Optimal dietary pyridoxine requirement of juvenile blunt snout bream, Megalobrama amblycephala

This study was conducted to determine the optimal dietary pyridoxine requirement of juvenile blunt snout bream Megalobrama amblycephala. Eight hundred and forty fishes average initial weight:(6.810.17) g were fed with seven isonitrogenous and isoenergetic diets containing different pyridoxine levels (0, 1.04, 1.99, 4.07, 5.91, 7.96 and 9.22 mg/kg) 3 times daily for 8 weeks, respectively. Each diet was tested in four replicates, and each replicate had 30 fishes. Weight gain (WG), specific growth rate (SGR), feed conversion ratio (FCR), survival rate, protein efficiency ratio (PER) and nitrogen retention efficiency (NRE) were all increased significantly (P0.05) as dietary pyridoxine levels increased from 0 to 5.91 mg/kg. PER and NRE were all decreased significantly (P0.05) with further increase of pyridoxine levels, but WG, SGR and FCR showed no significant difference (P0.05). No significant difference (P0.05) was observed both in condition factor and dressout percentage among all the treatments, while hepatosomatic index was significantly (P0.05) affected by dietary pyridoxine levels. The lowest value was observed in fish fed with 5.91 mg/kg pyridoxine. Liver glutamic-pyruvic transaminase (GPT) and glutamic-oxalpacetate transaminase (GOT) activities and pyridoxine contents all increased significantly (P0.05) as dietary pyridoxine levels increased from 0 to 5.91 mg/kg. However, they all showed no significant difference (P0.05) with further increase of pyridoxine levels. On the basis of the broken-line analysis of hepatic GOT and GPT activities and liver pyridoxine contents against dietary pyridoxine levels respectively, the optimal dietary pyridoxine requirement of juvenile blunt snout bream was estimated to be 4.175.02 mg/kg.