Effect of dietary lipid level on growth performance, feed utilization and digestive enzyme of juvenile ivory shell, Babylonia areolate

A growth trial was conducted to evaluate the effects of dietary lipid levels on growth performance, feed utilization, carcass composition and digestive enzymes of juvenile ivory shell. Six isonitrogenous and isoenergetic experimental diets (43% crude protein and 15.46 kJ/g diet) using Pollack fish oil as the lipid source, were formulated to contain six lipid levels (1.83, 3.83, 5.91,7.80, 9.76 and 11.73% dry diet, respectively). Triplicate groups of 50 shells (average weight 160.50 ± 1.20 mg) were stocked in 120-l tanks and fed to apparent satiation twice daily for 10 weeks. The results showed that growth performance and feed utilization were significantly affected by dietary lipid levels (P < 0.05). Maximum weight gain, mean protein gain and specific growth rate occurred at 5.91% dietary lipid level (P < 0.05), soft body to shell ratios were not significantly difference above 3.83% dietary lipid level, and there were no significant differences (P < 0.05) in survival of ivory shell fed the experimental diets. There were significant difference in protein, lipid, moisture and ash content in soft body (P < 0.05). Lipid content in soft body positively correlated with dietary lipid level, however, protein and ash content in soft body significantly decreased with the increase in dietary lipid level. Pepsin activity in soft body significantly increased with dietary lipid level increasing from 1.83 to 7.80%, and trypsin-like enzyme activity significantly increased with increase in dietary lipid level from 1.83 to 5.91%. However, lipase activity in soft body increased with an increase in dietary lipid level, but amylase activity was not significantly affected by the dietary lipid level. The results of this trial indicated that dietary lipid levels above 7.80% dry matter did not improve growth performance or feed utilization of juvenile ivory shell. Quadratic regression analysis of mean protein gain against dietary lipid level indicated that the optimal dietary lipid requirement for maximum mean protein gain of juvenile ivory shell is about 6.54% of dry diet.