Dietary vitamin B12 requirement of fingerling blunt snout bream Megalobrama amblycephala determined by growth performance, digestive and absorptive capability and status of the GH-IGF-I axis

This study aimed to investigate the optimal dietary vitamin B-12 requirement of fingerling blunt snout bream Megalobrama amblycephala based on the results of growth performance, intestinal digestive and absorptive capability and responses of the growth hormone (GH)-insulin-like growth factor -I (IGF-I) axis. Fish (initial body weight: 0.71 +/- 0.03 g) were randomly assigned to six purified diets containing graded levels of vitamin B-12 (0, 0.028, 0.051, 0.12, 0.23 and 0.41 mg/kg) for 12 weeks. Both weight gain (WG) and specific growth rate increased significantly (P < 0.05) as dietary vitamin B-12 levels increased from 0 to 0.051 mg /kg, then plateaued with further increasing levels. Feed conversion ratio decreased as dietary vitamin B-12 levels increased from 0 to 0.12 mg /kg, but no statistical difference was observed. Whole -body composition and intestinal brush border enzymes activities also exerted little difference within the vitamin B-12 range tested, whereas hepatic vitamin B-12 contents increased remarkably (P < 0.01) with increasing dietary vitamin B-12 levels. Intestinal protease, amylase and lipase activities all increased significantly (P < 0.05) as dietary vitamin B-12 levels increased from 0 to 0.12 mg, kg, but decreased remarkably (P < 0.05) with further increasing vitamin B-12 levels. Similar results were also observed in hepatic IGF-I expressions. Furthermore, the mRNA expressions of GH in the brain decreased significantly (P < 0.05) with increasing dietary vitamin 812 levels. Based on the broken -line regression analysis of WG, the optimal dietary vitamin 812 requirement of fingerling blunt snout bream was estimated to be 0.06 mg/kg. In addition, a supplementation of 0.12 mg/kg vitamin B-12 boosted intestinal digestive capability and hepatic IGF-I expression. Statement of relevance: This study investigated the optimal dietary vitamin B-12 requirement of fingerling blunt snout bream based on growth performance. The underlying mechanisms were also investigated with emphasis on intestinal digestive and absorptive capability and modulation of the GH-IGF-I axis. Data obtained here might facilitate the development of low-cost formulated feed for aquatic species. (C) 2016 Elsevier B.V. All rights reserved.