Effects of dietary carbohydrate levels on growth performance, feed utilization, liver histology and intestinal microflora of juvenile tiger puffer, Takifugu rubripes

An 8-week feeding trial was conducted to investigate the effects of dietary carbohydrate levels on growth performance, body composition, and plasma biochemical parameters, liver and gut histology, and intestinal microbiota of Takifugu rubripes. Five isonitrogenous and isolipidic experimental diets were formulated with graded levels of cassava starch: 0% (C0), 8% (C8), 16% (C16), 24% (C24), and 32% (C32). The results showed that weight gain rate, specific growth rate (SGR) and protein efficiency ratio significantly increased in C16 and C24 groups (P < 0.05), while the feed conversion ratio expressed an opposite trend. Feeding rate is decreased with the increasing of carbohydrate levels (P < 0.05). Liver lipid content was dramatically increased in C24 treatment (P < 0.05). The intestinal amylase activity and muscle glycogen content were higher than other groups (P < 0.05). Plasma glucose levels were increased in C24 and C32 groups (P < 0.05). In addition, the abundance of intestinal potentially pathogenic bacteria (Staphylococcus) decreased, and the intestinal probiotics (Lactobacillus) increased with the increasing of dietary carbohydrate level (P < 0.05). The intestinal bacteria, indicated by Sobs, Chao and Shannon indexes, were more diverse with the increasing of the carbohydrate level (P < 0.05), meanwhile the abundance of transport and metabolism of carbohydrate, lipid and amino acid were enhanced with the increasing of carbohydrate levels (P < 0.05). In conclusion, appropriate supplementation of carbohydrate in diet promoted growth performance and feed utilization of juvenile Takifugu rubripes, and increased the liver lipid and muscle glycogen content, as well as intestinal microbial diversity. Based on the quadratic regression between SGR and carbohydrate levels, the optimal dietary carbohydrate level of juvenile Takifugu rubripes is 21.6%.