Dietary niacin requirement of juvenile blunt snout bream Megalobrama amblycephala based on a dose–response study

This study aimed to determine the optimal dietary niacin requirement of juvenile Megalobrama amblycephala . Fish, with an average weight of 3.62 ± 0.02 g, were randomly divided into six groups and fed six purified diets with graded levels of niacin (0, 10, 20, 30, 40 and 50 mg/kg) three times daily for 8 weeks. The survival rate, weight gain ( WG ), feed conversion ratio, protein efficiency and protein retention all significantly improved ( p  <   .05) as the dietary niacin level increased from 0 to 30 mg/kg but showed no significant difference ( p  >   .05) with further increases in niacin levels. The supplementation of 30 mg/kg niacin also led to a significant ( p  <   .01) reduction in the viscerosomatic index, hepatosomatic index and mesenteric fat index. The dietary niacin levels exhibited minimal effects on whole‐body moisture and ash content ( p  >   .05) but exerted a significant ( p  <   .05) influence on protein and lipid contents and liver nicotinamide concentrations with high values obtained in fish receiving greater than 30 mg/kg of niacin. In addition, moderate levels of niacin lowered plasma triglycerides, non‐esterified fatty acid and low‐density lipoprotein cholesterol concentrations ( p  <   .05). Based on the broken‐line regression analysis of WG and liver nicotinamide content, the optimal dietary niacin requirement of juvenile blunt snout bream was 31.25 and 30.62 mg/kg, respectively.