Combined effects of dietary fructooligosaccharide and Bacillus licheniformis on growth performance,body composition,intestinal enzymes activities and gut histology of triangular bream (Megalobrama terminalis)

This study was conducted to investigate the effects of fructooligosaccharide (FOS) and Bacillus licheniformis (B. licheniformis) on growth performance, body composition, intestinal enzymes activities and gut histology of Megalobrama terminalis. Nine experimental diets were formulated to contain three FOS levels (0, 3 and 6 g kg^?1) and three B. licheniformis levels (0, 1 and 5 × 10⁷ CFU g^?1) following a 3 × 3 factorial design. Accordingly, diets were named as 0/0, 0/3, 0/6, 1/0, 1/3, 1/6, 5/0, 5/3 and 5/6 (B. licheniformis/FOS). At the end of the 8‐week feeding trial, weight gain (WG) and specific growth rate (SGR) of fish fed 6 g kg^?1 FOS were both significantly (P < 0.01 and P < 0.05) higher than that of the other groups in terms of dietary FOS levels. Besides, WG and SGR of fish fed 1 × 10⁷ CFU g^?1 B. licheniformis were significantly (P < 0.05) higher than that of the control group in terms of dietary B. licheniformis levels. In addition, a significant interaction (P < 0.05) between dietary FOS and B. licheniformis was observed in finial weight, WG, SGR as well as the survival rate with the highest values all observed in fish fed diet 1/3. Hepatosomatic index, carcass lipid content, lipase activities as well as microvilli length increased significantly (P < 0.05) from 0 to 1 × 10⁷ CFU g^?1, but no significant difference (P > 0.05) was observed in terms of dietary FOS levels. In addition, a significant (P < 0.05) interaction of FOS and B. licheniformis was observed in both protease and Na⁺, K⁺‐ATPase activities with the highest value obtained in fish fed diet 1/3. The results indicated that the dietary applications of dietary FOS and B. licheniformis alone or in combination can significantly improve the growth performance, survival rate, intestinal enzymes activities as well as microvilli length of triangular bream. In addition, there is a significant interaction between dietary FOS and B. licheniformis. The best combination for this species is 3 g kg^?1 FOS with 1 × 10⁷ CFU g^?1 B. licheniformis.