Effects of replacing live bait with compound feed on growth, digestion and expression of small peptide transporter(PepT1) gene of Siniperca chuatsi

【Objective】To compare the differences in growth performance, digestive function and expression of PepT1 gene in intestine of Siniperca chuatsi fed by live bait and compound feed, and clarify the physiological changes of digestion and absorption after feeding compound feed, and provide theoretical basis for improving the utilization effect of compound feed for S.chuatsi.【Method】A total of 300 individuals with feeding domestication(average initial weight of 5.92±1.41 g) and 300 individuals without feeding domestication(average initial weight of 6.06±1.73 g) were selected and fed with compound dietand live bait fish for 30 d respectively.The growth performance, muscle composition, structure of digestive tract, digestive enzyme activity and small peptide transporter(PepT1) gene expression were determined and analyzed after feeding.【Result】The final mean body weight, total food intake, average individual feed intake, feed coefficient, daily gain, daily gain, special growth rate, protein efficiency, survival rate and fatness of the compound feed group were extremely significantly lower than thoseof the live bait group(P< 0.01, the same below), while the organbody weight ratio and liver-body weight ratio were significantly higher than thoseof the live bait group(P< 0.05, the same below).The muscle composition of live bait fish was obviously affected by feeding compound feed instead of live bait.The moisture content of muscle was extremely significantly lower than that of the live bait group, and the crude protein content of muscle was significantly higher than that of the live bait group, when compound feed replacedlive bait to feed.In terms of digestive enzyme, activity of trypsin in the pyloriccaecum in the feed group were extremely significantly lower than that in the live bait group, and that of lipase were significantly lower than that in the live bait group, but there was no significant difference in digestive enzyme activity of liver and intestine(P> 0.05, the same below).Loose liver cells were observed in compound feed group, the fat accumulation among liver cells was detected, the thickness of stomach, intestinal muscle layer and gastric submucosa in the compound feed group was extremely significantly lower than those in the live bait group.The number of goblet cell in single villuswas extremely significantly more than that in live bait group, and the fold spacing of pyloric caecum was extremely significantly higher than that in the live bait group.The relative expression level of gene PepT1 in the intestine of each group was foregout> midgut> hindgut, and the expression level in foregut of compound feed group was extremely significantly lower than that in the live bait group, but there was no significantly difference in the midgut and hindgut.【Conclusion】Feed intake and utilization of compound feed are lower than those of live bait fish, and the structure of the digestive tract, digestive enzymes activity also change adaptively due to the compound feed, and it significantly affects the function of digestion and absorption and growth performance.Thus, it is necessary to further improve the nutritional components of feedor optimize the domestication technology of S.chuatsi according to its feeding and metabolic characteristics.