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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
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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.)
160
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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
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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
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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
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( 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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