Effects of Stocking Densities on Growth, Survival Rates, Productivity and Economic Return of Clam (Meretrix lyrata) Reared in Earthponds

Abstract

      Effects of stocking densities on the growth, survival rate and production efficiency of Meretrix lyrata commercial culture were investigated out in 500 square meter earth pond. Clam seeds (2.45±0.08g in body weight) were stocked at densities of 90, 150 and 210 individuals/m² and reared in a period of 12 months. Results showed that stocking densities did not affect the concentrations of DO, pH, NH4⁺ and chlorophyll-a in culture ponds (P>0.05). Growth rate (0.57-0.60 %/day) of clam reared at 90-150 individuals/m² was significantly (P<0.05) higher than that at 210 individuals/m² (0.48 %/day). In contrast. clam productivity was higher at stocking densities of 150-210 individuals/m² (26.4-27.0 ton/ha) than at 90 individuals/m² (18.8 ton/ha). Survival rates were inversely propotional to stocking

densities. The highest profit (138.6 million VND/ha) and benefit-cost ratio (32.13%) were observed at 150 individuals/m² and the lowest values (33.4 million VND/ha and 9.01%, respectively) at the density of 210 individuals/m². This study suggests that the suitable stocking density in the earth pond culture of M. lyrata should be is 150 individuals/m².