Effect of dietary cornstarch levels on growth performance, enzyme activity and hepatopancreas histology of juvenile red swamp crayfish, Procambarus clarkii (Girard)

An 8-week experiment was conducted to determine the ability of juvenile red swamp crayfish Procambarus clarkii (Girard) to utilize different levels of cornstarch. Seven isonitrogenous practical diets were formulated with different cornstarch levels (50, 100, 150, 200, 250, 300 and 350 g kg− 1). The growth indices, body composition, α-amylase activity and hepatopancreas histology were examined. Results showed that the survival ranged from 71.1% to 82.2%, and was not significantly affected by dietary cornstarch levels (P > 0.05). Feeding rate (FR) increased with the level of cornstarch (P < 0.05), with no significant differences among the groups fed with cornstarch over 250 g kg− 1 (P > 0.05). Weight gain (WG) and feed conversion ratio (FCR) were significantly affected by dietary cornstarch levels (P < 0.05), and the highest WG and lowest FCR were observed in the crayfish fed with the 200 g kg− 1 cornstarch diet. Crude lipid and hepatopancreas lipid content increased with increasing dietary cornstarch. A saturation curve was observed in the specific activity of the α-amylase, hemolymph glucose and hepatopancreas glycogen concentration in relation to dietary cornstarch levels, with the maximum activity in crayfish fed diets containing from 200 to 350 g kg− 1 cornstarch (P > 0.05). In addition, crayfish exhibited notable histological differences among the groups. The morphology of the hepatopancreas in crayfish fed with 150 g kg− 1 and 200 g kg− 1 was normal, with tubules tightly arranged. Different cell types in these two groups were well recognized and reasonably uniform in shape and size. It could be concluded that the optimum cornstarch level for this crayfish could be 203 g kg− 1 when the diets contain 350 g kg− 1 protein.