Effect of dietary cottonseed meal on growth performance, physiological response, and gossypol accumulation in pre-adult grass carp, Ctenopharyngodon idellus

Cottonseed meal (CM) was used at up to 36.95% content in the diet (replacing 60% of dietary fish meal protein) without any negative effects on growth performance of pre-adult grass carp (initial body weight, 761 g) under outdoor conditions. A culture trial was conducted in net cages installed in a large concrete pond. Seven isonitrogenous and isoenergetic diets containing a gradient of CM concentrations (0, 12.2%, 24.4%, 36.6%, 48.8%, 54.8%, and 61.0%) as replacement for dietary fish meal protein (0, 20%, 40%, 60%, 80%, 90%, and 100%) were formulated. Dietary non-resistant starch (from maize) was inverse to dietary CM. Growth performance and feed utilization of fish fed the diets containing CM replacing 0-40% fishmeal protein were not affected after the 6-week feeding trial. Accumulation of hepatopancreatic total gossypol in the hepatopancreas was significantly correlated with free gossypol content in the diets (HTG=88.6+1.5xDFG, R-2=0.89, P<0.05). Intestinal alpha-amylase and gamma-glutamyl transpeptidase activities rose along with increasing dietary CM level. The structure of the mid-intestinal tissues and the ultrastructure of the enterocyte microvilli were normal when dietary CM was 36.6% (60% protein replacement). Increasing dietary CM content increased serum alanine aminotransferase levels but decreased serum alkaline phosphatase, cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglycerides, and albumin (P<0.05).