An Experimental Study on Structure Optimization for Polyculture of Grass Carp with different Species

This research was designed to find out the best polyculture mode of grass carp ponds. The outputs, total cost vs gross receipt and synthetic efficiency index of different ecosystems, in which Ctenopharyngodon idellus, Hypophythalmichthys molitrix, Cyprinus carpio and Litopenaeus vannamei cultured in different mono- and poly-culture treatments, were studied in land-based enclosures. There were six treatments: grass carp treatment (G); grass carp and silver carp treatment (GS); two treatments stocked grass carp, silver carp and common carp with different proportion (GSC1 and GSC2); two treatments stocked grass carp, silver carp and vannamei with different proportion (GSL1 and GSL2). The results indicated that the water quality objectives of poly-culture were better than G treatment; the Chl.a of G treatments were higher than other treatments. The results of single factor analysis of variance and Duncan multiple comparison analysis showed that the difference among each treatment was significant (P0.05). The net output of grass carp ranged from 3738.09 kg/hm2 to 6548.30 kg/hm2 and the survival rates ranged from 98.67% to 100%; the net output of silver carp ranged from 1097.28 kg/hm2 to 3391.84 kg/hm2 and the survival rates ranged from 87.88% to 100%; the net output of common carp ranged from 1975.51 kg/hm2 to 2828.57 kg/hm2 and the survival rates were 100% totally; the net output of shrimp ranged from 718.80 kg/hm2 to 958.10 kg/hm2 and the survival rates ranged from 40.96% to 47.17%; the total outputs of ecosystem ranged from 7704.80 kg/hm2 to 11492.50 kg/hm2; the net outputs ranged from 6548.30 kg/hm2 to 9958.50 kg/hm2, the G treatment was the lowest and GSC1 treatment was the highest, and the difference between each treatment was significant (P0.05). The feed coefficient ranged from 1.00 to 1.38, GSC1 treatment was the lowest and GSL2 treatment was the highest, and the difference between each treatment was significantly (P0.05). The total N input ranged from 372.56 kg/hm2 to 421.90 kg/hm2; the total P input ranged from 34.40 kg/hm2 to 38.96 kg/hm2; the total relative utilization rates of N and P ranged from 2.01 to 7.37, G treatment was the lowest and GSL2 treatment was the highest, and the difference between each treatment was significant (P0.05). The total costs of each treatment were ranged from 4.77104￥/hm2 to 6.15104￥/hm2; the total benefits were ranged from 7.32104￥/hm2 to 12.61104￥/ hm2; the total cost vs gross receipt ranged from 1:1.41 to 1:2.12, the G treatment was the lowest and the GSL2 treatment was the highest, the difference between each treatment was significant (P0.05). The synthetic efficiency index ranged from 0.59 to 1.39, the G treatment was the lowest and the GSL2 treatment was the highest, and the difference between each treatment was significant (P0.05). The results showed that poly-culture could obviously improve outputs of ecosystem, reduce feed coefficient, increase utilization rates of N and P, and finally raise economic and ecological benefits of ecosystem. The conclusion could be made that the GSC1 and GSL2 treatments were better than other treatments, and the stocking density of GSC1 as that: grass carp, 69.39 g/m2, silver carp, 20.75 g/m2 and common carp, 54.08 g/m2 ; the stocking density of GSL2 as that: grass carp, 69.39 g/m2, silver carp 56.46 g/m2 and vannamei, 14.80 g/m2.