Optimal Dietary Protein Level for the White Shrimp (Litopenaeus vannamei ) in Low Salinity Water

In order to find the optimal dietary protein level for Litopenaeus vannamei in low salinity water, isolipid and isocaloric diets with different protein levels (25%, 30%, 35%, 40% and 45%) were tested to feed L. vannamei juveniles (mean weight 0.31 ± 0.02 g) for 56 days in salinity 2 g/L water. The results showed that: (1) as the dietary protein level increased, the final body weight, weight gain and specific growth rate increased at first and then decreased. In the 35% protein level group, significantly better results were obtained as compared to other groups (P<0.05). Through quadratic regression analysis of dietary protein level and weight gain and specific growth rate, we found that shrimps had the highest weight gain when dietary protein level was between 33.51%–34.35%; (2) as the dietary protein level increased, the shrimp moisture content decreased and the protein content increased while lipid and ash content did not significantly change; (3) as the dietary protein level increased, the activity of trypsin increased at first and then decreased, and the 35% protein level group had the highest trypsin activity, significantly higher than other groups (P<0.05). There were no significant differences in lipase or amylase activity.