Effects of dietary exogenous xylanase supplementation on growth performance, intestinal health, and carbohydrate metabolism of juvenile large yellow croaker, Larimichthys crocea.

An 8-week feeding trial was conducted to evaluate the effects of dietary xylanase supplementation on growth performance, digestive enzyme activity, intestinal morphology parameter, intestinal microbiome diversity, and carbohydrate metabolism for juvenile large yellow croaker (Larimichthys crocea). Four levels of xylanase were added to basal diets (0, 600, 1200, and 1800 U kg-1). The results indicated that fish fed the 1200 U kg-1 xylanase diet had higher weight gain than those fed the 0 and 600 U kg-1 xylanase diet. The highest intestinal folds and microvillous height were observed at fish fed the 1200 U kg-1 xylanase diet. High-throughput sequencing revealed that the majority of reads derived from the large yellow croaker digesta belonged to members of Proteobacteria followed by Chloroflex, Bacteroidetes, Spirochaetae, and Firmicute. Supplementation of xylanase in diets increased the relative abundance of Bacteroides and Gemmatimonadete. The higher hepatic glucokinase (GK) and glucose-6-phosphate dehydrogenase (G6PD) activities were observed in fish fed the xylanase supplementation diet. Accordingly, dietary xylanase supplementation upgraded the relative expressions of gk and g6pd genes in liver. In conclusion, optimum dietary xylanase supplementation (600-1200 U kg-1) could improve the growth performance, optimize the intestinal morphology structure and microbiota constitution, and enhance the ability of carbohydrate utilization of juvenile large yellow croaker.