Gomiero_Biodiversity_China-Italy_AGEE_1997

8/7/2019 Gomiero_Biodiversity_China-Italy_AGEE_1997

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ELSEVIER Agriculture, Ecosystems and Environment 62 (1997) 169-185

A g r i c u l t u r eE c o s y s t e m s &E n v i r o n m e n t

Bi od i ve r s i ty u s e an d te c h n i c a l p e r for m an c e o f f r e s h w at e r f is haquacul ture in d i f ferent soc ioeconomic contexts : China and I ta ly

Tiz iano G om iero a, M ar io Giampie tro b , * , Sandra G.F. Bukkens a , bMau r i z i o G . P ao l e t t i a

a Depar tmen t o f B io logy Univers i~ o fPado va , Padova , I ta lyb ls t i tuto Nazio nale della Nutrizione, Via Ardea tina 546, 0017 8 Rome, I taly

A b s t r a c t

T h e a v a i l a b i l i ty o f n a t u r a l r e s o u r c e s a n d t h e s o c i o e c o n o m i c co n t e x t i n w h i c h a q u a c u l t u re i s p e r f o r m e d c o n d i t i o n t h echo ice o f aquacu l tu ra l p roduc t ion t echn iques . In th i s pape r , we exam ine and com pare the pa t t e rn o f b iod ive rs i ty use ( theeco log ica l s ide o f the p roduc t ion p roces s ) and the t echn ica l coe f f i c ien t s ( the econom ic s ide o f the p roces s ) tha t cha rac te r i zef re shwa te r aquacu l tu re in PR China and in I t a ly in re la t ion to the ro le tha t f re shwa te r aquacu l tu re p lays in these soc ie t i e s .The com par i son be tween aquacu l tu re in China and I t a ly cove rs the fo l lowing a spec t s : (1 ) h i s to ry and gene ra l s t a t i s t i c s o faquacu l tu re ; (2 ) cu l t iva ted spec ie s and t roph ic s t ruc tu re o f m anaged f re shwa te r ecosys tem s ; (3 ) t echno log ica l cha rac te r i s t i c so f t h e p r o d u c t i o n p r o c e s s , i n c lu d i n g i n p u t s / o u t p u t s , y i e l d s , l a b o r p r o d u c t i v i ty , a n d f o s s i l e n e r g y u s e ; ( 4 ) r o l e o f f r e s h w a t e raquacu l tu re in re la t ion to i t s soc ioeconom ic con tex t .

In I t a ly , where soc ioeconom ic cons t ra in t s (h igh oppor tun i ty cos t o f l abor and a food sys tem dea l ing wi th a su rp lus o fnu t r i en t s ) ove rwhe lm eco log ica l cons t ra in t s ( th rough im por t s and t echno logy) , f re shwa te r aquacu l tu re ope ra te s wi th dens i t i e so f nu t r i en t f lows ou t s ide the range typ ica l o f na tu ra l aqua t i c ecosys tem s . Fre shw a te r bod ie s used fo r p rodu c t ion a re a r t i f i c ia la n d g e n e r a l l y c o n t a i n o n l y o n e c a r n i v o r o u s s p e c i es t h a t d e p e n d s f o r i ts s u r v i v a l o n h u m a n m a n a g e m e n t o f i n p u t s a n d w a s t ed i sposa l .

In con t ra s t , in China , u p to n ine d i f fe ren t spec ie s (m a in ly he rb ivores ) a re kep t in the s am e po nd , and e f fo r t s a re m ade tom a i n t a i n a s m u c h a s p o s s i b l e t h e n a t u r a l m e c h a n i s m s o f r e g u l a t i o n o f m a t t e r a n d e n e r g y f l o w s . T h i s r e s u l t s i n h i g h e re f f i c ie n c y i n t e r m s o f u s e o f b i o l o g i c a l e n e r g y ( f r o m b i o l o g i c a l c y c l e s ) w i t h in t h e s y s te m , l o w e r e n v i r o n m e n t a l l o a d i n g , a n dle s s dependen ce on fos s i l ene rgy inpu t s . How ever , the be t t e r b iophys ica l pe r fo rm ance o f Chinese aq uacu l tu re i s l inked tolow labor p roduc t iv i ty . Th i s m akes i t d i f f i cu l t to adop t such an ' e c o log ica l ly f r i end ly ' so lu t ion in deve loped coun t r i e s , suchas I t a ly , where the oppor tun i ty cos t o f l abor i s h igh . 1997 E ls ev ie r Sc ience B . V.Keywords: Aquaculture; Biodiversity; Productivity; Freshwater fisheries; Labour; Environm ent; China; Italy

1 . I n t r o d u c t i o nA q u a c u l t u r e i s g e n e r a l l y d e f i n e d a s t h e f a r m i n g o f

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

* Corresponding author. Tel: 39 6 503 2 421 ; fax: 39 6 5031592; e-mail: [email protected].

t a c e a n s a n d a q u a t i c p l a n t s , w h e r e f a r m i n g i n d i c a t e ss o m e f o r m o f i n t e r v e n t i o n i n t h e r e a r i n g p r o c e s s t oe n h a n c e p r o d u c t i o n , s u c h a s s t o c k i n g , f e e d i n g , a n dp r o t e c t i o n f r o m p r e d a t o r s ( M u i r , 1 9 9 0 ; P u l l i n , 1 9 9 3 ;F A O , 1 9 9 5 ) .

F i s h a q u a c u l t u r e c a n b e b r o a d l y c l a s s i f i e d i n t ot h r e e t y p e s ( M i l s t e i n , 1 9 9 2 ; D e M u r t a s , 1 9 9 3 ; P u l l i n ,

0167-8809/97/$17.00 1997 Elsevier Science B.V. All rights reserved.P II SO 1 6 7 - 8 8 0 9 ( 9 6 ) 0 1 l 3 6 - X


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170 T . G o m i e r o e t al . / A g r i c u l t u r e , E c o s y s t e m s a n d E m ; i r o n m e n t 6 2 ( 1 9 9 7 ) 1 6 9 - 1 8 5

1993) . (1 ) Ex t e ns i ve a qua c u l t u re , whe re f i she s a rel i gh t l y s t oc ke d . Ex t e ns i ve a qua c u l t u re doe s no t r e l yon fe e d o r f e r t i l i z e r i npu t s ; no r do e s i t boos t t hewa t e r t h roughpu t . As a c onse que nc e , i t i s c ha ra c t e r -i z e d by re l a t i ve l y l ow y i e l d s a nd l ow p roduc t i onc os t s . (2 ) S e mi - i n t e ns i ve a qua c u l t u re , whe re na t u ra lp roduc t i on i s s t i mu l a t e d t h rough l i mi t e d a moun t s o ff e r ti l iz e r i n p u t a n d / o r o r g a n i c m a n u r in g . A l s o l i m -i t e d a moun t s o f f e e d ma y be supp l i e d t o i n t e g ra t ea va i l a b l e na t u ra l food . (3 ) In t e ns i ve a qua c u l t u re ,whe re f i she s a re de nse l y s t oc ke d . In t e ns i ve a qua c u l -t u re i s l a rge l y r e l i a n t on fe e d i npu t a nd ba se d on awa t e r t h roughpu t t ha t i s ke p t a r t i f i c i a l l y h i gh . As ac onse que nc e , i n t e ns i ve a qua c u l t u re ha s h i gh y i e l d sa n d h i g h p r o d u c t i o n c o s t s . R e c e n t d e v e l o p m e n t s i nwa t e r r e c i r c u l a t i on sys t e ms , i nc re a s i ng l y a dop t e d i nt he US A, c a n , howe ve r , g re a t l y r e duc e wa t e r c on -s u m p t i o n a n d i n c r e a s e t h e o u t p u t / i n p u t c o n v e r s i o nra t io .

In s e mi - i n t e ns i ve a qua c u l t u re , t he r a t i o be t we e nf i sh b i oma ss ou t pu t ( i n kg ) a nd fe e d i npu t ( i n kg ) i sg re a t e r t ha n 1 , whe re a s i n i n t e ns i ve sys t e ms t h i s r a t i oi s sma l l e r t ha n 1 . Mui r (1990) e s t i ma t e s t he fo l l ow-i ng c onve rs i ons : fo r s e mi - i n t e ns i ve sys t e ms , t he p ro -duc t i on o f 100 tons o f b i oma ss r e qu i re s a bou t 39t ons o f f e e d (30 t ons food a nd 9 t ons f i shme a l ) wi t ha n o u t p u t / i n p u t r a t i o o f 2 .5 6 ; f o r i n t en s i v e s y s te m s ,100 tons o f p roduc e d f i sh c a n re qu i re up t o 260 t onso f f e e ds (180 t ons food a nd 80 t ons f i shme a l ) wi t ha n o u t p u t / i n p u t r a t i o o f 0 . 3 8 .

In t e ns i f i c a t i on o f f i sh f a rmi ng i mp l i e s t ha t t here gu l a t i on o f f l ows o f ma t t e r a nd e ne rgy i s pu t unde rhuma n c on t ro l . In i ndus t r i a l f i sh f a rms , wa t e r be -c ome s a me re phys i c a l suppor t fo r f i she s , a l i me n t a -t i on re l i e s on c on t ro l l e d ou t s i de supp l i e s o f a r t if i c ia lf e e d , a nd oxyge n supp l y a nd wa s t e d i sposa l a rer e g u l a t e d b y m e c h a n i c a l p o w e r ( B a r d a c h , 1 9 8 6 ;Ba rna b6 , 1991) . S t oc k i ng de ns i t y i n c a ge s fo r i n -c r e as i n g f is h b o d y w e i g h t is h ig h , u p t o 2 5 - 5 0 k g o ff i nge r l i ngs pe r c ub i c me t re o f wa t e r , de pe nd i ng onthe spec ies (Barnab6, 1991) .

A q u a c u l t u r e o f f i s h a n d o t h e r o r g a n i sm s ( m o l -luscs , c rus taceans , aqua t ic p lants , e tc . ) i s ca rr ied oute i the r in in land fac i l i t i e s , such as lakes , a r t i f ic ia lpon ds , and tanks , or in coas ta l a reas of the sea , suchas cages and other enc losures (Barnab6, 1990) . In1993 , i n l a nd a qua c u l t u re a c c oun t e d fo r 66% o f t o t a lwor l d a qua c u l t u re p roduc t i on (F AO, 1995) (F i g .

( a )M a r i n e5,560,000 ton(34 %1

I n l a n d10,730,00(I ton(66 %)

{ b ) F o . . . . . U S S R 1 . 1 %South ,

North A m eEurope

2hina 45.0 %

Other Asiat icCoun t r i e s4 0 . 8 ~

F i g . 1 . ( a ) W o r l d a q u a c u l t u r e p r o d u c t i o n i n 1 9 9 3 ( s o u r c e F A O ,1 9 95 ). ( b ) A q u a c u l t u r e p r o d u c t i o n b y c o n t i n e n t ( s o u r c e F A O ,1995).

l ( a ) ) . As i a t i c a qua c u l t u re a c c oun t s fo r 85 .8% o f t het o t a l wor l d p roduc t i on , wh i l e Europe a n a qua c u l t u re ,s e c ond i n i mpor t a nc e , fo l l ows fa r be h i nd wi t h 7 .3%of t he to t a l p roduc t i on (F AO, 1995) (F i g . l (b ) ) .

In the 1980s , f reshwate r f i sh aquacul ture under-we n t d ra ma t i c g rowt h , wh i c h wa s ge ne ra t e d by t wofa c t o r s : a g l oba l i nc re a se i n t he p roduc t i on o f someh i gh -va l ue d spe c i e s , a nd a ge ne ra l i n t e ns i f i c a t i on o fp roduc t i on i n Ch i na (Al e xa ndra t os , 1995) . In f a c t ,f r e shwa t e r f i sh c u l t u re ha s g rown f rom 4 .5 mi l l i ontons in 1983 to 10.7 mi l l ion tons in 1993 (FAO ,1995) . In t he l a s t f e w ye a r s , Ch i na ha s a c c oun t e d fo ra bou t ha l f o f t he t o t a l wor l d p roduc t i on (Al e xa ndra -t o s , 1995) (F i g . l (b ) ) .

F i sh r e p re se n t s a mi nor sou rc e o f e ne rgy supp l yi n t he a ve ra ge huma n d i e t . F o r i n s t a nc e , i n de ve l op -i ng c oun t r ie s , on a ve ra ge , on l y 17 ou t o f 2475 kc a lc onsume d pe r c a p i t a pe r da y (a bou t 1% ) a re f romf i sh (Al e xa ndra t os , 1995) . Howe ve r , f i sh i s a goodsourc e o f e s se n ti a l a m i noa c i ds , f a t t y a c i ds, v i t a mi ns ,


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T. Gom iero et al. / Agriculture, Ecosystems and Environment 62 (1997) 169-185 171a nd mi ne ra l s (Al e xa ndra t os , 1995) . In muc h o f As i aa nd Af r i c a , f i sh i s a n i mpor t a n t sou rc e o f h i gh -qua l -i t y a n i ma l p ro t e i n (P u l l i n , 1993) .

In t h i s pa pe r , we e xa mi ne t he l i nk be t we e n t hes o c i o e c o n o m i c c o n t e x t i n w h i c h f r e s h w a t e r f i s ha q u a c u l t u r e i s p e r f o r m e d a n d t h e c h o i c e o f p r o d u c -t i on t e c hn i que s , by c ompa r i ng a qua c u l t u re i n t wowi de l y d i f f e re n t soc i e t i e s , I t a l y a nd P R Ch i na . W i t hre ga rd t o p roduc t i on t e c hn i que s , we e xa mi ne t het e c hn i c a l c oe f f i c i e n t s c ha ra c t e r i z ing a q ua c u l t u re p ro -duc t i on ( l i nke d t o t he e c onomi c s i de o f t he p roduc -t i on p roc e s s ) a s w e l l a s t he pa t t e rn o f b i od i ve r s i t yuse ( t he e c o l og i c a l s i de o f t he p roduc t i on p roc e s s ) .

2 . His tory an d gen era l ch aracter i s t i c s o f f res h w a-ter f i s h aq u acu l tu re in PR C h in a an d I ta ly2 . 1 . P R C h i n a

Ac c ord i ng t o h i s t o r i c a l doc ume n t s , a r t i f i c i a l f i shponds i n Ch i na we re dug a s e a r l y a s 1142 BC (Zha o ,1 99 4) . D u r i n g t h e W e s t e r n Z h o u D y n a s t y ( 1 0 6 6 - 7 7 1BC) t he re mos t l i ke l y wa s a l r e a dy some k i nd o ff i she ry ma na ge me n t , a s i s sugge s t e d by t he ru l e s onf i she ry e xp l o i t a t i on e x i s t i ng a t t ha t t i me . The Ch i -ne se ph i l o sophe r Me nc i us , l i v i ng a t t ha t t i me , wro t e"Do no t c a s t t oo ma ny ne t s i n a sma l l pond , fo r f i sha nd t u r t l e shou l d no t be ove r - f i she d" (F AO, 1980a )- - a n e a r l y e xa mpl e o f a c a ll fo r sust a ina b l e f ishe r i e s.Th e t r e a t is e on p i s c i c u l t u re F i s h B r e e d i n g , da t e d 475BC a nd a sc r i be d t o F a n L i , de a l s wi t h t he spa wni ngof c a p t i ve c a rp , a nd p rove s t ha t f i sh f a rmi ng wa swi de l y p ra c t i c e d i n Ch i na a t t ha t t i me (Borge se ,1980; FAO, 1980a ,b; Zhong, 1992; Li and Mathias ,1994).

I n t h e b e g i n n i n g o f t h e T a n g D y n a s t y ( 6 1 8 - 9 0 7AD) , c a t c h i ng , s e l l i ng a nd e a t i ng c ommon c a rp wa sb a n n e d b e c a u s e t h e p r o n u n c i a ti o n o f t he w o r d ' c o m -mon c a rp ' ( ' L i ' i n Ch i ne se ) sounde d l i ke t he e m-p e r o r ' s n a m e . A s a c o n s e q u e n c e , t h e C h i n e s e p e o p l et u rne d t o t he e xp l o i t a t i on o f o t he r spe c i e s . As wi l df ry o f o t he r spe c i e s o f c a rp i n Ch i na we re a bunda n ta nd e a s i l y f i she d i n t he Ya ng t z e a nd P e a r l r i ve r s ,such as grass ca rp ( C t e n o p h a r y n g o d o n i d e l l e ) , b l a c kc a rp ( M y l o p h a ~ n g o d o n p i ce u s ), s i l ve r c a rp ( H y p o -p h t h a l m i c h t h y s m o l i t r i x ) , a n d b i g h e a d c a r p( A r i s t i c h t h y s n o b i l i s ) , t h e y q u i c k l y b e c a m e p o p u l a r

a nd we re r e a re d t oge t he r i n ponds . Monoc u l t u re o ft h e c o m m o n c a r p w a s t h u s r e p l a c e d b y p o l y c u l t u r eo f o t he r c arp spe c i e s (F AO , 1980a ; L i , 1992 ; Zhong ,1992; Li and Mathias , 1994) .

Unt i l about 1960, f i sh cul ture ac t iv i t ie s remainedde pe nde n t on t he sou rc e s o f e ggs a nd f i nge r l i ngsf rom na t u ra l wa t e r bod i e s i n t he Ya ng t z e a nd P e a r lr i ve r va l le ys a nd a re a s c l o se ne a rby . In t he 1960s ,a r t if i c ia l spa wni ng o f t he c a rp f a m i l y wa s f i r s t de ve l -ope d a nd b rough t i n t o u se , i n t h i s wa y wi de l y e x -t e nd i ng a nd i mprov i ng f i sh c u l t u re i n Ch i na (F AO,1980a ,b) .

The ye a r l y f r e shwa t e r f i sh p roduc t i on ha s be e ni nc re a s i ng sha rp l y i n Ch i na : f rom 500 t housa nd t onsin 1936 to 1 mi l l ion tons in 1957, to 2 mi l l ion tons in1984, and to 4 .2 m i l l ion tons in 1990 (of which 3 .3mi l l i on tons w e re f rom pond f i she r ie s ) (Zhong , 1992 ;F AO , 1993). P roduc t i on o f t o t al f r e shwa t e r f ishreached 6 .5 mi l l ion tons in 1993 (FAO, 1995) (F ig .2(a )) .

S ince the 1980s , C hina has been the la rges t pro-duc e r o f i n l a nd f i she r i e s a nd a qua c u l t u re ou t pu t .S i nc e 1990 , i t ha s a l so be e n t he l a rge s t f i sh p rod uc e ri n t he wor l d i n t e rms o f t o t a l p roduc t i on . P o l i c yre fo rms t ha t we re i mp l e me n t e d i n t he c oun t ry du r i ngt he 1980s ha v e be e n e f fe c t i ve in e nha nc i ng t he u t i -l i z a t i on o f e x i s t i ng re sou rc e s a nd re su l t e d i n a sub -s tant ia l inc rease in y ie lds (FAO , 1980a , 1993; Smi l ,1985 ; F AO , 1989 ; P R Ch i na MA BF , 1995). Ne ve r -the less , to da te f i sher ies a re s t i l l a negl ig ib le sec toro f Ch i na ' s a g r i c u l t u re , a c c oun t i ng fo r l e s s t ha n 2%of t he t o t a l va l ue o f a g r i c u l t u ra l p roduc t i on (Zha o ,1994).

F i sh c u l t u re i n Ch i na i s p ra c t i c e d i n a ny k i nd o fi n l a nd a qua t i c e nv i ronme n t , i nc l ud i ng ponds , l a ke s ,rese rvo i rs , and r ive rs (FA O, 1980a , 1993; Zha o,1994 ; P R Ch i na MA, 1995 ; P R Ch i na MABF , 1995) .Among t he se wa t e r bod i e s , pond f i sh c u l t u re ha s t heh i ghe s t p roduc t i v i t y , wi t h a n a ve ra ge p roduc t i on o fa bou t 2400 kg ha -~ i n 1990 (F AO, 1993 ; Qi a n ,1994) (Table 1) . As noted ea r l ie r , China ' s aquacul -t u re p roduc t i on a c c oun t s fo r a l mos t ha l f t he t o t a lwor l d p roduc t i on , a nd ha l f o f t he Ch i ne se p roduc t i oni s f rom i n l a nd c u l t u re o f f r e shwa t e r f i sh . Ch i ne sec a rp a c c oun t fo r a bou t 80% o f th i s (F AO , 1995).

Ac c ord i ng t o t he Mi n i s t ry o f Agr i c u l t u re (P RChi na MA, 1995) , Ch i na ha s 6 .75 mi l l i on ha o fin land wate r su i table for f i sh fa rming. In 1994, aqua-


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17 2 T . Gorn iero e t al . / Agr icu l tu re , Ecosys tem s and Env iro nme n t 62 (1997 ) 16 9 -1 85( a ) 8 -

( b ) 1 20

1O0

80260

Ill China 1964 t

m a r m e c r u s t a c e a n s m o l l u s c s a q ua ti c f r e s h w a t e rf i s h e s p l a n t f i s h e s

[] Italy 1984[] hal y 1993

2O

0c r u s t a c e a n s a q u a t i cp l a n t m a r i n e f r e sw a t e r m o l l u s c sf i s h e s f i s h e sF ig . 2 . ( a ) Aquacu l tu re p roduc t ion in PR C h ina in 1984 and 1993(sou rce FAO , 1995) . (b ) Aqua cu l tu re p roduc t ion in I ta ly in 1984and 1993 ( sou rce FAO , 1995).

cu l tu re was p rac t i ced in 4 . 45 m i l l ion ha o f in landwate r bod ies ( abou t 66%) . Hence 2 m i l l ion ha a res t i l l avai lable to expand f ish farming to i ts fu l lpo ten t ia l , a goa l o f the p resen t governm en t (PRChina MA, 1995) . By the year 2000 , Ch ina expec t sto r each a f r eshwate r f i sh p roduc t ion o f 11 .5 m i l l iontons per year by expand ing the a rea in p roduc t ionand inc reas ing the p roduc t iv i ty o f ponds (PR Ch inaMA , 1995 ; PR Ch ina M AB F, 1995).2 .2 . I ta ly

T he anc ien t Rom ans , s evera l cen tu r ies BC, werefam i l i a r w i th m ethods o f cap t ive b reed ing o f som especies in small ponds : remains of ancient f ishb reed ing ponds can s t i l l be s een a t Po la L ake nearRom e (De M ur tas , 1993) . P l inus , a Rom a n wr i t e r o f

100 BC, p rov ides exam ples o f we l l -m anaged ponds(CE N ASA C, 1987). In fo rm at ion on f ish cap t iveb reed ing in the Vene t ian l agoon can be t r aced backto 1200 BC (De Murtas , 1993) . Clear ly , th is was afo rm o f ex tens ive aquacu l tu re . F inger l ings a r r iv ingf rom the open s ea in sp r ing t im e were t r apped inbas ins ( ' va l l i ' ) o f the l agoon by a r t i f i c ia l dykes .Much a t t en t ion was pa id to avo id ing over s tock ingand over -exp lo i t a t ion o f env i ronm en ta l r esources toavoid a d is rupt ion in the natural t rophic chain (DeMurtas , 1993) .

In the Midd le Ages , aquacu l tu re underwen t g rea tdeve lopm en t , pa r t i cu la r ly in the V ene to r eg ion . T hem ore im por tan t in land f r eshwate r f i sh spec ies weret h e c o m m o n c a r p ( C yp r in u s ca rp io ) , t ench ( T in catinca), p ike ( E x o s l u c i u s ) and t rou t ( S a lmo t ru t ta ,Sa lmo ga irdneri ) . M u l l e t ( M u g i l l i d a e genus) , eel( An g u i l la a n g u i l la ) , sea b ream ( S p a ru s a u ra tu s ) ,a n d M e d i te r r an e a n b a s s ( D i c e n t r a r c h u s l a b ra x ) wereexc lus ive ly r ea red in the ' va l l i ' o f the Vene t ianlagoons (De Murtas , 1993) .

In tens ive aquacu l tu re o f the com m on carp andtrout was f i rs t observed in the second par t of the19 th cen tu ry (CE N ASA C, 1987 ) . In f ac t , by the1960s aquacu l tu re had changed f rom ex tens ive tosem i- in tens ive and f ina l ly to in tens ive p rac t i ces(Melotti et al. , 1994). In 1993, intensive aquacultureaccoun ted fo r near ly a l l o f the to ta l f r eshwate r f i shproduct ion (Melot t i e t a l . , 1994) . Owing to the geo-graphical character is t ics of the I ta l ian peninsula andi ts cul tural t radi t ions , mar ine aquacul ture of molluscs( M yt i lus ga l loprovincia l is , Ostrea e du l is) is the most

T a b l e 1F r e s h w a t e r f i s h p r o d u c t i o n i nQian, 1994)

Ch in a in 1990 ( f rom: FAO, 1993;

A r e a ( h a ) T o t a l p r o d u c t i o n Y i e l dT o n s % o f t o ta l ( k g h a - ~)

P o n d c u l t u re 1 4 1 5 4 3 0 3 3 7 9 5 2 7 7 5 .5 2 3 8 5L akes 615 770 267 340 6 .0 435Rese r vo i r s 1421 590 359 835 8 .0 255Rive rs 331 980 263 749 5 .9 795R i c e - f i s h c u l t u re 7 4 0 8 3 0 1 3 0 8 37 2 . 9 1 8 0Othe r 49 950 66 826 1 .5 1335(cages , t anks e tc . )T o ta l 5025 150 4459 109


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T. Gomiero e t al . / Agriculture, Ecosy stems and Environm ent 62 (1997) 16 9-1 85 17 3

deve loped k ind o f aquacu l tu re in I t a ly (FAO, 1995)(Fig. 2(b)).

I t a ly has 1 50000 h a o f l agoons , 170000 ha o fin land f r eshwate r bas ins and p len ty o f sp r ing wate rpo ten t ia l ly ava i lab le fo r b rack i sh and f r eshwate r p ro -duc t ion . Am ong the E uropean coun t r i es , I t a ly hasp robab ly the m os t f avorab le cond i t ions to deve lopaquacul ture (Melot t i e t a l . , 1994) .

3 . B i o d i v e r s it y u s e i n f r e s h w a t e r a q u a c u l t u r e3 .1 . Me thodo logy and da ta sourc e s

Biod iver s i ty has been def ined by the Conven t ionof B io log ica l D iver s i ty as " the var iab i l i ty am ongliv ing organisms f rom al l the sources , including ter -r es t r i a l , m ar ine and o ther aqua t ic ecosys tem s andeco log ica l com plexes o f wh ich they a re par t ; th i sinc ludes d iver s i ty w i th in spec ies , be tween spec iesand o f ecosy s tem s" ( Johnson , 1993). T h i s de f in i t ionc lea r ly ind ica tes tha t we a re dea l ing w i th a r a thercom plex concep t , d i f f i cu l t to expres s w i th num er ica lindicators . In fact , the par t icular genet ic composi t ionof a s ingle species , the occurrence and relat ive abun-dance o f spec ies in eco log ica l com m uni t i es , and thed i s t r ibu t ion o f ecosys tem types in the b iospherechange over d i f f e ren t t im e- sca les in r esponse to na t -u ra l and hum an- induced changes .

In th i s paper , we s im ply 'm easu re ' b iod iver s i tyuse in aquacu l tu re by the num ber o f spec ies cu l tu red

toge ther in an ind iv idua l p roces s o f f i sh p roduc t ion .T he cho ice o f th i s ind ica to r i s ce r ta in ly a rguab les ince any p roxy fo r the concep t ' b iod iver s i ty use ' i snecessar i ly arbi t rary . On the other hand, as eachspecies rel ies on i ts own ecological n iche, the num-ber o f spec ies cu l t iva ted toge ther in a d e f ined wate rbody p rov ides an ind ica t ion o f the com plex i ty o f thesys tem o f na tu ra l con t ro ls invo lved in the p roces s. Ala rger num ber o f p roduced spec ies in the s am e wate rbody i s ind ica t ive o f the ab i l i ty o f the m anagedecosys tem to conver t in a coord ina ted way a l a rgerset of mat ter inputs in to f ish b iomass , while d ispos-ing o f was tes and by -p roduc t s .

Da ta on Ch inese and I t a l i an f r eshwate r f i sh cu l -tu re were ob ta ined f rom the l i t e r a tu re and th roughper sona l com m unica t ion w i th s c ien t i f i c exper t s andproducers . Data include the species reared, naturalf eed ing hab i ts , and m etho d o f p roduc t ion .3.2 . Chinese polycul tural sys tem

Fish po lycu l tu re l i t e r a l ly m eans r ea r ing s evera lspec ies o f f i sh in the s am e wate r body . As d i f f e ren tspec ies have d i f f e ren t eco log ica l n iches ( they f eedon d i f f e ren t resources ) , a ba lanced p o lycu l tu ra l sys -tem has the potent ial to reach ful l resource exploi ta-t ion of the water body (Shan, 1987; Zhong, 1992) .

T he f i sh pond i s an a r t i f i c ia l ecosys tem whereex te rna l inpu t s o f f eed and f e r t i l i ze r a r e im por tan t ,bu t where in te rna l charac te r i s t i c s o f the m anagedeco sys tem s t i ll p lay a fun dam ental ro le in the regula-

T a b l e 2C h i n e s e p r o d u c t i o n f r o m a q u a c u l t u r e f o r t h e m a j o r f i s h s p e c i e s a n d t h e i r f e e d i n g h a b i t ( f r o m F A O , 1 9 9 5 , u p d a t e o f 1 9 9 3 d a t a )S p e c i e s E n g l i s h n a m e 1 9 9 3 ( t o n s) % F e e d i n g h a b i tHypophtha lmich thys m ol i t r ixs S i l v e r c a r p 1 8 0 6 5 9 2 2 7 . 9 H e r b i v o r o u sCtenopharyngodon idella G r a s s c a r p 1 4 6 4 9 4 5 2 2 . 7 H e r b i v o r o u sAris t i ch thys nob i l l s B i g h e a d c a r p 9 0 1 9 4 2 1 4 . 0 Z o o p l a n k t i v o r o u sCyprinus carpio C o m m o n c a r p 8 91 6 2 4 1 3 .8 B e n t h i v o r o u sTilapia ni lot icus N i l e t i l a p ia 5 3 2 5 0 0 8 . 2 H e r b i v o r o u sCarasius carassius C r u c i a n c a r p 2 9 1 5 2 9 4 . 6 B e n t h i v o r o u sParabram is pek inens i s W h i t e a m u r b r e a m 2 1 8 9 2 1 3 . 8 H e r b i v o r o u sCirrhina moli torel la M u d c a r p 1 0 0 0 0 0 1 .7 B e n t h i v o r o u sM y l o p h a r i n go d o n p i c e u s B l a c k c a r p 6 5 6 3 8 1 .2 B e n t h i v o r o u sOth e r spec i e s 128 257 2 .1T o t a l 5 8 6 9 4 4 8 1 0 0 ,0


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17 4 T. Gomiero e t a l . /Agr icu l tu re , Ecosys tems and Env ironment 62 (1997) 16 9-18 5

t i on o f ma t t e r a nd e ne rgy f l ows (L i , 1987) . In t heCh i ne se po l yc u l t u ra l sy s t e m, a s ma ny a s e i gh t o re ve n n i ne f i sh spe c i e s c a n be r e a re d i n t he s a mepond i n a ba l a nc e d c ombi na t i on o f s i z e a nd numbe r .F i sh f a rmi ng po l yc u l t u re i s pe r fo rme d a t e ve ry r e a r -ing s tage in China (Shan, 1987; Zhong, 1992) . Gen-e ra l l y , be t we e n one a nd t h re e f i sh spe c i e s a re r e a re da s p r i nc i pa l spe c i e s , the o t h e r spe c i e s a re c ons i de re da s s e c onda ry (F AO , 1980a ; S ha n , 1987 ; Zhon g ,1992) . The c ho i c e o f p r i nc i pa l a nd s e c ond a ry spe c i e sde pe nds on t he f i sh e nv i ronme n t a l ne e ds , f e e d a ndma nure a va i l a b i l i t y , f a rmi ng t e c hn i que s , pond c ond i -t ions , and marke t demand (Lin , 1982; Shan, 1987;Zhong , 1992) .

The more i mpor t a n t spe c i e s c u l t i va t e d i n Ch i naa re s i l ve r c a rp , g ra s s c a rp , b i ghe a d c a rp , a nd c om -m o n c a r p . T h e s e f o u r s p e c ie s a c c o u n t e d f o r 8 6 % a n d80% of t he t o t a l p roduc t i on i n 1990 a nd 1993 ,re spe c t i ve l y (F AO , 1995) (Ta b l e 2 ) . The w i de sp re a da dop t i on o f t he se spe c i e s i n ponds a nd re se rvo i r st h roughou t Ch i na i s e xp l a i ne d by t he fo l l owi ng fa c -tors (FA O , 1980a , 1992; Lin , 1982; Shan, 1987;Zh ong , 1992; Li and M athias , 1994) . F a vora b l e f e e d i ng ha b it s a nd e c o l og i c a l c ha ra c t e r -

i s t ic s . S i lve r ca rp and bighead ca rp a re f i l t e r-f e e de r s ( t he fo rme r on phy t op l a nk t on , t he l a t t e ron z oop l a nk t on ) , g ra s s c a rp f e e d on ma c rophy t e sa n d c o m m o n c a r p f e e d o n o r g a n i c m a t er i al o n t h ebo t t om. He nc e , t he se spe c i e s f e e d l ow i n t he foodc ha i n a nd re l y on na t u ra l p roc e s se s t a k i ng p l a c ewi t h i n t he wa t e r bod y fo r t he i r fe e d . The se spe c i e sc a n t he re fo re be p roduc e d t h rough fe r t i l i z a t i onprograms tha t u t i l i ze loca l resources wi th l i t t l e orno supp l e me n t a ry f e e d . The y ha ve a sho r t g rowt hpe r i od a nd a re e a sy t o f e e d a nd ha rve s t .

S i mp l e t e c hno l og i e s fo r ar t if i c ia l b ree d i ng . Mi n i m a l r e qu i re me n t s o f c a p it a l inpu t a nd t e c h -

no l og i e s fo r bo t h f ry a nd f i nge r l i ng re a r i ng , a ndfo r g rowi ng t he m t o ma rke t a b l e f i sh .P roduc t i on t e c hn i que s i n po l yc u l t u re t e nd t o c re -

a t e a na t u ra l - l i ke pond e nv i ronme n t t ha t i m i t a t e s a smuc h a s pos s i b l e t he c ompl e x t roph i c s t ruc t u re wi t hl i nks be t we e n e nv i ronme n t a l r e sou rc e s , m i c roo rga n -i sms , p l a n t s , he rb i vo re s , c onsume rs , a nd t op p re da -t o r s . Th i s p roduc t i on sys t e m fo l l ows t he so -c a l l e dpa ra d i gm o f ' e c o l og i c a l a g r i c u l t u re ' wh i c h ha s be e nde ve l ope d i n r e c e n t ye a r s i n Ch i na . Ec o l og i c a l a g r i -c u l t u r e " e m p h a s i z e s t h e r e l a t i o n s h i p b e t w e e n c o m -

pone n t s wi t h i n t he sys t e m a nd t he r e l a t i onsh i p be -t we e n a g roe c osys t e ms a nd t he i r na t u ra l a nd soc i a le nv i ron m e n t s " (L uo a nd Ha n , 1990 , p . 305 ) .3 .3 . I t a l ian in t e ns i v e mo noc u l tu ra l s y s t e m

In t e ns i ve mono c u l t u ra l sy s t e ms a c c oun t fo r ne a r l ya l l o f t he p roduc t i on o f f r e shwa t e r f i sh i n I t a l y(Ghi t t ino , 1983; Giordani and Melot t i , 1984; DeM urtas, 1993; M elott i e t a l ., 1994). Art ific ial tank sare the major f reshwate r bodies in use . In a r t i f ic ia lt a nks t he wa t e r f l ux i s ma i n t a i ne d c ons t a n t by e l e c -t r ic pumps , a nd ox yge n i s c on t i nuous l y i n su f f l a t ed i nt he wa t e r (Gh i t t i no , 1983 ; Gi o rda n i a nd Me l o t t i ,1984). Of t e n , me d i um a nd l a rge f i sh f a rms h a ve t he i row n ha t c he ry (Me l o t t i e t al ., 1994) .

I t a l i a n i n t e ns i ve monoc u l t u ra l sy s t e ms re l y onc a rn i vo rous f i sh spe c i e s fo r 85% o f t he i r p roduc t i on(Ta b l e 3 ) . Be s i de s b i ophys i c a l e xp l a na t i ons , t h i sc ho i c e i s a l so d r i ve n by t he s t rong p re fe re nc e o fI t a l i a n c onsume rs fo r c a rn i vo rous r a t he r t ha n he rb i v -orous spec ies . In 1993, a s ingle spec ies ( t rout ) ac -c o u n t e d f o r 7 1 % o f t h e t o t al p r o d u c t i o n o f f r e s h w a -t e r f i sh , wh i l e t he t op t wo spe c i e s ( t rou t a nd e e l )t oge t he r a c c oun t e d fo r 77% o f t he t o t a l (Me l o t t i e ta l. , 1994 ; F AO , 1995). T rou t a nd e e l a re c a rn i vo rousf i sh tha t a re fed wi th indus t r ia l pe l le t s wi th a h igh(a bou t 40% ) a n i ma l p ro t e i n c on t e n t (Gh i t t i no , 1983 ;Gio rdan i and Melot t i , 1984; W atanab e , 1986; Cho e ta l . , 1994) . Indus t r ia l pe l le t s a re made up mainly of

T a b l e 3I t al i a n p r o d u c t i o n f r o m a q u a c u l t u r e f o r t h e m a j o rt h e i r f e e d i n g h a b i t (f r o m F A O , 1 9 95 , u p d a t e d o f

f i s h s p e c i e s a n d1993 data)

S p e c i e s E n g l i s h n a m e T o n s % F e e d i n g h a b i tOncothynchus T rou t 35 500 70 .6 P isc ivo rousm y k u sAngui l la angu i l la E e l 3 0 0 0 6 . 0 P i s c i v o r o u sMugi l l idae ( g e n u s ) M u l l e t 3 0 0 0 6 . 0 H e r b i v o r o u sDicen trarchus M e d i t e r r a n e a n 2 0 0 0 4 . 0 P i s c i v o r o u slabrax b a s sl c ta lunus melas Catf i sh 1750 3 .5 P isc ivo ro usSparus aura tus S e a b r e a m 1 3 00 2 . 6 B e n t h i v o r o u sC~prinus carpio C o m m o n c a r p 3 5 0 0 . 7 B e n t h i v o r o u sA c i p e n s e r i d a e S t u r g e o n 3 1 0 0 . 6 B e n t h i v o r o u sO t h e r s p e c i e s 3 1 0 0 6 . 0T o ta l 5031 0 100


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T. G omiero et a l ./ Agriculture, Ecosystems and Environment 62 (1997) 169-185 175f i sh me a l ob t a i ne d f rom ma r i ne c a t c h (W a t a na be ,1986) . On a ve ra ge , 0 .5 kg o f d ry ma r i ne f i sh me a lfe e d i s c onve r t e d in t o 1 kg o f we t f r e sh f ish b i oma ss( t he ou t pu t o f a qua c u l t u re ) (L . Co l ombo , pe r sona lc ommuni c a t i on , 1996) . Cons i de r i ng t ha t 0 .5 kg o fd ry f i sh me a l u se d a s f e e d i n f r e shwa t e r a qua c u l t u rere qu i re s 5 kg o f f r e sh ma r i ne c a t c h , 1 kg o f we t f i shwe i gh t p roduc e d i n t h i s wa y re qu i re s 5 kg o f f r e shm a r i n e c a t ch ( L . C o l o m b o , p e r s o n a l c o m m u n i c a t io n ,1996) . Indus t r ia l pe l le t s a re used as feed for a l lspe c i e s p roduc e d unde r i n t e ns i ve a nd s e mi - i n t e ns i vec u l t u re . Ma nure a nd c he mi c a l f e r t i l i z e r s a re u se don l y i n some se mi - i n t e ns i ve a nd e x t e ns i ve p roduc -t i on sys t e ms , wh i l e i n some e x t e ns i ve wa t e r bod i e s(e .g . l a goons ) no i npu t s a re u se d a t a ll (Gi o rda n i a ndMe l o t t i , 1984 ; A . P e ro l o , pe r sona l c omm uni c a t i on ,1996).

Te c hno l og i c a l p rog re s s i n i n t e ns i ve a qua c u l t u re ,suc h a s t he a dop t i on o f i mprove d wa t e r r e c i r c u l a t i onsys t e ms , c ou l d i mprove c onve rs i on fa c t o r s i f t hei nnova t i ons a re c ompa t i b l e wi t h t he b i ophys i c a l a ndsoc i oe c onomi c c ons t ra i n t s a f fe c t i ng t he p roduc t i ono f t rou t a nd e e l .3 . 4. P a t t e r n s o f tr o p h i c n i c h e e x p l o i ta t i o n

The fe e d i ng ha b i t s o f spe c i e s r e a re d i n Ch i na a ndI t a l y a re c ompa re d i n F i g . 3 (a ) a nd (b ) (da t a f romTa b l e s 2 a nd 3 ) . As no t e d e a r l i e r , Ch i ne se p roduc -t i on re l i e s on spe c i e s wh i c h fe e d l ow i n t he foodc ha i n : p l a nk t i vo rous , he rb i vo rous , a nd bo t t om o r -ganic de t r i tus feed ers (Li , 1987; Shan, 1987; Zho ng,1992; Li and M athias , 1994). In 1993, phy toplan k-t i vo rous a nd ma c rophy t e -e a t i ng spe c i e s a c c oun t e dfo r a bou t 63% o f t o t a l Ch i ne se p roduc t i on , z oop l a nk-t i vo rous spe c i e s fo r a bou t 14% , a nd be n t h i vo rousspe c i e s ( f e e d i ng on o rga n i c de t r i t u s o r bo t t om fa una )fo r a bou t 21% (F A O, 1995) (F i g . 3 (a) ) .

S i n c e o n l y a b o u t 1 0 - 2 0 % o f th e e n e r g y f r o m at roph i c l e ve l c a n be c onve r t e d i n t o body ma ss o fo rga n i sms be l ong i ng t o t he h i ghe r t roph i c l e ve l(Od um , 1983), t he p r i nc i pa l a i m o f f ish c u l t u re inCh i na i s to e n ha nc e t he u t i l iz a t i on o f b i o l og i c a lre sou rc e s by ke e p i ng t he food c ha i n sho r t . In t h i swa y , i t is pos s i b l e t o a c h i e ve a h i gh e f f i c i e nc y inu t i li z i ng b i o l og i c a l c onve rs i ons w i t h i n t he e c osys t e m(Li , 1987, 1995; Zh ong , 1992) .

I ta l ian produc t ion , on the o ther hand, re l ies a l -

( a ) piscivorousbenti . . . . . . . .

mzooplanktivorousphytopl anktivorous ~ ~

0 2 0 4 0 6 0

percentage of total productionI

8 0

( b ) piscivorousd~ ben t ivorous

"~ zooplanktivorous

phytoplanktivorous' 2 ' 0 ' 4 1 0 ' 6 ' 0 ' 8 ~ 0 ' 1 O 0percentage of total production

Fig. 3. (a) Trophic pyramid of cultured freshwater fishes in PRChina. (b). T roph ic pyram id of cultured freshwater fishes in Italy.

mos t e xc l us i ve l y on c a rn i vo rous spe c i e s . F i she s f e e don i ndus t r i a l pe l l e t s , t he p ro t e i n c on t e n t o f wh i c hc ome s ma i n l y f rom ma r i ne f i sh me a l (F i g . 3 (b ) ) .W i t h t h i s so l u t i on t he t roph i c c ha i n be c ome s a s t e pl onge r a nd t he e ne rgy e f f i c i e n c y o f t he t roph i c c ha i ni s re d u c e d b y 8 0 - 9 0 % . N o t e t h a t p ro t e i n -r i c h f e e d i sa l so g i ve n t o t hose spe c i e s wh i c h do no t ne e d i t ,suc h a s c om mo n c a rp (W a t a na be , 1986) , t o spe e d upthe i r growth. In fac t , under na tura l condi t ions th i sspe c i e s f e e ds on bo t t om i nve r t e b ra t e s a nd o rga n i cdetri tus.

4 . Tech n ica l ch aracter i s ti c s o f aq u acu l tu re4 .1 . F r e s h w a t e r f i s h b i o m a s s p r o d u c t i o n

In 1990 , t o t a l f r e shwa t e r f ish p rodu c t i on in C h i nar e a c h e d 4 4 5 9 1 14 t o n s o n a s u r f a ce o f 4 5 7 5 5 5 0 h a(FAO, 1993; Qian, 1994) , resul t ing in a gross aver-a g e p r o d u c t i o n o f 9 7 5 k g h a - ~ y e a r - 1. T h e a v e r a g ep roduc t i v i t y o f Ch i ne se po l yc u l t u ra l pond sys t e ms i sh i ghe r , a nd ha s be e n e s t i ma t e d a t 24 00 kg ha -~


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176 T . Gom iero e t a l . / Agr icu l tu re , E cosys tems an d Env iron men t 62 (1997 ) 169 -185

ye a r - i (F AO , 1993 ; Qi a n , 1994) (Ta b l e 4 ) . A re c e n ts t udy on i n t e g ra t e d f i sh f a rmi ng ponds fo r s e ve nprov i nc e s i n e a s t Ch i na re po r t s t ha t i t i s pos s i b l e t oa c h i e v e h i g h e r y i el d s ( u p t o 6 1 0 0 k g h a - 1 ) b y a ni n t e ns i ve r e c yc l i ng o f f a rm by -p roduc t s a nd someuse of feed (Chen e t a l . , 1995) .

In 1993 , I t a l i a n t rou t f a rmi ng ha d a n a ve ra gep r o d u c t i v i ty o f 1 0 0 0 0 0 k g h a - 1 a n d e e l f a rm i n g h a da n a ve ra ge p rodu c t i v i t y o f 65 000 kg ha -1 . O t he rspe c i e s , suc h a s s e a b re a m, Me d i t e r ra ne a n ba s s , a ndm u l l et , h a d a n a v e r a g e p r o d u c t i v i ty o f 2 0 0 0 0 k gha -~ (Me l o t t i e t a l. , 1994 ; A . P e ro l o , pe r sona l c om-mun i c a t i on , 1996) . The we i gh t e d a ve ra ge o f t hep roduc t i v i t y o f t he ma i n c u l t i va t e d spe c i e s i s a bou t8 0 0 0 0 k g h a - l ( T a b l e 4 ) . A s t h e It al ia n m o n o c u l -t u ra l sy s t e m i s ba se d on a r t i f i c i a l wa t e r t h roughpu t ,p roduc t i v i t y i n I t a l y ma y be be t t e r e xp re s se d i nt e rms o f f i sh we i gh t pe r c ub i c me t e r o f wa t e r r a t he rt ha n pe r un i t o f su r fa c e . I f t he a bove va l ue s o fp rod uc t i v i t y ( in kg ha - J ) a re c onv e r t e d t o k i l og ra msof f i sh pe r c ub i c me t e r o f r e a r i ng spa c e , wa t e re xc ha nge be c ome s a p i vo t a l pa ra me t e r . W i t h a t yp i -c a l r a te o f w a t e r e x c h a n g e o f 4 - 6 1 s - ~ p e r t on o ff i sh s tocked (Melot t i e t a l . , 1994) , produc t iv i ty i sa b o u t 3 0 - 4 0 k g m - 3 y e a r - ~ ( T a b le 4 ).

4 .2 . Freshwa ter f i sh b iomass p roduc t ion pe r hour o flabor

To a s se s s t he l a bo r p roduc t i v i t y i n t he a qua c u l -t u ra l s e c t o r , we d i v i de d t he a gg re ga t e p roduc t i on o ft he s e c t o r by t he a gg re ga t e l a bo r supp l y ( a s sumi nga n a ve ra ge o f 1800 l a bo r hours pe r worke r pe r ye a r ) .As t h i s me t hod p rov i de s a r a t he r rough a pp rox i ma -t ion , we checked the resul t s aga ins t va lues ava i lablef rom pub l i she d c a se s t ud i e s a nd a c t ua l p roduc t i ons i t e s whe re pos s i b l e , a nd submi t t e d e s t i ma t e s t o e x -pe r t s i n bo t h c oun t r i e s . F o r Ch i na , we re l i e d he a v i l yon da t a f rom Qi a n (1994) t ha t r e fe r t o 1990 e s t i -ma t e s o f huma n p ow e r in i n l a nd a qua cu l t u re. Th ee s t i ma t e d l a bo r p rodu c t i v i t y is r e po r t e d i n Ta b l e 4 .

Ch i ne se pond c u l t u re r e qu i re s t wo fu l l - t i me work -e r s pe r he c t a re o f pond su r fa c e (Qi a n , 1994). Cons i d -e r in g a n a v e r a g e p o n d p r o d u c t i v i ty o f 2 4 0 0 k g h a -a n d a n a v e r a g e w o r k l o a d o f 1 8 0 0 h o u r s p e r w o r k e rpe r ye a r , we ob t a i n a l a bo r p roduc t i v i t y o f a bou t 0 .7kg h -1 .

In I t a l i a n i n t e ns i ve f i sh f a rmi ng , wh i c h a c c oun t sfo r a l mos t t he e n t i r e f r e shwa t e r f i sh p roduc t i on ,y i e l d s p e r w o r k e r a r e i n t h e r a n g e 4 0 0 0 0 - 1 4 0 0 0 0k g y e a r - ~ d e p e n d i n g o n t h e t y p e o f p r o d u c t i o n ( A .

T a b l e 4T e c h n i c a l p e r f o r m a n c e o f a q u a c u l t u r e in P R C h i n a a n d I t a l y

P R C h i n a I t a l yT h r o u g h p u t d e n s i t yL a b o r p r o d u c t iv i t y ( k g h - J ) aP r o d u c t iv i t y p e r u n it a r e a o f w a t e r b o d y ( k g h a - I y e a r - ~) ~P r o d u c t iv i t y p e r u n it v o l u m e o f w a t e r b o d y ( k g m - 3 y e a r - ~) b

D e p e n d e n c e o n e x t e r n al i n p u t s% o f t o ta l f e e d e n e r g y i m p o r t e d aN i t ro g e n i n p u t / o u t p u t ( i m p o r t e d / e x p o r t e d ) aF o s s i l e n e rg y i n p u t / f i s h e n e r g y o u t p u t r a t io ( k c a l k c a l - i )

E n v i r o n m e n t a l s t r e ssF r e s h w a t e r c o n s u m p t i o n (I y e a r - i k g - i o u t p u t) ~N i t r o g e n i n w a t e r w a s te ( k g y e a r - t h a - ~ o f w a t e r b o d y ) cB i o d i v e r s i t y u s e ( n o . o f c u l t u r e d s p e c i e s i n s y s t e m ) a

= 1 2 0 - 8 0= 2 4 0 0 = 8 0 0 0 00 . 1 - 0 . 2 3 0 - 4 0

35 1002 . 5 / 1 3 0 / 1< O . 1 2 0 - 4 5

7 0 0 0 = 2 0 0 0 0 0N e g l i g i b l e > 3 0 0 0 04 - 9 ( u p t o 1 4 ) 1

a E s t i m a t e d ( s e e t e x t f o r s o u r c e s a n d a s s u m p t i o n s ) .b A v e r a g e w a t e r d e p t h 1 . 5 - 2 . 0 m , t u r n o v e r o f w a t e r i n It a ly 5 k g s - i t o n - 1 f i sh .c D r e s s e d w e i g h t o f f i s h 5 5 % , p r o t e in c o n t e n t o f d r e s s e d w e i g h t 1 5 % , n i tr o g e n e q u a l s 1 6 % o f p r o t ei n ; n i t ro g e n i n p u t / o u t p u t r a ti o a n dp r o d u c t i v i t y p e r h e c t a r e i n t h i s t a b l e .


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T. Gomiero et al. / Agriculture, Ecosystems and Environment 62 (1997) 169-185 177

Pero lo , pe r sona l com m unica t ion , 1996) . W i th a w orkload o f 1800 hour s pe r year pe r worker , the l aborp roduc t iv i ty i s in the r ange 20 -8 0 kg h -~ (T ab le 4) .

As discussed la ter , the d if ference in labor produc-t iv i ty be tween these two sys tem s i s due to a l a rged i f f e rence in the i r u se o f eco log ica l s e rv ices , em bod-ied in inpu t s and r equ i r ed fo r r ecyc l ing was tes , anduse o f t echno log ica l inpu t s .4.3 . Ni trogen conversion index

reared f ish species as an indicator of b iodivers i tybecom es ev iden t . In r ea l i ty , the d i f f e rence be tweenthe b iod iver s i ty p resen t in Ch inese po lycu l tu ra l pondsand I t a l i an f r eshwate r t anks i s m uch m ore p ro -nounced than the num er ica l ind ica t ion r epor ted inT ab le 4 . Ma ny spec ies be long ing to lower t axonom icgroups a re beh ind the p roduc t ion o f f i sh in thepo lycu l tu ra l pond sys tem . T hese spec ies a re absen tin the a r t i f i c ia l env i ronm en t typ ica l o f ' h igh t ech 'f r eshwate r aquacu l tu re .

T he n i t rogen conver s ion index i s he re def ined asthe n i t rogen inpu t /ou tpu t r a t io , where the inpu tequa l s the am oun t o f n i t rogen in t roduced in to thesys tem , inc lud ing f e r t i li ze r and f eed ( in kg ) , and theou tpu t equa l s the am oun t o f n i t rogen in the f i shb iom ass p roduced (kg ) .

Guo and Bradshaw (1993) p rov ide a n i t rogenconver s ion index o f 2 . 2 fo r a Ch inese in teg ra ted f i shfa rm , and a va lue o f 3 .1 fo r ponds in J angsu P rov incein eas t Ch ina . T hese as ses sm en ts cons ider as inpu ton ly n i t rogen f rom ou ts ide the f a rm ing sys tem anddo no t inc lude n i t rogen f rom recyc led o rgan ic m ate -r i a l w i th in the f i sh f a rm ing sys tem . G iven theseas ses sm en ts , we adop ted an es t im ate o f the n i t rogenindex of 2 .5 (Table 4) .

Cho e t a l . ( 1994) p rov ide a n i t rogen conver s ionindex o f 30 fo r in tens ive t rou t m onocu l tu re in I t a ly(Table 4) . Note that whereas the n i t rogen input inCh inese ponds i s in the fo rm o f bo th f e r t i l i ze r andfeed, here al l n i t rogen input is in the form of indus-trial pellets .

T h e n i t r o g e n i n p u t / o u t p u t r a t i o s f o r C h i n a a n dI ta ly d i f f e r m arked ly , and consequen t ly the eco log i -ca l im p l ica t ions o f the n i t rogen f low a re d i f f e ren t fo rthese two coun t r ies . In Ch inese po lycu l tu ra l sys tem s ,the n i t rogen app l ied in exces s o f the am oun t r equ i r edby the cul tured f ish is not los t , nor does i t representpol lu t ion. I t remains ins ide the closed rear ing sys temand con t r ibu tes to conserv ing the aqua t ic ecosys temstructure. On the other hand, in indus tr ia l f ish farm-ing in ar t i f ic ial water bodies , surplus n i t rogen in thefo rm o f unea ten f eed and f i sh excre ta is lo s t w i th thewate r was te to the ex te rn a l env i ronm en t , thus con-t r ibu t ing to eu t roph ica t ion and degrada t ion o f lo t i cwater bodies (Sumari , 1986; Cho et a l . , 1994; Ober-do ff and Porcher , 1994) .

Here the s im pl i f i ca t ion o f u s ing the num ber o f

4.4 . Ef f ic iency in using the natural t rophic chainE ff ic iency in us ing the na tu ra l t roph ic cha in can

be as ses sed by the percen tage o f f eed energy gener -a ted w i th in the sys tem i tself .

A s tudy o f Guo and Bradshaw (1993) on energyand e lem en t f lows fo r som e Ch inese f i sh pond cu l -tu res shows tha t 65% of the food energy p roducedby pond s in the fo rm o f f i sh b iom ass i s de r ived f romnatu ra l f eed inpu t s genera ted by na tu ra l p roces seswi th in the pond (T ab le 4 ) .

In in tens ive sys tems of product ion in I ta ly , theam oun t o f f eed energy genera ted w i th in the sys temitself is negl ig ible (Ghit t ino, 1983; Giorda ni andMe lot t i , 198 4; De Mu rtas , 1993; Melot t i e t a l . , 1994)(Table 4) .4 .5 . D ep en d en ce o n fo ss i l en erg y

Depend ence on fos s i l energy can be de f ined by anenergy inpu t /ou tpu t r a t io where the inpu t equa l s theam o un t o f fos s i l energy ( in kca l ) spen t in the var iousinpu ts consum ed in the p roduc t ion p roces s and theou tpu t equa l s the b iom ass energy p roduced in thefo rm o f f i sh (kca l ) .

Fo r Ch ina , Guo and Bradshaw (1993) r epor t tha tthe am oun t o f fos s i l energy em bod ied in im por tedinpu ts i s abou t 3% of the food energy ou tpu t . O therenergy inputs required to run the ponds (e .g . indus-t r ia l ar ti facts , t ranspor tat ion) are in the sam e orde r ofm agn i tude . Hence the inpu t /ou tpu t r a t io w i l l besmaller than 0 .1 (Table 4) .

In I t a ly , the inpu t s invo lv ing con sum pt ion o f fos -s il energy inc lude those l i s t ed be low . E lec t r i c ity fo r pum p ing wate r and the func t ion ing

of the p lan t : 1 . 5 -4 kW h kg-~ o f p roduced t rou t(es t imated by the f i rs t author on the bas is of h is


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178 T. Gom iero et aL /Agriculture, Ecosystem s and Environm ent 62 (1997) 169-185s t udy o f s e ve ra l I t a li a n p roduc t i on s i t e s ) o r 400 0-1 0 0 0 0 k c a l o f f o s s i l e n e r g y ( 1 k W h = 8 6 0 k c a l ,a n d 3 k c a l o f f o s s i l e n e r g y a r e c o n s u m e d t op roduc e 1 kc a l o f e l e c t r i c i t y ) .

Ene rgy fo r ma k i ng a va i l a b l e pe l l e t s , i nc l ud i ngma r i ne c a t c h , p roc e s s i ng , pa c ka g i ng , a nd t r a ns -po r t a t i on . Us i ng t he a s sumpt i ons d i s c us se d a bove(1 kg o f d ry pe l le t s is ne e de d fo r 2 kg o f w e t t rou tp r o d u c e d ; 5 k g o f f r e sh c a t c h n e e d e d p e r k g o fd r y p e l l e t ) a n d a f o s s i l e n e r g y c o n s u m p t i o n o f5 0 0 0 - 1 0 0 0 0 k c al k g - ~ o f m a r in e f r e s h c a tc h(P i me n t e l a nd P i me n t e l , 1979 , pp . 10 9 -11 1) , w eo b t a i n a n e n e r g y r e q u i r e m e n t o f 1 2 5 0 0 - 2 5 0 0 0k c a l k g - ~ o f t r o u t p r o d u c e d .

Th e fo s s il e ne rg y spe n t i n the bu i l d i ng a nd ma i n -t e n a n c e o f t h e p l a n t a n d e q u i p m e n t ( d i s c o u n t e dove r i t s l i f e spa n ) i s e s t i ma t e d a t 25% o f t hee ne rgy spe n t on runn i ng t he p l a n t (P i me n t e l a ndP i me n t e l , 1979) , t hus a r r iv i ng a t a r a nge o f 1 00 0-2500 kc a l kg -~ o f t rou t p roduc e d . W e s l i gh t l yi nc re a se d t h i s es t i ma t e t o 150 0-3 000 kc a l kg -~t o i nc l ude fo s s i l e ne rgy e mbod i e d i n t he c he mi -c a l s a nd me d i c i na l d rugs u se d i n t he p l a n t .S ummi ng a l l t he se i npu t s , we ob t a i n a rough

e s t im a t e o f 1 7 0 0 0 - 4 0 0 0 0 k c a l o f f o s s il e n e r g y i n p u tp e r k g o f t r o u t p r o d u c e d . H e n c e , t h e i n p u t / o u t p u te n e r g y r a ti o w i ll be in th e r a n ge 2 0 / l - 4 5 / 1 ( T a b le4 ) .4 .6 . D e m a n d o n t h e e n v i r o n m e n t : F r e s h w a t e r r e-q u i r e m e n t

F re shwa t e r c onsumpt i on i n t he r e a r i ng p roc e s s i sa n i n d i c a ti o n o f t h e d e m a n d o n t h e e n v i r o n m e n tg e n e r a t e d b y t h e p r o d u c t i o n s y s t em .

In C h i na , e x t e rna l f r e shwa t e r i s ne e de d t o o f f - s e te va pora t i on i n t he f i sh pond a nd t o r e f i l l t he ponda f t e r f i sh ha rve s t . W i t h a n a ve ra ge pond de p t h o f1 .5 -2 m (S ha n , 1987 ; Zhong , 1992) a nd a n a ve ra gey e a r l y p r o d u c t i v i ty o f 2 4 0 0 k g h a - 1 , w e f i n d t h a t0 . 1 2 - 0 . 1 7 k g o f f i s h a re s t o c k e d p e r s q u ar e m e t r e o fsu r fa c e . Th i s r e su l t s i n a wa t e r r e qu i re me n t o f a bou t6 - 8 m 3 o r 6 0 0 0 - 8 0 0 0 1 k g - 1 o f f is h p r o d u ce d p e ry e a r ( T a b l e 4 ) .In I t a l i a n i n t e ns i ve f i sh f a rmi ng (e . g . t rou t a nde e l ) , a n a ve ra ge o f 5 1 f r e shw a t e r pe r s e c ond pe r t onof f i sh s tocke d a re requ i red (M elot t i e t a l ., 1994) . A st he a ve ra ge s t oc k i ng t i me t o ob t a i n ma rke t a b l e f i sh

i s 15 mon t hs , w a t e r c onsu mp t i on is a bou t 200 000 0001 f r e shwa t e r pe r t on o f f i sh ou t pu t , o r 20 0 000 1 kgo f f i sh (Ta b l e 4 ) .4 . 7. E n v i r o n m e n t a l s t r e ss : R e l e a s e o f w a s t e p r o d u c t s

W a s t e p roduc t s f rom i n t e ns i ve f i sh f a rmi ng i n -c l ude r e s i dua l f e e d , e xc re t a (e . g . a mmo ni a ) , c he m i c a lsubs t a nc e s , pa t hoge n i c ba c t e r i a , a nd pa ra s i t e s(S uma r i , 1986 ; Ob e rdo r f a nd P o rc he r , 1994). Th ea m o u n t o f w a s t e p r o d u c e d v a r i e s g r e a t l y d e p e n d i n gon fe e d i ng a c t i v i t i e s , s e a son , ma na ge me n t , e t c . Ac -c u ra c y i n mon i t o r i ng e f f l ue n t s wo u l d i mp l y a c ons id -e ra b l e i nc re a se i n ope ra t i ng c os t s (C ho e t a l . , 1994)a nd c on se que n t l y l i tt l e has be e n done t o da t e t oe s t i ma t e t he l oa d o f wa s t e p roduc t s r e l e a se d i n t ona t u ra l wa t e r bod i e s (Ob e rdo r f a nd P o rc he r , 1994).

In a ny c a se , we c a n s a fe l y s t a t e tha t t he r e l e a se o fwa s t e p roduc t s i n t o t he e nv i ronme n t i s muc h l owe ri n t he C h i ne se po l yc u l t u ra l sy s t e m, whe re t he ve ryra t i ona l e o f t he ma na ge me n t t e nds t o p re ve n t t h i sk i nd o f p rob l e m , t ha n i n t he I t a l ia n sys t e m. S t oc k i ngc o m p l e m e n t a r y s p e c ie s t o g e t h e r p r ev e n t s w a t e r p o l -l u t ion f rom fe c a l wa s t e . F o r e xa m pl e , W uc h a n b re a mfe e d on g ra s s c a rp e xc re t a (S ha n , 1987 ; Zhong ,1992) . Also , the s tocking of f i sh spec ies in Chin eseponds a t a muc h l owe r de ns i t y t ha n t ha t a dop t e d i ni n t e ns i ve monoc u l t u ra l sy s t e ms i n I t a l y ma ke s t heou t b re a k o f e p i de mi c d i s e a se s l e s s p roba b l e i n C h i -ne se sys t e ms , t hus a l l owi ng t he C h i ne se t o u se on l yfe w d rugs a nd o t he r c he mi c a l s (S ha n , 1987 ; Zhong ,1992).

5 . F r e s h w a t e r a q u a c u l t u r e i n it s so c i o e c o n o m i cc o n t e x t5 .1 . P e r f o r m a n c e o f f r e s h w a t e r a q u a c u l t u r e i n t h en a t i o n a l e c o n o m y

T h e g r o s s d o m e s t i c p r o d u c t ( G D P ) p e r c a p i ta i s ac o m m o n l y u s e d i n d i c at o r o f e c o n o m i c d e v e lo p m e n t .In 1992 , t he GDP pe r c a p i t a i n C h i na wa s 470 US $a nd i n I t a l y i t wa s 21050 US $ (Ta b l e 5 ) . There l e va nc e o f a n e c onomi c a c t i v i t y t o t he na t i ona le c onomy c a n be a s se s se d by i t s c on t r i bu t i on t o t heGDP . In I t a l y (1992) , i n l a nd a qua c u l t u re a c c oun t e dfo r 0 .8% o f t he a g r i c u l t u ra l GDP . As a g r i c u l t u re


11/17

T . Gom iero e t a l . / Agr icu l tu re , Ec osys tems and Env iro nmen t 62 (1997 ) 169 -185 17 9T a b l e 5E c o n o m i c p e r f o r m a n c e a n d c o n t e x t o f a q u a c u l t u r e i n P R C h i n aa n d I t a l y ( 1 9 9 2 )

P R C h i n a I ta l yG D P p e r c a p i t a ( U S $ ) a 4 7 0 2 1 0 5 0P e r c e n t a g e o f G D P i n a g r i c u l t u r e b 2 8 . 4 3 . 2P e r c e n t a g e o f G D P i n a q u a c u l t u r e c 0 . 6 0 . 0 2 5P e r c e n t a g e o f t o t a l l a b o r f o r c e i n 6 5 7a g r i c u l t u r e bO p p o r t u n i t y c o s t o f l a b o r i n a g r i c u l t u r e 0 . 2 5 8(USSh ~)~

W o r l d T a b l e s , 1 9 9 5 .b W o r l d R e s o u r c e s I n s t i t u t e , 1 9 9 4 .

S e e t e x t f o r d e f i n i t i o n a n d c a l c u l a t i o n s .

a c c o u n t e d f o r 3 . 2 % o f t h e n a t i o n a l G D P ( T a b l e 5 ) ,i n l a nd a qua c u l t u re r e p re se n t e d a me re 0 .025% o f t hena t i ona l GDP . In C h i na (1992) , i n l a nd a qua c u l t u rea c c o u n t e d f o r 2 . 0 % o f t h e a g r i c u l t u r a l G D P ( Z h a o ,1994). A s a g r i c u l t u re a c c oun t e d fo r 28 .4% o f GD P(W or l d Ta b l e s , 1995) , i n l a nd a qua c u l t u re a c c oun t e df o r 0 . 6 % o f t h e n a ti o n a l G D P .

D i v i d i n g t h e G D P g e n e r a t e d b y a c o u n t r y i n ay e a r b y t h e l a b o r e m p l o y e d ( in h o u r s ) i n t h a t y e a r w eob t a i n a rough i de a o f t he a ve ra ge r e t u rn o f huma nl a bo r in t he c oun t ry . In t h is w a y , we f i nd fo r 1992 a na v e r a g e re t u rn o f l a b o r o f U S $ 0 . 4 3 h - 1 f o r C h i n aa nd U S $28 .50 h -1 fo r I t a l y ; a d i f f e re nc e o f moret ha n 66 t i me s .

In I t a l y , t he a dde d va l ue pe r worke r i n f r e shwa t e ra qua c u l t u re c a n be a s sume d t o be s i mi l a r t o t hea dde d va l ue pe r worke r i n a g r i c u l t u re (A . P e ro l o ,pe r sona l c ommuni c a t i on , 1996) . In 1992 , t h i s va l uewas about Li t ( I ta l ian l i re ) 19 .6 mi l l ion , orU S $ 1 4 0 0 0 ~ p e r w o r k e r p e r y e a r . T h e r e f o r e , t h ea m o u n t o f a d d e d v a l u e p e r w o r k e r i n a g r i cu l tu r e a n da qua c u l t u re wa s 35% l owe r t ha n t he na t i ona l a ve ra geG D P p e r c a p it a ( T a b l e 5 ). I f w e d i v i d e t h e a m o u n t o fa d d e d v a l u e p e r w o r k e r i n a g r i c u l t u r e ( U S $ 1 4 0 0 0 )b y t h e n u m b e r o f h o u r s w o r k e d o n a v e r a g e i n a y e a ri n t he s e c t o r ( = 1800) , we ob t a i n a n a ve ra ge r e t u rno f l a b o r i n t h at s e c t o r o f a lm o s t U S $ 8 h -

In C h i na , t he a dde d va l ue pe r worke r i n f r e shwa -t e r a qua c u l t u re ha s be e n e s t i ma t e d a t 232 0 , o r

U S $ 4 7 0 2 , pe r worke r pe r ye a r (Qi a n , 1994) . Th i sv a l u e m a t c h e s t h e a v e r a g e G D P p e r c a p i ta o f th ec oun t ry in 1992 (W or l d Ta b l e s , 1995). D i v i d i ng t h isn u m b e r b y t h e h o u r s w o r k e d i n a y e a r ( 1 8 0 0 ) , w eob t a i n a n a ve ra ge r e t u rn o f l a bo r o f a bou t US $0 .25h - 1 .

In I t a l y , a s i n o t he r de v e l ope d c oun t r i e s , t he re i s al a rge d i f f e re nc e be t we e n t he a dde d va l ue ge ne ra t e dpe r w orke r i n t he a g r i c u l t u ra l s e c t o r ( a nd i n a qua c u l -t u re ) a nd t he na t i ona l a ve ra ge . Of c ou rse , we c a nno te xpe c t t ha t a l l e mpl oyme n t oppor t un i t i e s i n a c oun-t ry p rov i de t he s a me re t u rn ( a nd s a me wa ge ) pe rhour . A c e r t a i n r a nge o f l a bo r p r i c e s , a round t hena t i ona l a ve ra ge r e t u rn , fo r d i f f e re n t t ype s o f l a bo r i si ne v i t a b l e . Howe ve r , t o a c h i e ve a n a c c e p t a b l e s t a n -da rd o f l i v i ng , t hose ( i n ou r c a se f a rme rs a nd work -e r s i n a qua c u l t u re ) wi t h wa ge s i n t he bo t t om pa r t o ft he r a nge mus t some how be a s s i s t e d t o r e a c h a ni nc ome t ha t i s r e a sona b l y c l o se t o t he a ve ra ge . In -deed, in prac t ice we f ind tha t the I ta l ian agr icul tura ls e c t o r , wi t h i t s r e l a t i ve l y poo r e c onomi c pe r fo r -ma nc e , r e c e i ve s gove rnme n t suppor t t o r a i s e t hei nc ome o f f a rme rs c l o se r t o t he a ve ra ge i n soc i e t y .

I n C h i n a , t h e e c o n o m i c p e r fo r m a n c e o f f i sh f a r m -ing and tha t of the agr icul tura l sec tor a re s imi la r tot he C h i ne se na t i ona l a ve ra ge , wh i c h i s ba s i c a l l y duet o t he l a rge pe rc e n t a ge o f t he l a bo r fo rc e e nga ge d i nagr icul ture .

The se da t a show why l a bo r p roduc t i v i t y i s af u n d a m e n t a l p a r a m e t e r i n e x a m i n i n g t h e e c o n o m i cfe a s i b i l i t y o f a ny fo rm o f p roduc t i on i n t he foodsys t e m. A h i gh opp or t un i t y c os t o f l a bo r i n a soc i e t yt r a ns la t e s i n t o the ne e d t o a c h i e ve h i gh l a bo r p rodu c -t i v i t y i n t he p roduc t i on p roc e s s (Gi a mpi e t ro , 1997) .In de v e l ope d c oun t r i e s , suc h a s I t a ly , t he a g r i c u l t u ra ls e c to r , t o w h i c h a qua c u l t u re i s c l o se l y r e l a t e d , s t rug -g l e s t o a c h i e ve a l a bo r p roduc t i v i t y t ha t p rov i de s a ni nc ome c ompa ra b l e t o t ha t a c h i e ve d i n t he r e s t o fsoc ie ty . This i ssue i s pa r t icula r ly re levant in I ta ly ,whe re a qua c u l t u re doe s no t r e c e i ve t he s a me e x t e n to f gove rnme n t a l p ro t e c t i on a s doe s a g r i c u l t u re(Melott i e t a l . , 1994).

J B a s e d o n t h e 1 9 9 2 e x c h a n g e r a te o f U S $ 1 b e i n g w o r t h L i t1 4 00 . 2 B a s e d o n t h e 1 9 9 2 e x c h a n g e r a t e o f U S $ 1 b e i n g e q u a l t o 5 .


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180 T. G omiero et al. // Agriculture, Ecosystems and Environment 62 (1997) 169 -185Table 6Per capita supply of energy and p rotein available for hum anconsumption in PR China and Italy in 1992a

PR China ItalyTotal food energy (kcal day - 1) 2734 3549Total protein (g day -1 ) 67.8 108.5% of total energ y from proteinb 9.9 12.2Animal protein (g day -t ) 16.4 58.2% of total protein (g g - i ) 24.2 53.6from anim al sourcesFish and sea food protein 2.7 6.2(g da y- i )c% of total protein (g g -I ) 4.0 5.7from fish and sea foodcFreshwater fish protein (g da y- t ) 1.3 0.4% of total protein (g g - ] ) 1.9 0.4from freshwater fishaSource:FAO , 1996.bUsing an e nergy conversion factor of 4 kcal g- i protein.Clncludes mari ne and fresh water products.5 .2 . R o l e o f f r e s h w a t e r f i s h i n f o o d s e c u r i ~

A c o m p a r i s o n o f t h e c o m p o s i t i o n o f t h e C h i n e s ea n d I t a l i a n f o o d s u p p l y a v a i l a b l e f o r h u m a n c o n -s u m p t i o n i n d i c a te s t h e e x i s t e n c e o f c o n s i d e r a b l e d i f -f e r e n c e s b e t w e e n t h e t w o c o u n t r i e s ( F A O , 1 9 9 6 )( Ta b le 6 ) .

I n C h ina , 24 . 2% o f t he to t a l da i ly p r o t e in c on -s u m e d i s f r o m a n i m a l s o u r c e s . F r e s h w a t e r f i s h a c -c o u n t s f o r 8 % o f t h e a n i m a l p ro t e i n c o n s u m e d a n d2 % o f t h e t o ta l p ro t e i n c o n s u m e d ( T a b l e 6 ) . T h er e l a t i v e l y l o w c o n s u m p t i o n o f t o t a l p r o t e i n , a n d i np a r t i cu l a r o f h i g h - q u a l i ty a n i m a l p r o t e i n , m a k e s t h ec o n t r i b u t i o n o f f r e s h w a t e r f i s h t o t h e C h i n e s e d i e ti m p o r t a n t i n p r o v i d i n g e s s e n t i a l a m i n o a c id s .

The s i t ua t ion in I t a ly i s ve r y d i f f e r e n t . To ta lp r o t e i n c o n s u m p t i o n i s w e l l o v e r 1 0 0 g d a y - ~ p e rc a p i t a , o f w h i c h 5 4 % i s f r o m a n i m a l s o u r c e s . F r e s h -w a t e r f i s h a c c o u n t s f o r o n l y 0 . 4 % o f t h e t o ta l p r o t e inc o n s u m p t i o n ( T a b l e 6 ) .

W h e n t h e i n t e r n a l r e q u i r e m e n t f o r f o o d e x c e e d sthe in t e r na l p r oduc t ion , a c oun t r y ne e ds to r e so r t t of o o d i m p o r t i n o r d e r t o a c h i e v e f o o d s e c u r i t y - - a tl e a s t w h e r e b a s i c f o o d i t e m s a r e c o n c e r n e d . F o o di m p o r t h a s t w o n e g a t i v e a s p e c t s : i t i m p l i e s d e p e n -de nc e on the in t e r na t iona l m a r ke t , a nd i t r e p r e se n t s ab u r d e n o n t h e n a t i o n a l e c o n o m y . I n C h i n a a n d I t a l y ,t h e e c o n o m i c a n d p o l i t i c a l p r e s su r e t o a v o i d r e c o u r s e

to f ood im por t s i s ve r y d i f f e r e n t . C h ina , w i th i t shuge popu la t ion ( 1 . 2 b i l l i on pe op le ) a nd r e l a t ive lyp o o r e c o n o m i c d e v e l o p m e n t , c a n n o t a f f o r d ( e c o -n o m i c a l l y ) t o r e l y h e a v i l y o n f o o d i m p o r t s ( l e a v i n ga s ide the de l i c a t e i s sue o f whe the r su f f i c i e n t su r p lu swou ld be a va i l a b l e on the in t e r na t iona l m a r ke t ) . Th i si s pa r t i c u l a r ly t r ue f o r h igh ly nu t r i t i ous f ood i t e m s( m e a t , f i sh , da i r y p r oduc t s ) t ha t a r e e xpe ns ive toim por t . I t i s t he r e f o r e o f s t r a t e g ic i n t e r e s t to C h in a tom a in ta in a nd s t r e ng the n f r e shwa te r f i sh p r oduc t ionb e c a u s e o f i ts i m p o r t a n t r o l e i n p r o v i d i n g h i g h - q u a l -i t y p r o t e in , a nd he nc e gua r a n te e ing f ood se c u r i ty .

I n I t a ly , on the o the r ha nd , f r e shwa te r f i sh p l a ys am a r g ina l r o l e i n t he d i e t , bo th f r om the nu t r i t i ona la n d t h e c u l t u r a l p o i n t o f v i e w . W h e n f r e s h w a t e ra q u a c u l t u r e i s n o l o n g e r e c o n o m i c a l l y r e w a r d i n g ,the n the r e i s no s t r a t e g ic i n t e r e s t i n e i t he r ke e p ing o rde ve lop ing th i s s e c to r . I n f a c t , i n 1996 , a bou t 35% o ft h e t r o u t p r o d u c t i o n ( w h i c h c o v e r s 2 4 % o f t o ta l f re s hf i sh p r oduc t ion ) wa s de s t ine d f o r spo r t f i sh ing , wh ic hi s a m o r e p r o f i t a b l e e n d t h a n t h e h u m a n f o o d m a r k e t( L . C o l o m b o , p e r so n a l c o m m u n i c a t i o n , 1 99 6; A .P e r o lo , pe r sona l c om m unic a t ion , 1996 ) . Th i s a l soe x p l a i n s t h e i m p o r t a n c e o f c o n s u m e r p r e f e r e n c e s i ns h a p i n g a q u a c u l t u r a l p r o d u c t i o n . H e r b i v o r o u ss p e c i e s , e v e n i f m o r e e c o l o g i c a l l y e f f i c i e n t , s i m p l yd o n o t h a v e a m a r k e t f o r h u m a n c o n s u m p t i o n i nI ta ly .

D a t a o n i m p o r t a n d e x p o r t o f f r e s h w a t e r f i s h f o rI t a ly a nd C h ina c on f i r m the se c ons ide r a t ions . I n1986 in I t a ly , t he r a t io t o t a l f i sh im por t / e xpo r t ( i nm o n e t a r y v a l u e ) e x c e e d e d 3 0 / 1 ( M e l o t t i e t a l . ,1 9 9 4) . I m p o r t s f r o m E u r o p e a c c o u n t e d f o r 7 0 % o fthe to ta l I ta l ian impor t (Melot t i e t a l . , 1994) . Forf r e s h w a t e r a n d l a g o o n f i s h t h e r a t i o i m p o r t / e x p o r t( in m one ta r y va lue ) wa s 4 /1 ( M e lo t t i e t a l . , 1994 ) .

W e f ind a ve r y d i f f e r e n t s i t ua t ion in C h ina , whe r ei m p o r t s o f a q u a t i c p r o d u c t s w e r e n e v e r r e p o r t e d t oe x i s t un t i l t he l a s t f e w ye a r s ( F AO, 1989 ; Q ia n ,1994). C h ine se e xpo r t s ( 1800 00 tons in 1986)r e a c he d 51 50 00 tons in 1992 , f o r a va lue o f US $1 . 7b i l l i on ( Q ia n , 1994 ) . I t shou ld be no te d tha t t he sev a l u e s a r e n e g l i g i b l e w h e n c o m p a r e d t o t h e s i z e o ft h e C h i n e s e e c o n o m y .5 .3 . D e m o g r a p h i c p r e s s u r e o n n a t u r a l r e so u r c e s

D e m o g r a p h i c p r e s s u r e i s a n i m p o r t a n t f a c t o r t h a tt h r e a t e n s t h e f o o d s e c u r i t y o f C h i n a t h r o u g h t h e


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T. Gom iero et al. / Agriculture, Ecosystems and Environment 62 (1997) 169-185 181c on t i nuous r e duc t i on o f a ra b l e l a nd a va i l a b l e pe rc a p i t a fo r food p roduc t i on . The a ra b l e l a nd i n Ch i nai s a bou t 0 .09 ha pe r c a p i t a (W or l d Re sourc e s In s t i -t u t e , 1994) , wh i c h i s muc h l owe r t ha n t he t h re sho l do f 0 .5 ha pe r c a p i t a i nd i c a t e d by some sc i e n t i s t s a st h e m i n i m u m r e q u i r e m e n t to g u a r a n t e e a v a r ie d f o o dsupp l y wi t hou t c a us i ng t o muc h e nv i ronme n t a l s t r e s s(La l , 1989; Kenda l l and P imente l , 1994) . S ince s ig-n i f ic a n t d e p e n d e n c e o n f o o d i m p o r t i s e c o n o m i c a l l y(a nd po l i t i c a l l y ) no t a f e a s i b l e s t r a t e gy fo r Ch i na i nt he ne a r fu t u re , t he h i gh de m ogra ph i c p re s su re ma k e sfoo d s e l f - su f f i c i e nc y a p r i ma ry a nd d i f f i c u l t goa l t oa c h i e ve .

P o p u l a t i o n p r e s s u r e m a y e x p l a i n w h y C h i n e s ef i sh pond c u l t u re i s c l o se l y i n t e g ra t e d i n t he f a rmi ngsys t e m (F AO , 1980a ; L i n , 1982 ; S ha n , 1987 ; Zhong ,1989 ; Luo a nd Ha n , 1990 ; Guo a nd Bra dsha w, 1993)a nd why a qua c u l t u re shou l d be c ons i de re d a n i n t e -gra l pa r t of agr icul ture (Lin , 1982) . F i rs t , Chinesei n t e g ra t e d fi sh f a rmi ng wa s de ve l ope d t o fu l l y u t i li z ethe sca rce na tura l resources ava i lable . I t s goa l i s toe s t a b li sh a huma n -ma na ge d s e l f - su f f i c ie n t e c osy s t e mwh e re wa s t e s a re r e c yc l e d t o i nc re a se t he food sup -p l y fo r t he pe op l e (S ha n , 1987) . As we l l a s f i shc u l t u re , wa t e r su r fa c e s a re u se d t o r a i s e ge e se a ndduc ks . P ond dyke s a re u se d fo r f ru i t t r e e a nd mul -be r ry c u l t i va t i on , a nd bo t t om s l ope s fo r fodde r c rops(S ha n , 1987 ; Zhong , 1989 , 1990) . In t he c ompl e xp o n d - d y k e s y s t e m i n th e P e a r l R i v e r d e l ta in s o u t h -e rn Ch i na , pon d a nd dyke a re t r e a t e d as a n i n t e g ra t e duni t (Zh ong , 1989, 1990) .

The c o n t i nuous e f fo r t t o i nc re a se t he p roduc t i v i t yo f na t u ral r e sou rc e s ha s s t i mu l a t e d the u se o f l ow-c os tfe e d i n Ch i na , suc h a s wa s t e f rom a g r i c u l tu re , a n i ma la n d h u m a n m a n u r e , w e e d s , a n d f e e d s o f l o w e c o -nom i c va l ue (L i n , 1982 ; S ha n , 1987 ; Zhong , 1992 ;L i a nd M a t h i as , 1994). A s t udy on c onve rs i o n ra t e so f ma nure i n f i sh b i oma ss r e po r t e d a r a t i o o f 8 .3 kgof ma n ure (d ry we i gh t ) t o ob t a i n 1 kg o f we t f ishweight (Zhu e t a l . , 1990) . From th is pe rspec t ive ,f r e shwa t e r a qua c u l t u re c a n be s e e n a s a n e f fe c t i veme t hod o f wa s t e r e c yc l i ng g i ve n t ha t a g r i c u l t u ra lwa s t e s r e p re se n t t he ma i n sou rc e o f f e e d fo r f i sh(Lin , 1982; Shan, 1987; Luo and Han , 1990; Zh ong ,1992 ; Guo a nd Bra dsha w, 1993) .

A s e c o n d r e a s o n w h y p o p u l a t i o n p r e s s u r e f a v o r sf re shwa t e r a qua c u l t u re c onc e rns t he op t i mi z a t i on o fsu r fa c e u se . The de ma nd o f l a nd fo r t he p roduc t i on

o f a n i ma l p ro t e i n is r e l a t i ve l y h i gh c o mp a re d t o p l a n tp ro t e i n . F o r i n s t a nc e , be e f p roduc t i on i n f e e d - l o t sba se d on i n t e ns i ve h i gh - i npu t f a rmi ng o f g ra i n s p ro -duc e l e s s t ha n 80 kg p ro t e i n pe r he c t a re o f c u l t iva t e dl a nd pe r ye a r (da t a r e fe r r i ng t o Ne w York S t a t e ,US A) (G i a mpi e t ro e t a l. , 1992) , whe re a s soybe a nsc a n p roduc e a bou t 900 kg c rude p ro t e i n pe r he c t a repe r ye a r (Be e t s , 1997) . Gi ve n t he sho r t a ge o f l a nd i nCh i na , a qua c u l t u re i s a n i n t e re s t i ng op t i on fo r p ro -duc i ng a n i m a l p ro t e i n a s i t u se s (wa t e r ) su r fa c e s t ha tdo no t d i r e c t l y c ompe t e wi t h p l a n t p ro t e i n p roduc -t i on . Ch i ne se pond f i sh f a rmi ng ha s a n a ve ra gep r o d u c t i o n o f 2 3 8 5 k g h a - 1 an d a p r o t e in p r o d u c t i o no f 190 kg ha -1 .

De mogra ph i c p re s su re i s a l so h i gh i n I t a l y , bu tno t a s s e ve re a s i n Ch i na . Abou t 0 .16 ha o f a ra b l el a nd a re a va i l a b l e pe r c a p i ta (W o r l d Re so urc e s In s t i -tu te , 1994) . However , l and ava i labi l i ty i s not asi mpor t a n t fo r food s e c u r i t y i n I t a l y a s i n Ch i na ,be c a use food i mpor t i s a f e a s i b l e op t i on . F o r i n -s t a nc e , i n 1989 i mpor t e d c e re a l s (ma i n l y f rom t heE u r o p e a n U n i o n ) c o v e r e d m o r e t h a n 3 0 % o f t h ein te rna l consumpt ion (Melot t i e t a l . , 1994) .

6 . D i s c u s s i o n

6 . 1 . D i f f e r e n c e s i n a q u a c u l t u r e p e r f o r m a n c e i n r e l a -t io n t o s o c i o e c o n o m i c c o n t e x t

The c on t r i bu t i on o f f r e shwa t e r a qua c u l t u re t o t hena t i ona l e c onomy i s ne g l i g i b l e bo t h i n Ch i na a ndI t a ly . Ye t t he re i s a n i m por t a n t d i f f e re nc e be t w e e nt he ro l e s o f a qua c u l t u re i n t he se t wo c oun t r i e s .W h e r e a s f r e s h w a t e r a q u a c u l t u r e i s c o m p l e t e l ymargina l in I ta ly , in China i t i s margina l only int e r m s o f t r a d e v o l u m e , b u t s t r a t e g i c a l l y i mpor t a n t i nb i ophys i c a l a nd e c onomi c t e rms .

In order to be poss ib le a t a l l , I t a l ian aquacul ture ,due t o i t s h i gh oppor t un i t y c os t o f l a bo r a nd c a p i t a l ,mus t be e c onomi c a l l y v i a b l e a t t he p roduc e r l e ve l .Th i s b a s i c p re re qu i s i t e is r e f l e c t e d in t he wi de sp re a da dop t i on o f i n t e ns i ve , a r t i f i c i a l monoc u l t u ra l sy s -t e ms , wh i c h ha ve a p roduc t i v i t y pe r hou r o f l a bo r( 2 0 - 8 0 k g h - 1 ) t h a t is m u c h h i g h e r t h a n t h a ta c h i e ve d i n Ch i ne se po l yc u l t u ra l sy s t ems (1 kg h - t )(Ta b l e 4 ) . Th e h i gh p rodu c t i on l e ve l in I t a l y de pe ndso n a c o m p l e t e c o n t r o l o f t h e r e a r i n g e n v i r o n m e n t


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1 8 2 T . G o m i e r o e t a l. / A g r i c u lt u r e , E c o s y s t e m s a n d E n v i r o n m e n t 6 2 ( 1 9 9 7 ) 1 6 9 - 1 8 5

th rough the use o f f eeds and wate r exchange , andim pl ies in tens ive use o f com m erc ia l energy , m ain lyin fo rm o f fos s il energy (T ab le 4 ).

Ch inese po lycu l tu ra l sys tem s , on the o ther hand ,r e ly m os t ly on the func t ion ing o f pond ecosys tem s .T hey r equ i r e a l im i ted inpu t o f com m erc ia l energy ,have a m uch sm al le r env i ronm en ta l im pac t , andreach a h igher e f f i c iency in the use o f na tu ra l re -sources . T h i s b iophys ica l pe r fo rm ance i s due to there l i ance o f the p roduc t ion p roces s on na tu ra l m ech a-n i sm s o f r egu la t ion o f aqua t ic ecosys tem s . However ,th i s dependence r ep resen t s a l im i t to the p roduc t iv i tytha t can be a ch ieved w i th th i s so lu t ion . By r e ly ing onpo lycu l tu ra l pond sys tem s , Ch inese p roducer s canincrease the na tu ra l ly occur r ing b iophys ica l e f f i -c iency to som e ex ten t , bu t can never r each a p roduc-t iv i ty ( th roughpu ts pe r hour and p er hec ta re ) typ ica lo f in tens ive m onoc u l tu ra l sys tem s .

T he r e la t ive ly poor econom ic per fo rm anc e o f Ch i -nese aquacul tural sys tems indicates that a fu turedeve lopm en t o f aquacu l tu re in deve loped coun t r i essuch as I t a ly in to the d i r ec t ion o f eco log ica l com pat i -b i l i ty and r a t iona l u se o f na tu ra l r esources w ou ld bedependen t on governm en ta l p ro tec tion po l ic ies guar -an tee ing econom ic suppor t . In the s am e way , therap id econom ic deve lopm en t o f Ch ina i s b r ing ingabou t f as t changes in the l eve l s o f l abor p roduc t iv i ty .Aquacul ture is not escaping th is t rend. The in tenseef fo r t under taken by the C h inese governm en t towarda genera l in tens i f i ca t ion o f the th roughpu t o f f i shp roduc t ion in aquacu l tu re (PR Ch ina M A, 1995) canvery wel l r esu l t in an abandon ing o f those eco log i -ca l ly ben ign charac te ri s ti c s typ ica l o f t r ad i tiona l pondpo lycu l tu re .6 .2 . T he e c o log ic a l v i e w

A com par i son o f the E l ton ian py ram id (py ram ido f v a l u e s o f b i o m a s s o r e n e r g y f l o w i n g a m o n g t r o p h icleve l s ) o f a typ ica l na tu ra l aqua t ic eco sys tem (F ig . 4 )w i th the pa t t e rn o f b iod iver s i ty use in Ch ina (F ig .3 (a )) shows tha t Ch inese p roducer s bas ica l ly r ep lacetop ca rn ivo res in the na tu ra l aqua t ic ecosys tem . Fu l -f i l l ing the ro le o f the upper com par tm en t o f theecosys tem , they t ake fu l l advan tage o f the na tu ra lp roces ses o f the conver s ion o f so la r and b iochem ica lenergy in to ed ib le b iom ass . Hence , in the Ch inesesys tem o f p roduc t ion the na tu ra l s t ruc tu re o f the

t r o u t

q~' ~ s m e l t

N s m a l le ~ c r u s t a c e a n s

p h y t o p l a n k t o n

I2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0

k c a l / m 2 / y e a rFig. 4. Ene rgy flow in a natural freshwater ecosystem (afterSchm itz, 1995).

aqua t ic ecosys tem p rov ides bo th the con t ro l o f en -e rgy and m at te r f lows , and a l a rge par t o f theneces sa ry inpu t s . In exchange , hum ans harves tb iom ass a nd p ro tec t the in teg r i ty o f the sys tem as awho le .

A com par i son o f the E l ton ian py ram id (F ig . 4 )with the pat tern of b iodivers i ty use in I ta l ian aqua-cul ture (F ig . 3(b)) shows the absence of any s imilar -i ty in shape. In the I ta l ian sys tem, the lower- levelcom pa r tm en ts a r e en t i r e ly m is s ing and the s i ze o f thetop ca rn ivo re com par tm en t i s huge .

T he l a rge com par tm en t o f top ca rn ivo res in theI ta l ian aquacu l tu ra l sys tem im pl ies the ex i s tence o f aco r respond ing huge com par tm en t o f phy top lank tonin an e x t e r n a l aqua t ic ecosys tem tha t i s exp lo i ted toconver t so la r energy in to f i sh b iom ass ( th rough na tu -ral cycl ing of nutr ients ) for use as feed ( the pel le ts )for the top carnivores in the aquacul tural sys tem. Thecho ice o f boos t ing the p roduc t iv i ty per hec ta re (o rper un i t o f vo lum e) in the fo rm o f in tens ive aquacu l-ture implies the use of p iscivorous species (morethan 80% of to tal product ion in I ta ly) that are (atleas t) two levels h igher in the t rophic chain thanphytoplankt ivorous species . (The la t ter species con-s t i tu te more than 60% of the to tal product ion inCh inese aquacu l tu re . ) T h i s cho ice i s pa id fo r by anincreased r equ i r em en t (hundreds o f t im es ) o f e x t e r -n a l ecosys tem ac t iv i ty per kg o f b iom ass p roduced( som e ecosys tem e l s ewhere has to p roduce the hugef low o f f ish used to m ak e f eed ) .

S ince in the ar t i f ic ial water body ( tank) used inI tal ian in tens ive aquacul ture al l t rophic levels but theupper one a re m is s ing , hum an m anagem en t m us ttake ca re o f (1 ) r egu la t ion o f the food inpu t r equ i r ed


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T . Gom iero e t a l . / Agr icu l tu re , E cosys tems and En v ironm en t 62 (1997 ) 169 -185 183

by t he c a rn i vo re s , (2 ) t he d i sposa l o f wa s t e s a nde xc e s s nu t r i e n t s , a nd (3 ) t he p rov i s i on o f a c on t ro lsys t e m t ha t s t a b i l i z e s a l l o t he r c ond i t i ons , suc h a sw a t e r q u a l it y a n d o x y g e n c o n t e n t.

Thus , no t on l y doe s i n t e ns i ve a qua c u l t u re i n I t a l ys ti ll d epe nd o n the ac t iv i ty of (exte rn a l ) na tura le c osys t e ms fo r t he p roduc t i on o f f e e d , bu t i t i s a l sof o r c e d t o c o n s u m e l a rg e a m o u n t s o f f o s s i l e n e r g y p e run i t o f food ou t pu t i n ma na g i ng t he sys t e m, r e l e a s ingi n t h i s p roc e s s a c ons i de ra b l e a moun t o f wa s t e i n t ot he e x t e rna l e nv i ronme n t . In o t he r words , be c a use o ft he p re s su re e xe r t e d by i t s soc i oe c onomi c c on t e x t ,I t a l i a n i n t e ns i ve a qua c u l t u re i s fo rc e d t o boos t t hep roduc t i v i t y o f t he a qua c u l t u ra l sy s t e m ( t a nk ) bysome how b r i ng i ng i n t he a c t i v i t y o f d i s t a n t a qua t i ce c osys t e m s ( i. e . ma r i ne e c osy s t e ms t ha t ge ne ra t e f ishme a l s u se d a s f e e d i npu t ) a nd by re p l a c i ng na t u ra lme c ha n i sms o f c on t ro l i n t he ha b i t a t . C l e a r l y , as i de -e f fe c t o f t h is i n t e ns i ve p roc e s s i s t he r e l e a se o fe f f l ue n t s i n t o t he e x t e rna l e nv i ronme n t . In f a c t , t hea r t i f i c i a l wa t e r body ( t a nk ) doe s no t ha ve t he r e c y -c l i ng c a pa b i l i t y o f t he a qua t i c e c osys t e m t ha t ge ne r -a t e d t he i mpor t e d fe e ds .

c onsumpt i on o f fo s s i l e ne rgy , a nd a c ons i de ra b l ee n v i r o n m e n t a l l o a d in g p e r u n i t o f p r o d u c e d b i o m a s s .

The se f i nd i ngs a re i n pe r fe c t a na l ogy wi t h t hosefound i n ge ne ra l fo r a g r i c u l t u ra l p roduc t i on t e c h -n i que s (Gi a mpi e t ro , 1997) . In c oun t r i e s whe re t hes o c i o e c o n o m i c c o n t e x t i m p o s e s h e a v y p r e s s u r e o nt h e s p e e d o f t h r o u g h p u t i n e x p l o i te d ' e c o s y s t e m s ' ,t he c on t ra s t be t we e n e c o l og i c a l a nd e c onomi c i n t e r -e s t s be c ome s t oo wi de . At t ha t po i n t , gove rnme n tpo l i c i e s a nd i n t e rve n t i ons a re r e qu i re d t o me d i a t eb e t w e e n t h e n e e d t o s o m e h o w p r e s e r v e a m i n i m u mof e c o l og i c a l c ompa t i b i l i t y a nd t he ne e d t o a c h i e vee c onomi c v i a b i l i t y . S uc h a me d i a t i on re qu i re s a ni n t e g ra t e d a s se s sme n t o f the pe r fo rm a nc e o f a qua c u l -ture us ing severa l pa ra l le l pe rspec t ives to re la te cos t sa nd be ne f i t s , e xp re s se d i n bo t h e c on om i c a nd e c o l og -i c al t e rms , t o the soc i oe c ono mi c c on t e x t i n wh i c ha qua c u l t u re i s pe r fo rme d . B i ophys i c a l a na l yse s o ft he t ype p ropose d i n t h i s pa pe r c a n re p re se n t a s t e pin th i s d i rec t ion .

Acknowledgements6.3. Linking dif ferent perspectives

T h e s p e e d o f t h ro u g h p u t o f p r o d u c e d b i o m a s s i s afunda me n t a l pa ra me t e r de f i n i ng t he ro l e a nd func t i ono f a q u a c u l t u re f o r t h e s o c i o e c o n o m i c s y s te m i n w h i c ht he a c t i v i t y t a ke s p l a c e . W he n t he t h roughpu t i ss l ow, t he ma i n ro l e o f a qua c u l t u re i s t o r e c ove ra g r i c u l t u ra l wa s t e s a nd use l ow-qua l i t y r e sou rc e s i nt he p roduc t i on o f h i gh -qua l i t y a n i ma l p ro t e i n . Thes l o w t h r o u g h p u t , b o t h p e r h o u r o f l a b o r a n d p e rhe c t a re , ma ke s i t pos s i b l e t o ma i n t a i n a s t ruc t u re o ft he ma na ge d sys t e m t ha t i s s i mi l a r t o t ha t o f na t u ra la qua t i c e c osys t e ms . Un de r t he se c ond i t i ons , a qua c u l-ture p lays a use ful ro le in in tegra t ing agr icul tura lp roduc t i on , r e c yc l i ng wa s t e s a nd by -p roduc t s , a ndc on t r i bu t i ng t o t he b i od i ve r s i t y a t l a ndsc a pe l e ve l .

W h e n t h e t h r o u g h p u t o f p r o d u c e d b i o m a s s i s f a st ,a qua c u l t u re me re l y ha s t he ro l e t o p roduc e h i gh -va l -ue d spe c i e s fo r s a l e on

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