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

Abstract

This study aimed to investigate the optimal dietary vitamin B12 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±0.03g) were randomly assigned to six purified diets containing graded levels of vitamin B12 (0, 0.028, 0.051, 0.12, 0.23 and 0.41mg/kg) for 12weeks. Both weight gain (WG) and specific growth rate increased significantly (P<0.05) as dietary vitamin B12 levels increased from 0 to 0.051mg/kg, then plateaued with further increasing levels. Feed conversion ratio decreased as dietary vitamin B12 levels increased from 0 to 0.12mg/kg, but no statistical difference was observed. Whole-body composition and intestinal brush border enzymes activities also exerted little difference within the vitamin B12 range tested, whereas hepatic vitamin B12 contents increased remarkably (P<0.01) with increasing dietary vitamin B12 levels. Intestinal protease, amylase and lipase activities all increased significantly (P<0.05) as dietary vitamin B12 levels increased from 0 to 0.12mg/kg, but decreased remarkably (P<0.05) with further increasing vitamin B12 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 B12 levels. Based on the broken-line regression analysis of WG, the optimal dietary vitamin B12 requirement of fingerling blunt snout bream was estimated to be 0.06mg/kg. In addition, a supplementation of 0.12mg/kg vitamin B12 boosted intestinal digestive capability and hepatic IGF-I expression. Statement of relevanceThis study investigated the optimal dietary vitamin B12 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.