e s a n d

ma ss b a l a n c e s o f C , P a n d N d e t e r min e d f o r a sa lmo n id

c a g e f a r m ( r a in b o w t r o u t f e d w i th d r y f e e d ) i n d i c a t e d

t h a t 8 0 o f C , 7 6 o f N a n d 8 2 o f P o f f e ed i n p u t

in to t h e sy s t e m w e r e l o s t t o t h e e n v i r o n m e n t ( H a l l e t a l .

1 9 9 0 ; H o lb y & H a l l , 1 9 9 1 ; H a l l e t a l . 1992) . The to ta l

e n v i r o n m e n t a l l o ss o f N w a s e s t im a t e d a t b e t w e e n 9 5 -

1 02 k g N t - 1 p r o d u c t i o n ( H a l l e t a l . 1992) , and depos i t s

f r o m f i sh f a r ms c o v e r e d so me 3 . 8 t ime s t h e a r e a o f t h e

f a r m i t s e l f ( H a l l

e t a l .

1990).

A c o m p a r i s o n o f f ee d w a s t a g e a n d p o l l u t i o n l o a d i n g s

f r o m 1 . r a in b o w t r o u t c u l t u r e d i n a r a c e w a y a n d f e d

w i th d r y f e e d i n E u r o p e , 2 . s a lmo n id s c u l t u r e d i n p o n d s

a n d f e d w i th a r t i f i c i a l f e e d s i n E u r o p e , a n d 3 . g r o u p e r s

a n d sn a p p e r s c u l t u r e d i n o p e n - se a c ag e s a n d f e d w i th

t r a sh f i sh i n H o n g K o n g , i s g iv e n in F ig s 1 a n d 2 . It i s

o b v io u s t h a t r e g a r d l e s s o f sp e c i e s a n d c u l t u r e me th o d s ,

ma r in e f i sh - fa r min g g e n e r a t e s a v e r y h ig h p o l lu t i o n

l o a di n g . F e e d w a s t a g e a n d p o l l u t a n t l o a d i n g s a r e m u c h

h ig h e r i n o p e n - se a c a g e c u l t u r e sy s t e ms w h e r e t r a sh f i sh

is used a s f eed .

I n a E u r o p e a n s a lmo n id f a r m u s in g a r t i f i c i a l f e e d , i t

w a s e s t im a t e d th a t e v e n t u a ll y s o m e 8 0 - 8 4 o f C , 5 2 -

9 5 o f N a n d 8 2 o f P i n t h e f e e d m a y b e l o s t t o t h e

e n v i r o n me n t ( T a b l e 1 ) . C a r b o n ma y b e l o s t i n to t h e

e n v i r o n me n t t h r o u g h f e e d w a s t a g e a n d f ish r e sp i r a ti o n

( in t h e f o r m o f

C O 2 ) .

N u t r i e n t s ( N a n d P ) m a y b e l o s t

t h r o u g h e x c r et i o n ( m a i n ly i n t h e f o r m o f am m o n i c a l N

a n d u r e a ) , f e e d w a s t a g e a n d f a e c a l p r o d u c t io n ( ma in ly

in o r g a n i c f o r ms ) .

D e sp i t e h ig h o r g a n i c a n d n u t r i e n t l o a d in g s d e p o s i t e d

o n th e b o t t o m s e d im e n t , o n l y 1 0 o f o r g a n ic m a t t e r in

M a r i n e P o l l u t i o n B u l l e t in

t h e s e d ime n t u n d e r n e a th s a lmo n id f a r ms i s b r o k e n

d o w n a n n u a l ly ( A u r e & S t ig e b r a n d t , 1 9 9 0 ) , a n d

d e c o m p o s i t i o n o f f a rm d e p o s i ts h a s b e e n s h o w n t o b e

in v e r se ly r e l a t e d t o n e t a c c u mu la t i o n ( H a n se n e t a l .

1990) . Sedim ent f luxes of C , N and P a re ve ry low, and

7 9 o f C , 8 8 o f N a n d 9 5 o f P i n f a r m d e p o s i ts

( e q u iv a l e n t t o 2 3 o f C , 2 1 o f N a n d 5 3 o f P o f t h e

f e e d i n p u t ) w i l l b e a c c u mu la t e d i n t h e s e d ime n t a n d

b e c o m e u n a v a i l a b l e ( T a b l e 1 ). H a n d y & P a x to n ( 19 9 3)

a l so e s t ima te d t h a t 5 9 - 6 6 o f P i n t h e f e e d i s

a c c u mu la t e d i n t h e s e d ime n t . P h o sp h o r u s c a n b e

r e c y c le d to w a te r b y d e so r p t i o n a n d b io lo g i c a l p r o c e s se s

b u t t h e r e l e ase b e c o m e s i n sig n if i ca n t w h e n th e d e p o s i t i s

> 7 c m th i c k ( H a n se n e t a l . 1990) . Since N mineraliza-

t ion ma in ly occurs in ox ic sur face sed iments , the ra te

w o u ld b e v e r y s lo w in d e p o s i t s u n d e r n e a th f a r ms w h e r e

th e s e d ime n t i s n o r ma l ly a n a e r o b i c a n d w i th o u t

b io tu r b a t i o n a n d e p i f a u n a l r e w o r k in g ( R u b le e , 1 9 8 2 ;

Hue t te l , 1990) . Indeed , Kaspa r

e t a l .

(1988) fa iled to

de tec t in - s i tu n i t r i f ica t ion in sed iment d i rec t ly under a

sa lmo n id f a r m.

Vita m ins (e .g. B12 an d b iotin) , an tibio tics (e .g.

a u r e o my c in , o x y t e t r a c y c l i n e , t e r r a my c in , f u r a z o l id o n e

a n d n i t r o f u r a z o n e ) a n d p ig me n t s a r e o f t e n a d d e d t o

a r ti f ic i al f e e d b u t su c h a d d i t i o n s a r e n o t c o m m o n in t h e

t r o p i c s a n d su b - t r o p i c s w h e r e t r a sh f i sh i s p r e d o min -

ant ly used a s a f eed . Therapeutan ts ( e .g . ma lachi te

g r e e n , f o r ma l in , c o p p e r su lp h a t e a n d d ip t e r e x ) a r e

c o mmo n ly u se d t o t r e a t f i sh d i s e a se s . T o x ic c h e mic a l s

( me ta l s a n d so m e t ime s T B T ) a r e o f t e n u se d t o t r e a t c a g e

n e t t i n g t o c o n t r o l f o u l i n g ( D a v ie s & Mc K ie , 1 9 8 7 ;

T h r o w e r & S h o r t , 1 9 9 1 ) , a l t h o u g h th e i r u se h a s b e e n

b a n n e d i n ma n y c o u n t r i e s s i n c e 1 9 9 0 . A la b a s t e r ( 1 9 8 2 )

e s t ima te d t h a t t h e u se o f t h e r a p e u t a n t s ( a u r e o my c in ,

o x y te t r a c y c l i n e , t e r r a my c in , f u r a z o l id o n e a n d n i t r o f u r -

a z o n e) w a s b e t w e e n 7 0 - 2 0 0 0 m g k g - x f ee d . In N o r w a y ,

th e u se o f t h e r a p e u t a n t s f o r f i sh - f a rmin g ( n i tr o -

furazol idone , oxyte t racyc l ine , oxol in ic ac id , su lphamer -

a z in e a n d t r ime th o p r im- su lp h a d i a z in e ) h a s i n c r e a se d

f rom 3 .7 t in 1980 to 32 .6 t in 1988 (Grave e t a l . 1990);

a n d i t w a s e s t ima te d t h a t so me 4 3 0 g o f a n t i b io ti c s w a s

u se d in p r o d u c in g 1 t o f s a lmo n ( R o se n th a l e t a l . 1988).

D r y F e e d

Raceways)

M o i s t F e e d

Ponds)

Trash

F ish

Open sea cages)

5 1 1 5 2 2 5 3

35 40 45 50

i G Maximum

Minimum

Feed W astage ( )

]big. 1 Fe e d wa s ta ge r e su l t ing f rom the use of v a r ious f e e d types .

Cul ture m e th ods o f e a c h s tudy a re shown in pa re nthe se s . a Ove

A m p

e t a l .

1989; bW a r re n-Ha nse n , 1982.)

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Volume 31/Num bers 4--12/April-December 1995

K ~ I , t -1 p r o d u c t i o n

snappers

T

Fig. 2. Pollution loadings resulting from various types o f culture and

species (TN : total N; T P: total P; data from: IW arren-Hansen,

1982; 2Alabaster, 1982; Hand y & Poxton, 1993; 3Ove Arup e t

a l . 1989).

S t a ti s ti c s o n t h e u s e o f c h e m i c a l t h e r a p e u t a n t s i n o t h e r

c o u n t r i e s i s n o t a v a i l a b l e , b u t t h e q u a n t i t y u s e d i s

e x p e c t e d t o b e l a r g e ( C h u a , 1 9 9 3 ) . T h e q u a n t i t i e s o f

t h e r a p e u t i c c h e m i c a l s r e l e a s e d i n t o t h e e n v i r o n m e n t ,

h o w e v e r , r e m a i n v i r t ua l l y u n k n o w n .

T h e P a n d N l o a d i n g g e n e r a t e d f r o m f i s h - fa r m i n g

c o r r e s p o n d s t o a n e g l i g i b l e f r a c t i o n ( 0 . 6 % a n d 0 . 2 % ,

r e s p e c t iv e l y ) o f o v e r a l l l o a d i n g s o n c o a s t a l a r e a s o f

S w e d e n , b u t l o c a l e f fe c t s m a y b e s i g n i fi c a n t (A c k e f o r s &

E n e l l , 1 9 9 0 ) . S i m i l a r l y , t h e i m p a c t o f m a r i n e f i sh -

f a r m i n g w a s c o n s i d e r e d l o w c o m p a r e d w i t h o t h e r w a s t e

g e n e r a t i n g a c t i v it ie s a l o n g t h e w e s t c o a s t o f C a n a d a ( B C

M i n i s t ry o f E n v i r o n m e n t , 1 99 0) . I n H o n g K o n g , w h e r e

o p e n - c a g e c u l t u r e i s p r a c t i s e d a n d t r a s h f i s h i s u s e d ,

B O D a n d N , g e n e r a t e d b y t he m a r i c u l t u re i n d u s tr y ,

c o n s t i tu t e d a b o u t 3 % o f t o ta l l o a d i n g d i s c ha r g e d i n to

H o n g K o n g w a te r s ( O ve A r u p e t a l . 1 9 8 9 ) . T h e t o t a l

d i s c h a r g e o f P f r o m a f a r m w i t h a p r o d u c t i o n o f 5 0 t

y r - t w o u l d c o r r e s p o n d t o t r e a t e d d i s c h a r g e f r o m 7 0 0 0

p e o p l e , a s s u m i n g 9 0 % o f P is r e m o v e d f r o m t h e

d i s c h a r g e ( H o l b y & H a l l , 1 9 91 ). H o w e v e r , i t s h o u l d b e

n o t e d t h a t f i s h - f a r m w a s t e is n o t d i r e c t l y c o m p a r a b l e t o

d o m e s t i c s e w a g e , m a i n l y b e c a u s e o f d if f e r e n t C : N : P

r a t i o s a n d s i g n i f i c a n t d if f e r e n c e s i n s e t t le a b l e a n d s o l u b l e

w a s t e s ( R o s e n t h a l

e t a L

1988) .

D i s p o s a l o f t h e f o u l in g b i o m a s s o n n e t c a g e s in t o t h e

w a t e r m a y o c c a s i o n a l l y a d d a h i g h p o l l u t i o n l o a d i n g t o

t h e e n v i r o n m e n t . F o r e x a m p l e , t h e f o u l i n g b i o m a s s o n

f is h c a g e s i n H o n g K o n g w a s e s t i m a t e d a t 1 .7 8 t ( w e t

b i o m a s s ) t - l f is h p r o d u c t i o n y r - 1 ( e q u i v a l e n t t o 31 k g

B O D , 7 .5 k g N a n d 7 0 g P ) ( M a k , 1 9 82 ; O v e A r u p e t a l .

1 98 9 ). A l t h o u g h i t m a y b e a r g u e d t h a t n u t r i e n t s a n d

o r g a n i c m a t t e r i n t h e f o u l i n g b i o m a s s m a y b e d e r i v e d

f r o m , a n d r e p r e s e n t p a r t o f , t h e n u t r i e n t s r e le a s e d f r o m

f is h fa r m s , d i s p o s a l o f f o u li n g o r g a n i s m s d u r i n g c a g e

c l e a n i n g w il l a d d a s i g n if i c an t o r g a n i c a n d n u t r i e n t i n p u t

w i t h i n a r e la t i v e ly s h o r t p e r i o d a n d m a y c a u s e p r o b l e m s .

nvironmental Impacts

T h e e n v i r o n m e n t a l i m p a c t o f f is h - fa r m i n g d e p e n d s

v e r y m u c h o n s p ec ie s, c u lt u r e m e t h o d , h y d r o g r a p h y o f

c u l t u r e s it e, f ee d ty p e a n d h u s b a n d r y p r a c t ic e s . A l m o s t

a l l s t ud i e s o n t h e e n v i r o n m e n t a l i m p a c t o f m a r i n e f i sh -

f a r m i n g h a v e b e e n c a r r i e d o u t i n t e m p e r a t e r e g i o n s

w h e r e s a l m o n i d f i s h w e r e c u l t u r e d i n p o n d s / c a g e s a n d

f e d w i t h a r t i f i c i a l f e e d ( G o w e n & B r a d b u r y , 1 9 8 7 ) . O n l y

a s i n g l e s t u d y h a s b e e n c a r r i e d o u t t o a s s e s s t h e

e n v i r o n m e n t a l i m p a c t o f o p e n - w a t e r c a g e f a r m i n g i n

s u b - t r o p i c a l c o n d i t i o n s w h e r e n o n - s a l m o n i d f i s h w e r e

TABLE 1

Ma jor forms and estimated loss of C, N and P to various environmentalcompa rtments and sediment flux in salmonid fish farms (data expressed

as % of total feed input into the system).

2 3 4 5 6

Loss to

environment Net sediment

Fish harvest Loss to water Loss to sediment (2 + 3) Sediment f l u x acc um ulatio n

C

Major form

% 20*

16t

N

Major form

%

P

Major form

20t

24~

% 16~

CO2 from f i s h O rga nic f rom CH4, DOC, CO2 Org anicC

respiration feed wastage and

faecal production

51 29* 80* 6* 23*

4 0 1 4 4 t 8 4 t - - -

A m m o n i a

a nd O r g a n i c f ro m D O N , a m m o n i a O r g a n i cN

urea from fish feed wastage and nitrate and urea

excreta faecal production

52 t 281 80 t 3:~ 211:

51:~ 25:~ 76:~

14-50 II 14-81 II 52-9 5 II

Part iculate and O rga nic from Phosphate Organic P

dissolved P feed wastage and

faecal production

28 56~ 82 3 53

59-66

* Hall e t a l . (1990), estimated by the flux method.

t Gow en & Bradb ury (1987).

:~ Hal l et a l . (1992).

11Hand y & Po xton (1993).

Holby & Ha ll (1991).

E nell (1987).

161


4/8

c u l t u r e d a n d f e d w i th t r a s h f i s h ( W u e t a l . 1994) . The

g e n e r a l p i c tu r e e me r g in g f r o m th e e x i s t i n g s t u d i e s

in d i c a t e s t h a t t h e ma jo r imp a c t i s o n t h e s e a b e d a n d ,

to a le sse r ex ten t , on wa te r qua l i ty .

O r g a n i c ma t t e r s e t t l e d o n t h e s e a b e d ma y l e a d t o

th e d e v e lo p me n t o f a n o x i c a n d r e d u c in g c o n d i t i o n s i n

th e s e d ime n t a n d t h e p r o d u c t i o n o f t o x i c g a s e s (e .g .

a m m o n i a , m e t h a n e a n d h y d r o g e n s u l p h i d e ) . S e d i m e n t

o x y g e n d e m a n d ( S O D ) o f b o t t o m s e d im e n t s e n ri c he d

by f i sh- fa rming ac t iv i t ie s can be some two to f ive t imes

h ig h e r t h a n t h a t o f t h e c o n t r o l s ( W u , 1 9 9 0 a; W u e t a l .

1 9 9 4 ) , w h i l e t o t a l s e d ime n t me ta b o l i s m h a s b e e n

r e p o r t e d a s b e in g 1 0 t ime s h ig h e r t h a n t h a t o f th e

c o n t r o l ( H o lme r & K r i s t e n s e n , 1 9 9 2 ) . C h a n g e s i n

m a c r o b e n t h i c c o m m u n i t y s t r u c t u r e a l o n g a f a r m

w a s t e - e n r i c h e d g r a d i e n t h a v e b e e n d o c u me n te d . A n

a z o i c z o n e w a s t y p i c a l l y f o u n d u n d e r n e a th t h e c a g e s

a n d a d e c r e a s e i n b e n th i c d iv e r s i t y o c c u r r e d i n t h e

v i c in i t y o f t h e f a r m ( R i t z e t a l . 1989; Tsutsumi e t a l .

1 9 9 1 ; W u

e t a l .

1994) . Benth ic a ssemblages were

n o r ma l b e tw e e n 2 5 t o 1 5 0 m a w a y f r o m th e c a g e s i n

w h ic h s a lmo n id s w e r e f e d w i th a r t if ic i al f e e d ( B r o w n e t

a l . 1987; Weston , 1990) whi le the a f fec ted a rea may

e x t e n d t o 1 k m w h e r e t r a s h f i s h a re u s e d a n d f l u sh in g is

p o o r ( W u e t a l . 1994).

C a r b o n d io x id e p r o d u c e d b y f i s h r e s p i r a t i o n i s

u n l i k e ly t o c r e a t e a n y a d v e r s e e f fe c t i n t h e ma r in e

e n v i r o n me n t . U n io n i z e d a m mo n ia i s a c u t e ly t o x i c t o

ma r in e l i f e a n d t o x i c i t y i s d e p e n d e n t u p o n s a l i n i t y ,

t e mp e r a tu r e a n d p H , w h i l e n i t r a t e a n d n i t r i t e a r e n o t

s ign i f ican t ly tox ic to f i sh , except in the contex t of

p r o m o t i n g a l g a l b l o o m s . P h o s p h o r u s i s n o t i m p o r t a n t i n

p r o m o t i n g a l ga l g r o w t h i n t h e m a r i n e e n v i r o n m e n t a n d ,

the re fore , un l ike ly to hav e a s ign i f ican t e f fec t ( for a

r e v ie w , s ee H a n d y & P o x to n , 1 9 93 ).

A d e c r e a s e i n d i s s o lv e d o x y g e n a n d i n c r ea s e s in B O D ,

n u t r i e n t s ( P , o r g a n i c a n d i n o r g a n i c N a n d t o t a l C ) h a v e

b e e n g e n e r a l l y f o u n d i n t h e w a t e r c o lu mn a r o u n d f i s h

f a r ms ( Mu l l e r & V a r a d i , 1 9 8 0 ; B e r g h e im e t a l . 1982;

Bever idge & M uir , 1982; Ene l l, 1982, 1987; Pen czak e t

a l . 1982; Ene l l & Lo f , 1983; Bever idge , 1985; Phi l l ips &

B e v e r id g e 1 9 8 6 ; Mo lv e r e t a l . 1988) . Disso lved oxygen

v a l u e s r e t u r n e d t o n o r m a l 3 0 m a w a y f r o m s a l m o n i d

f a r ms ( G o w e n & B r a d b u r y , 1 9 87 ) b u t a n o x y g e n s a g

ma y e x t e n d t o 1 k m w h e r e t r a s h f i s h i s u s e d a n d c u l t u r e

c o n d i t i o n s a r e p o o r ( W u e t a l . 1994) . Changes in

suspended so l ids , l igh t ex t inc t ion coe f f ic ien t , ch loro-

p h y l l - a a n d p h a e o p ig me n t w e r e c o n s id e r e d t o b e e i t h e r

ins igni f ican t or loca l ized (Bever idge e t a l . 1 9 94 ; W u e t

a l .

1994).

N i t r o g e n i s c o n s id e r e d t o b e t h e l imi t i n g n u t r i e n t f o r

p r ima r y p r o d u c t i o n i n c o a s t a l a r e a s ( G u n d e r s e n , 1 9 8 1 ) .

A m m o n i a a n d u r e a e x c r e te d b y f is h c an b e r e ad i ly t a k e n

u p b y p h y t o p l a n k t o n a n d h e n c e m a y s t i m u l a te t h e ir

g r o w th . I t s h o u ld b e n o t e d t h a t f i s h e x c r e t a a n d w a s t e

f o o d h a v e a N :P r a t i o c lo s e t o 7 :1 w /w ( t h e R e d f i e ld

ra t io) (Aure & S t igebrandt , 1990) , and hence provide

w e l l - b a l a n c e d n u t r i e n t s f o r p h y to p l a n k to n r e q u i r e me n t .

H o w e v e r , i t a p p e a r s u n l i k e ly t h a t ma r in e f i s h - f a r min g

ma y c a u s e e u t r o p h i c a t i o n o n a l a r g e s c a l e , a l t h o u g h t h e

p o s s ib i l i t y o f l o c a l iz e d e u t r o p h i c a t i o n o c c u r r i n g i n a r e a s

o f p o o r f lu s h in g c a n n o t b e e x c lu d e d ( G o w e n &

Marine Pollution ulletin

B r a d b u r y , 1 9 8 7 ; A u r e & S t i g e b r a n d t , 1 9 9 0 ; W u e t a l .

1994).

T h e e n v i r o n m e n ta l e f f e ct s o f p ig me n t s a n d v i t a min s

a r e p o o r ly k n o w n . B io t i n h a s b e e n s h o w n to s t imu la t e

g r o w th o f c e r t ain p h y to p l a n k to n s p e c ie s a n d i s

impl ica ted in the tox ic i ty of the d inof lage l la te G y m n o -

d i n i u m a u r e o l e s ( G o w e n & B r a d b u r y , 1 9 87 ). V i t a min B l2

h a s b e e n s h o w n t o b e o n e o f th e g r o w t h - p r o m o t i n g

f a c to r s o f t h e a lg a C h r y s o c h r o m u l i n a p o l y l e p i s ( w h ic h

c a u s e d m a s s iv e ki ll o f c a g e d c u l t u r e s a lmo n i n

S c a n d in a v i a n w a t e r s ) a n d t h e d in o f l a g e l l a t e H e t e r o -

s i g m a a k a s h i w o (Grane l i e t a l . 1993; Honjo , 1993) . F ish

m e a t a n d f a e c es h a v e b e e n s h o w n to s t imu la t e t h e

g r o w th o f t h e r e d t i d e s p e c i e s G y m n o d i n i u m t y p e 6 5 a n d

C h a t o n e l l a a n t i g u a i n l a b o r a to r y c u l t u r e ( N i s h imu r a ,

1982) . Despi te these labora tory r e su l t s , the re i s no good

sc ien t i f ic ev idence to r e la te the f ie ld occur rence of r ed

t ides to f i sh- fa rm was tes .

T h e u s e o f a n t i b io t i c s i n f i s h f a r ms ma y l e a d t o t h e

d e v e lo p m e n t o f r es i s ta n c e i n b a c t e r i a l p a th o g e n s o f f is h,

a n d t h e p o s s ib i l i t y o f t r a n s f e r o f r e s i s t a n c e t o h u ma n

p a th o g e n s h a s a l s o r a i s e d c o n c e r n ( A o k i , 1 9 8 9 ; D ix o n ,

1 9 9 1 ) . T h e d e v e lo p m e n t o f a r e s i s t a n t b a c t e r i a l

p o p u l a t i o n i n t h e s e d ime n t h a s b e e n d o c u me n te d ( e . g .

Aus t in , 1985; Homer , 1992) . For example , up to 100

o f o x y t e t r a c y c li n e - r e s is t a n t b a c t e r i a h a v e b e e n r e c o r d e d

f r o m ma r in e s e d ime n t n e a r f i s h f a r ms a f t e r me d ic a t i o n ;

a n d r e s i s t a n c e p e r s i s t e d f o r mo r e t h a n 1 3 mo n th s

a f t e r w a r d s ( T o r s v ik e t a l . 1988; Samue lsen e t a l .

1 9 9 2 ) . O n t h e o th e r h a n d , f u r a z o l i d o n e c a n b e r a p id ly

d e g r a d e d b y mic r o b e s a n d h e n c e a n t i b a c t e r i a l a c t i v i ty

w a s n o t d e t e c t a b l e i n s e d ime n t s ( T o r s v ik

e t a l .

1988;

S a mu e l s e n e t a l . 1 9 91 ). I n h ib i t i o n o f s u lp h a t e r e d u c t i o n

in s e d ime n t u n d e r n e a th c a g e s a f t e r a n t i b io t i c t r e a tme n t

has been rep or ted ( IOE, 1992) . The e f fec ts of v i tamins

o n t h e ma r in e e n v i r o n m e n t a r e s ti ll n o t w e l l k n o w n . I n

oxic envi ronm ents , h ow ever , the ha l f- l ives of an t ib io t ic s

and v i tamin s i s shor t ( e .g . < 7 day s in seaw a te r and 32 -

6 4 d a y s i n f i s h - f a r m s e d ime n t s f o r o x y t e t r a c y c l i n e a n d

b io t i n ) ( S a mu e l s e n , 1 9 8 9 ) , a n d t h e a c c u mu la t i o n o f

v i t a min s a n d a n t i b io t i c s i n t h e e n v i r o n me n t i s h ig h ly

u n l ik e ly . A l th o u g h o x y t e t r a c y c l i n e ma y b e v e r y p e r s is t -

en t in anoxic f i sh- fa rm sediments (up to 419 days) , i t i s

n o t b io lo g i c a l l y a v a i l a b l e i n s u c h c a s e s ( B jo e r k lu n d

e t

a l . 1990).

T B T c o n t a min a t i o n h a s b e e n i d e n t i f i e d f r o m th e

t i ssues of cu l ture f i sh (Davies & M cKi e , 1987;

W a ld i c h u c k , 1 9 87 b ), a n d w a t e r ( B a l ls , 1 9 8 7 ; T h r o w e r

& S h o r t , 1 9 9 1 ) w h e r e T B T - t r e a t e d n e t p e n s w e r e u s e d .

H o w e v e r , n o s i g n if i ca n t c h a n g e s i n mo r t a l i t i e s a n d

g r o w th r a t e s w e r e o b s e r v e d i n T B T - c o n t a min a t e d f i s h

( T h r o w e r a n d S h o r t , 1 9 9 1 ) . I mp o s e x h a s a l s o b e e n

r e p o r t e d i n d o g w h e lk s f r o m s e a l o c h s i n S c o t l a n d w h e r e

T B T w a s u s e d i n t r e a t i n g f is h c a g e s ( D a v i e s e t a l . 1987).

D e s p i t e g r o w in g c o n c e r n r e g a r d in g t h e s p r e a d o f

d isease f rom fa rme d f i sh to wi ld s toc k (Hi l l , 1991), the re

h a v e b e e n v e r y f e w d o c u m e n t e d e x a m p l e s . I n m o s t

c a s e s , d i s e a s e i d e n t i f i e d i n o n e p o p u l a t i o n c a n n o t b e

p o s i t i v e ly t r a c e d a s h a v in g s p r e a d f r o m a n o th e r

popula t ion (Bracke t t , 1991) .

C u l tu r e s p e c ie s ma y b e l es s a d a p t a b l e t o t h e n a tu r a l

e n v i r o n me n t , a n d e s c a p e d c u l t u r e f i s h ma y i n t e r - b r e e d

162


5/8

Volume 31/Numbers 4 12/April December 1995

w i th t h e w i ld s t o c k , t h e r e b y a l t e ri n g t h e g e n e p o o l o f t h e

la t te r . However , the re i s insuf f ic ien t ev idence to

a s c e r t a in t h e e c o lo g i c a l imp a c t o f e s c a p e d s t o c k . I t i s

c o n c e iv a b l e t h a t t h e i n t r o d u c e d g e n e in w i ld s t o c k mig h t

b e e l imin a t e d b y n a tu r a l s e l e c ti o n v e r y q u ic k ly .

C o a s t a l h a b i t a t s ( e . g . ma n g r o v e s ) a r e o f t e n d e s t r o y e d

f o r ma r in e f i s h -f a r min g , r e s u l t in g i n t h e l o s s e s o f n u r s e r y

a n d s p a w n in g g r o u n d s f o r ma r in e a n ima l s . C o n f l i c ts

w i th o th e r u s e s o f th e c o a s t a l e n v i r o n me n t ( e. g.

naviga t ion , r ec rea t ion and f i sh ing) and reduc t ions in

c u r r e n t s p e e d h a v e b e e n w e l l d o c u me n te d .

T o w a r d s a S u s t a i n a b l e u t u re

K e e p s t o c k i n g d e n s i t y a n d p o l l u t i o n l o a d i n g s u n d e r

e n v i r o n m e n t a l c a p a c i t y

I t h a s b e e n d e mo n s t r a t e d t h a t e n v i r o n me n ta l imp a c t s

o f ma r in e f i s h -c u l t u re v a r y c o n s id e r a b ly b e tw e e n s i t es

a n d a r e h ig h ly d e p e n d e n t o n w a t e r c i r c u l a t i o n , s t o c k in g

d e n s i t y , h u s b a n d r y p r a c t i c e s a n d f e e d t y p e s ( W u

e t a l .

1 9 94 ). A t o n e s i t e in H o n g K o n g w i th g o o d f lu s h in g a n d

lo w s to c k in g d e n s i t y , b e n th o s ( a n d e v e n c o r a ls ) c o u ld b e

f o u n d u n d e r n e a th c a g e s . T h e r e s u l t s f r o m th i s s t u d y

c lea r ly ind ica ted tha t mar ine f i sh cu l ture can be a

s u s t a in a b l e i n d u s t r y p r o v id e d t h a t s t o c k in g d e n s i t y d o e s

n o t e x c e e d t h e c a r r y in g c a p a c i t y o f t h e w a t e r .

T h e c a r r y in g c a p a c i t y o f th e w a t e r d e p e n d s o n t i d a l

f l us h in g, c u r r e n t a n d a s s imi l at i v e c a p a c i t y o f th e w a t e r

b o d y t o p o l l u ta n t s . O x y g e n c o n s u m p t i o n o f c u l tu r e

s p e c ie s ra n g e s f r o m 8 3 t o > 4 0 0 g 0 2 t - 1 h - 1 ( W u ,

1 9 9 0 b ; Mc L e a n

e t a l .

1993) . Assuming tha t d isso lved

o x y g e n i n s e a w a te r i s 7 mg 0 2 1 - 1 , a t l e a s t 1 7 - 5 7 m 3 o f

f r e s h s e a w a te r w o u ld b e r e q u i r e d t o c o mp e n s a t e f o r t h e

o x y g e n c o n s u m p t io n a lo n e o f 1 t o f c u l tu r e f is h; n o t t o

m e n t i o n t h e a d d i ti o n a l o x y g e n d e m a n d e x e rt e d b y

w a s t e s f r o m th e f a r min g a c t i v i t i e s . I n d e e d , w a t e r u s e

in l a n d - b a s e d r a in b o w t r o u t f a r ms w a s v e r y h ig h

( 2 1 0 0 0 0 - 2 5 2 0 0 0 m 3 t - 1 p r o d u c t i o n ) ( B e v e r id g e

e t a l .

1994) . In open-wa te r cage cu l ture sys tems, i t has been

s u g g e s t e d t h a t a n a n n u a l p r o d u c t i o n o f 2 00 t f is h w o u ld

requi re 1 m 3 s - 1 of cur ren t f low (Terve t , 1981) . In a reas

w h e r e w a t e r e x c h a n g e i s p o o r , t h e f i s h s t o c k s h o u ld b e

reduced .

H a v in g q u a n t i f i e d t h e v a lu e s o f o r g a n i c a n d n u t r i e n t

w a s t e s p r o d u c e d p e r t o n n e o f f is h, a n d d e f in e d

a c c e p t a b l e l imi t s f o r w a t e r a n d s e d ime n t q u a l i t y

p a r a me te r s t o s u p p o r t ma r in e l i f e , t h e ma x imu m

p e r mi s s ib l e s t o c k t h a t t h e d e f i n e d w a t e r / s e d ime n t

q u a l i t y s h o u ld n o t e x c e e d c a n b e e s t ima t e d b y w a t e r

q u a l i t y mo d e l l i n g t e c h n iq u e s . T o t h i s e n d , a n a t t e mp t

h a s b e e n m a d e t o c o n s t r u c t a w a t e r q u a l i t y m o d e l t o

d e t e r min e t h e c a r r y in g c a p a c i t y o f w a t e r i n r e la t i o n t o

c u l t u r e s t o c k a t T h r e e F a t h o m s C o v e , H o n g K o n g ( W u

e t a l . i n p r ep . ) . I n s u m ma r y , t h e mo d e l c o n s i s ts o f 1 . a

2 D , tw o - l a y e r h y d r o d y n a mic mo d e l , t o s imu la t e t i d a l

f l o w s a t a f i sh c u l t u r e s i te , u s in g c o n s e r v a t i o n o f ma s s

e q u a t i o n f o r e a c h l a y e r , a n d 2 . a 3 D ( s e g me n te d a n d

l a y e r e d ) t i d e - a v e r a g e d w a t e r q u a l i t y mo d e l , t o a l l o w f o r

a n a s s e s s me n t o f o r g a n i c a n d n u t r i e n t i n p u t o n t h e

q u a l i t y o f th e r e c e iv in g w a t e r. T h e h y d r o d y n a m ic mo d e l

ca lcu la te s t ida l f low and gene ra te s the necessa ry

h y d r o d y n a m i c i n p u t f o r t he r u n n i n g o f th e w a t e r q u a l it y

mo d e l . T h e w a t e r q u a l i t y mo d e l q u a n t i f i e s t h e r e l a t i o n -

s h ip s b e tw e e n ma jo r b io t i c c o mp o n e n t s ( i . e . b a c t e r i a ,

p h y t o p l a n k t o n , z o o p l a n k t o n , m a c r o a l g a e , b e n t h o s a n d

f ish) and ab io t ic components ( i . e . sa l in i ty , o rganic

c a r b o n , d i s s o lv e d o x y g e n , n i t r o g e n , p h o s p h o r o u s a n d

oxygen) a t a f i sh cu l ture s i te , and a lso desc r ibes the

p r e v a i l i n g ma jo r b io lo g i c a l a n d c h e mic a l p r o c e s s e s

( i n clu d ing o x id a t i o n o f o r g a n i c c a r b o n , n u t r i e n t a n d

p h y t o p l a n k t o n d y n a m i c s , h y d r o l y s i s a n d o x i d a t i o n o f

o r g a n i c a n d i n o r g a n i c N , g r o w th , p h o to s y n th e s i s a n d

r e s p i r at i o n a n d d e c a y o f p l a n t c a r b o n , S O D , f i sh

r e s p i r a t i o n a n d B O D ) . F i s h b io ma s s a n d t h e r e s u l t i n g

p o l l u t a n t s ( o r g a n i c w a s t e a n d n u t r i e n t s ) g e n e r a t e d f r o m

var ious ac t iv i t ie s ( e .g . food was tage , f i sh f aeces and

e x c r e t a , e t c . ) w e r e q u a n t i f i e d a n d i n p u t i n to t h e mo d e l .

B a s e d o n th e i n p u t o r g a n i c a n d n u t r i e n t l o a d in g s f r o m a

g iv e n s t o c k in g d e n s i t y , t h e m o d e l c a l c u l a te s t h e r e s u l ti n g

l ev el s o f N H 3 , N O 2 N O 3 , t o t a l o r g a n i c N , d i s s o lv e d

o x y g e n a n d B O D in t h e r e c e iv in g w a t e r .

T h e r e s u l t s o f t h e s imu la t i o n a r e i n g o o d a g r e e me n t

w i th t h o s e f r o m a f ie l d s t u d y o f th e s a m e s i t e r e p o r t e d

u p o n e a r l i e r ( W u e t a l . 1 9 94 ). B y c o m p a r in g t h e o u t p u t

o f w a t e r q u a l i t y d a t a u n d e r d i f f er e n t s c e n a rio s o f

s tocking dens i ty , the mode l can se rve a s an e f fec t ive

t o o l t o h e lp m a n a g e m e n t d e c i s i o ns o n t h e m a x i m u m f is h

s tock pe rmiss ib le a t a pa r t icu la r f i sh cu l ture s i te so tha t

a c c e p t a b l e w a t e r q u a l i t y o b j e c t i v e s c a n b e me t f o r t h e

s u s t a in a b l e d e v e lo p me n t o f t h e i n d u s t r y .

I m p r o v e d a r t if i ci a l f e e d f o r m u l a t i o n

A b o u t 8 0 - 8 4 o f C , 5 2 - 9 5 o f N a n d 8 2 o f P i n

f e e d i n p u t t o t h e c u l t u r e s y s t e m ma y b e l o s t t h r o u g h f e e d

w a s t a g e s , e x c r e t io n a n d f a e c a l p r o d u c t i o n ( T a b l e 1 ), a n d

s u c h l o s s e s c a n b e min imiz e d b y imp r o v e d f e e d

t e c h n o lo g y .

F e e d w a s t a g e c a n b e r e d u c e d b y i n c r e a s in g t h e

s tab i l i ty and reduc ing the s ink ing ra te of f eed , and

provid ing the f i sh wi th an o pt im a l s ize of f eed a t

d i f fe r e n t s t a g es o f d e v e lo p m e n t . A m m o n ia e x c r e t i o n b y

f is h i s a f u n c t i o n o f p r o t e in i n t a k e a n d c a n b e k e p t t o a

min imu m; w i th a h ig h ly d ig e s t i b l e f e e d a n o p t ima l

p r o t e in / e n e r g y r a t i o c a n b e p r o v id e d f o r e a c h s p e c i e s

a n d i t s d e v e lo p me n ta l s t a g e s . T h e e n e r g y r e q u i r e me n t s

o f fi s h c a n b e s a t i sf i ed b y c a r b o h y d r a t e s a n d f a t , s o t h a t

p r o t e in c a n b e s p a r e d f o r b o d y t i s s u e c o n s t r u c t i o n . I t

h a s b e e n s h o w n th a t p r o t e in r e t e n t i o n i n S p a r u s a u r a t a

c a n b e i n c r ea s e d f r o m 2 4 .3 t o 3 1 . 3 b y in c r e a s in g t h e

die ta ry l ip id by 37 (Kiss i l & Lu pa ts ch , 1992) .

O b v io u s ly , r e d u c t i o n o f N in t h e d i e t c a n o n ly b e

achieved i f a r t i f ic ia l f eed i s used . There i s l i t t l e doubt

tha t formula ted a r t i f ic ia l f eed i s supe r ior to t r a sh f i sh , in

t e r ms o f i ts n u t r i ti o n a l v a lu e , s t o ra g e , s u p p ly a n d

pol lu t ion loading . The reason tha t t r a sh f i sh i s s t i l l

w id e ly u s e d in A s i a (e .g . J a p a n , H o n g K o n g , S in g a p o r e

a n d T h a i l a n d ) a p p e a r s t o b e l a r g e ly d u e t o o u r p o o r

u n d e r s t a n d in g o f th e n u t r i ti o n a l r e q u i r e me n t s o f t h e

v a r io u s n o n - s a lm o n id s p e c ie s c u l t u r e d . T h i s p o in t s t o

th e u r g e n t n e e d f o r r e s e a r c h i n to t h e n u t r i t i o n a l

r e q u i r e me n t s o f th e s e n o n - s a lmo n id s p e ci e s.

Mo r e r e c e n t l y , a t t e mp t s h a v e b e e n ma d e t o min imiz e

f e e d u s a g e b y v i d e o m o n i t o r i n g o f f e e d b e h a v i o u r

163


6/8

( G u l d b e r g e t a l . , 1 9 9 3 ) o r i n s t a l l a t i o n o f f e e d i n g d e v i c e s

w i t h a h y d r o a c o u s t i c s e n s o r ( J u e ll , 1 9 9 1 ).

Ma rine Pollution Bulletin

l e a d t o t h e r e le a s e o f o r g a n i c m a t t e r a n d n u t r i e n t s i n t h e

s e d i m e n t , t h i s o p t i o n s h o u l d b e t r e a t e d w i t h c a u t i o n .

H a r v e s t p o l l u t a n t s b y i n t e g r a t e d c u l t u r e

M a r i n e m a c r o a l g a e c a n t a k e u p N , w h e r e a s f i l t e r -

f e e d e r s ( e . g . b i v a l v e s ) c a n r e m o v e p a r t i c u l a t e a n d

p h y t o p l a n k t o n f r o m w a t e r a t re m a r k a b l e r a te s . H a r v e s t -

i n g n u t r i e n t s g e n e r a t e d b y m a r i n e f i s h - f a r m i n g b y

m a c r o a l g a e a n d f i l t e r- f e e d e r s w o u l d b e a n a t t r a c t i v e

o p t i o n s i n c e t h i s w o u l d a l l e v i a t e n u t r i e n t p o l l u t i o n o n

o n e h a n d a n d i n c re a s e p r o d u c t i v i ty o n t h e o t h e r .

U p t a k e o f a m m o n i a , t is s ue N c o n t e n t a n d y i e l d o f th e

g r e e n a l g a U l v a l a c t u c a i s l i n e a r w i t h r e s p e c t t o a m b i e n t

c o n c e n t r a t i o n ( H o , 1 9 9 3 ). It h a s b e e n s h o w n t h a t 1 k g o f

U. l ac tuca c a n r e m o v e 9 0 o f a m m o n i a c a l n i t ro g e n i n

e f f lu e n t s p r o d u c e d b y 7 5 k g o f fi sh a n d g i v e a m a x i m u m

y i e l d o f 5 5 g m - 2 d - 1 d r y w t i n a l a n d - b a s e d f is h f a r m

( C o h e n & N e o r i , 1 9 9 1 ; N e o r i et a l . , 1991) . S i mi l a r l y ,

c u l t u r i n g b r o w n m a c r o a l g a e L a m i n a r i a a n d M a c r o -

cys t i s ) n e a r f i s h f a r m s f o r n u t r i e n t r e m o v a l w a s

c o n s i d e r e d t o b e b o t h e c o n o m i c a l l y a n d t e c h ni c a ll y

f e a s i b l e b y P e t r e l l et a l . ( 1 9 9 3 ) . A n i n c r e a s e i n f i s h y i e l d

( b y 1 . 5 ) a n d d i s s o l v e d o x y g e n ( b y 9 ) h a v e b e e n

r e p o r t e d f r o m a J a p a n e s e o p e n - c a g e c u lt u r e s ys t e m

c o n s i s t in g o f r e d s e a b r e a m a n d s e a le t t u c e (A n o n . ,

1994) .

T h e f i l te r i n g ra t e s o f t h e o y s t e r Crassos t rea g igas a n d

t h e s c a l l o p P a t i p e c t i n y e s s o e n s i s m a y b e u p t o 1 01 a n d

9 5 1 d - 1 i n d i v i d u a l - a , r e s p e c t i v e ly ( I n u i et a l . , 1991) . In -

s i tu c l e a r a n c e r a t e s o f m u s s e l b e d s r a n g e d f r o m 0 . 4 t o

2 . 7 m 3 m - 2 h - 1 ( P r i n s et a l . , 1994) . Smal l & Pr i ns (1993)

e s t i m a t e d t h a t t h e u p t a k e r a t e s o f s u s p e n d e d p a r t i c u l a t e

m a t t e r ( S P M ) , p a r t ic u l a t e o r g a n i c c a r b o n ( P O C ) a n d

p a r t i c u la t e o r g a n i c n i t r o g e n ( P O N ) b y n a t u r a l o y s t e r /

m u s s e l b e d s w e r e v e r y h i g h a t 8 1 - 2 8 0 0 g S P M , 4 . 6 - 1 8 6 . 5

g P O C a n d 0 . 6 -3 3 . 6 g P O N m - 2 d - 1 , r e sp e c ti v el y . T h e

u s e o f m u s s e l /o y s t e r b e d s t o c o n t r o l p h y t o p l a n k t o n

g r o w t h a n d e u t r o p h i c a t i o n h a s b e e n s u g g e s t e d b y

C l o e r n ( 1 9 8 2 ) a n d L o o & R o s e n b e r g ( 1 9 8 9 ) . R e c e n t l y ,

S h p i g e l et a l . ( 19 9 3) d e m o n s t r a t e d th a t s o m e 6 3 o f N

i n t h e f e e d c a n b e h a r v e s t e d i n a n i n t e g r a t e d l a n d - b a s e d

c u l t u re s y s te m c o m p o s e d o f b i va l ve s C r a s s o s t r e a g i g a s

a n d T a p e s s e m i d e c u s s a t u s ) a n d s e a w e e d Ulva l ac tuca )

( 2 6 a s f i s h y i e l d , 1 4 . 5 a s b i v a l v e y i e l d a n d 2 2 . 4 a s

s e a w e e d y i e l d ) . C o m p a r e d w i t h a ' m o n o c u l t u r e ' f i s h

f a r m i n w h i c h 8 0 o f N i n p u t w i ll b e l o s t ( G o w e n &

B r a d b u r y , 1 9 8 7 ), o n l y 3 7 o f N i n p u t w a s l o s t i n t o t h e

e n v i r o n m e n t i n t h i s i n t e g r a t e d c u l t u r e s y s t e m . C u l t u r i n g

s h e ll fi sh t o r e m o v e N a n d p l a n k t o n p r o d u c t i o n d e r i v e d

f r o m f i s h - f a r m p o l l u t i o n a p p e a r s t o b e a v i a b l e a n d

p r a c t ic a l o p t i o n a n d s h o u l d b e a d a p t e d t o o p e n - c a g e

c u l t u r e s y s te m s . H o w e v e r , c a u t i o n m u s t b e e x e r c is e d t o

a v o i d b a c t e r i a l c o n t a m i n a t i o n o f s h e l l f i s h f r o m f i s h

f a r m s .

M u d c o n s u m p t i o n o f m a n y b o t t o m d e p o s it - fe e d e r s is

h i gh . F o r e x a m p l e , m u d c o n s u m p t i o n b y t h e se a

c u c u m b e r r a n g e d f r o m 4 4 1 g t o 3 . 5 k g i n d i v i d u a l - l

y r - 1 ( O n g C h e , 1 9 90 ; In u i et a l . , 1 9 9 1 ) . T h e p o s s i b i l i t y

o f c u l t u r i n g b o t t o m d e p o s i t - f e e d e r s ( e. g . p o l y c h a e t e s ,

h o l o t h u r i a n s ) t o r e m o v e o r g a n i c d e p o s i t s s h o u l d b e

e x p l o re d . H o w e v e r , s in c e b i o t u r b a t io n o f s e d im e n t m a y

E n v i r o n m e n t a l i m p a c t a s s e s s m e n t , m o n i t o r i n g a n d

c o n t r o l

W h i l e e n v i r o n m e n t a l i m p a c t a s s e s s m e n t ( E I A ) t e n d s

t o b e c o m e a s t a n d a r d r e q u i r e m e n t f o r m a j o r d e v e l o p -

m e n t a l p r o j e c t s n o w a d a y s , t h e a p p l i c a t i o n t o m a r i n e

f i s h - fa r m i n g is m u c h l e s s c o m m o n . I n d e e d , E I A h e l p s to

p r e v e n t c o n f l i c t b e t w e e n c o a s t a l u s e r s , p r o t e c t s s e n s it iv e

h a b i t a t s a n d i s i m p o r t a n t f o r s u s t a i n a b le d e v e l o p m e n t

o f th e m a r i c u l t u r e i n d u s t r y . S i n c e n i t r o g e n a n d o r g a n i c

w a s t e s a r e m a j o r c o n c e r n s , t h e s u s c e p t i b il i ty o f t h e s it e

t o d i s so l v e d o x y g e n c h a n g e s a n d n i t r o g e n p o l l u t i o n

s h o u l d b e g i v e n s p e ci a l a t t e n t i o n i n a n y E I A o f m a r i n e

f i s h - f a r m i n g .

E f f l u e n t s t a n d a r d s f o r l a n d - b a s e d f i s h f a r m s h a v e b e e n

w e l l e s t a b l i s h e d ( e . g . A l a b a s t e r , 1 9 8 2 ) . I t w o u l d ,

h o w e v e r , b e m u c h m o r e d i ff ic u l t t o s e t e f f lu e n t s ta n d a r d s

a n d c o n t r o l e f f l u en t q u a l i t y in o p e n - w a t e r c a g e f a r m i n g

s y s te m s . F o r e x a m p l e , i n s u ff i ci e n t i n f o r m a t i o n i s

a v a i l a b l e o n e f f l u e n t t o x i c i t y i n s e a w a t e r t o a l l o w

e n v i r o n m e n t a l s t a n d a r d s f o r N t o b e s e t ( H a n d y &

P o x t o n , 1 9 93 ). I t a p p e a r s t h a t t h e m o s t p r a c t i c a l w a y t o

c o n t r o l p o l l u t i o n f r o m o p e n - c a g e f a r m i n g w o u l d b e t o

c o n t r o l t h e s t o c k i n g d e n s i t y i n r e l a t i o n t o t h e c a r r y i n g

c a p a c i t y o f th e r e c e i v in g w a t e r . R e g u l a r m o n i t o r i n g o f

w a t e r a n d s e d i m e n t q u a l i t y a t f i s h c u l t u r e s i t e s w o u l d

a l s o b e r e q u i r e d , a n d i n d e e d , b e c o m e s m a n d a t o r y i n

s o m e c o u n t r i e s ( H e n s e y , 1 9 9 2 ) .

I n s u m m a r y , m a r i n e f i s h - f a r m i n g c a n b e a s u s t a i n -

a b l e d e v e l o p m e n t , a n d m a y s e r v e a s a n e n v i r o n m e n t a l

p r o b e t o d e t e c t c o a s t a l p o l l u t i o n a n d p r o t e c t m a r i n e

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