COMPARATIVE STUDIES ON CULTURAL EFFICIENCY AND PROFITS OF DIFFERENT POLYCULTURAL SYSTEMS IN PENAEID SHRIMP PONDS

Comparative studies on ecological efficiency , production and economic profit s of different polyculture sy stems of Chinese shrimp (Penaeus chinensis Osbeck)w ith red Taiw an tilapia (Oreochromis mossambicus × O .ni lot icus), bay scallop (Argopecten irradians), common sea-perch (Lateolabrax japonicus)and constricted tagelus(S inonovacula constricta)as aux iliary members separately in closed seawater ponds were conducted by using 50 land-based enclosures of each 5 .0 × 5 .0 ×1 .8m in 1996 .In result s , the nit rogen conversion efficiencies by the animals cultivated , the polyculture systems were ranged in a descending order as :“common sea-perch -Chinese shrimp -tilapia polyculture”(PST)(30 .91 %)>“Chinese shrimp-bay scallop polyculture”(SBS)(21 .01 %)>“ex tensive Chinese shrimp-tilapia polyculture” (STM)(20 .12 %) >“intensive Chinese shrimp-tilapia poly culture” (STF)(17 .81 %)>“Chinese shrimp-const ricted tagelus polyculture” (SCC )(16 .93 %)>monoculture of Chinese shrimp (S)(11 .52 %), suggesting that ecological efficiencies of the poly culture sy stems were higher than those of the monoculture ones .By ratio of output to input , the polyculture sy stems were ranged in a descending order as :S TF (1 .99)>STM (1 .98)>SBS(1 .53)>S(1 .38)>PS T(1 .30)>SSC (1 .23).While by the net incomes (×104 yuan RMB/hm2), the polyculture sy stems w ere ranged in a descend order as :PST(2 .57)>S TF (1 .62)>SSC(0 .91)>STM(0 .81)>SBS(0 . 76)>S (0 .54).All the results indicate that polyculture of the shrimp w ith tilapia , bay scallop or const ricted tagelus is characterized by bet ter benef it than monoculture is .