Optimal dietary animal to plant protein ratio for the pacific white shrimp, Litopenaeus vannamei at two salinities.

Protein is one of the most important components in crustacean diets,which should be optimally utilized to achieve faster growth rate of the cultured animals.To enable the preparation of a cost-effective feed at the farm level,the ratios of protein derived from the various animal and plant sources in the feed need to be optimized.In this study,the factorial effects of ambient salinity and animal to plant protein ratio on growth and survival of juvenile white shrimp,Litopeneaus vannamei were investigated.Six diets were formulated using soy protein concentrated and fish meal as plant and animal protein sources respectively,of which the dietary animal to plant protein ratios were 0∶38,7∶30,14∶23,21∶16,29∶8 and 36∶0 approximately.Each diet was fed to three replicate groups of shrimp for 40 d.The results showed that dietary animal to plant protein had significant effects on the shrimp weight gain,hepatosomatic index(HSI),conditional factor,survival rate and the hepatopancreas soluble protein.Weight gain increased when the dietary animal to plant protein ratio increased,while for other indexes measured,they exhibited the tendency of increased first with the dietary animal to plant protein ratio increasing,and then decreased slightly.Increasing salinity significantly increased the weight gain,survival and the conditional factor,and significantly decreased shrimp HSI,while no significant differences of salinity were observed in shrimp HSI.Shrimp weight gain,survival and HSI were significantly affected by the interaction between ambient salinity and dietary animal to plant protein ratio,while shrimp conditional factor and the hepatopancreas were not significantly affected by the interaction between ambient salinity and dietary animal to plant protein ratio.Combined,the results in this study indicate that dietary amino acids content and profile would change with the change of dietary animal to plant protein ratio,and though L.vannamei has different demand for protein,it could be met by regulating dietary animal to plant protein ratio in the practical diets.The Broken-line model analysis showed that the optimal dietary animal to plant protein content in the diets for the white shrimps at the salinity of 3.0 and 22.0 ranged from 29.12∶7.79 to 30.29∶6.71 and from 26.05∶10.95 to 29.03∶7.437 approximately.