Evaluation of cottonseed [Gossypium sp] and soybean [Glycine max] meal as partial replacement for fishmeal in diets for juvenile Japanese flounder Paralichthys olivaceus

This study was conducted to investigate the effect of dietary supplementation of cottonseed and soybean meal (CS) on growth performance, feed utilization, and gossypol accumulation in juvenile (mean body weight 11 g) Japanese flounder Paralichthys olivaceus. Five isonitrogenous and isocaloric experimental diets (designated CS0, CS10, CS20, CS30, and CS40) containing 0, 10, 20, 30, and 40% CS mixture (1:1 w/w) were formulated. After 9 weeks of feeding trial, fish fed all diets did not show significant differences in growth performances, feed utilization, and whole body compositions. Hemoglobin content gradually decreased (P < 0.05) with increments of CS inclusion levels. There was a positive linear relationship between dietary gossypol and total liver gossypol contents. Free radical scavenging activity in the experimental diets gradually increased with increment of dietary CS inclusion. This finding indicates that the mixture of cottonseed and soybean meal with methionine and lysine supplementation could replace up to 40% of fishmeal protein in diets. However, 20% fishmeal protein replacement by dietary inclusion of cottonseed (9.4%) and soybean (8.7%) meal might be the optimum and safe level for the commercial use of CS in juvenile Japanese flounder.