Dietary Pyridoxine And Thiamin Requirement Of Juvenile Blunt Snout Bream, Megalobrama Amblycephala

This study was conducted to determine the effects of dietary pyridoxine and thiamin levels on growth performance, body composition, physiological and biochemical parameters of juvenile blunt snout bream Megalobrama amblycephala, in order to provide theoretical basis for optimizing the feed formula for this species.This study included three experiments:Experiment 1 Dietary pyridoxine requirement of juvenile blunt snout bream, Megalobrama amblycephalaThis study was conducted to determine the optimal dietary pyridoxine requirement of juvenile blunt snout bream Megalobrama amblycephala. Fish (average initial weight: 6.81±0.17 g) were fed 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 fish. Weight gain (WG), specific growth rate (SGR), feed conversion ratio (FCR), survival rate, protein efficiency ratio (PER) and nitrogen retention efficiency (NRE) all increased significantly (P<0.05) as dietary pyridoxine levels increased from 0 to 5.91 mg/kg. PER and NRE all decreased significantly (.P<0.05) with the further increasing pyridoxine levels, but WG, SGR and FCR showed no significant difference (P>0.05). No significant difference (P>0.05) was observed both in condition factor and dressout percentage among all the treatments, while hepatosomatic index was significantly (.P<0.05) affected by dietary pyridoxine levels with the lowest observed in fish fed 5.91 mg/kg pyridoxine. Liver glutamic-pyruvic transaminase (GPT) and glutamic-oxalpacetate transaminase (GOT) activities and pyridoxine contents all increased significantly (P<0.05) as dietary pyridoxine levels increased from 0 to 5.91 mg/kg. However, they all showed no significant difference (P>0.05) with the further increasing pyridoxine levels. Based on 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 4.17-5.02 mg/kg.Experiment 2 Effects of dietary pyridoxine on digestive enzyme activities, antioxidation and immune responses of juvenile blunt snout bream, Megalobrama amblycephalaThis study was conducted to evaluate the effects of dietary pyridoxine on digestive enzyme activities, antioxidation and immune response of juvenile blunt snout bream, Megalobrama amblycephala. The conceptual design was the same as that of the first experiment. The results indicated that when the level of dietary pyridoxine was higher than 4.07 mg/kg, the intestinal lipase activity was significantly improved (P<0.05), but no significance difference (P>0.05) was observed both in intestinal protases and amylase activities. The hepatic superoxide dismutase (SOD) activity increased significantly (P<0.05) and malondialdehyde (MDA) activity decreased significantly (P<0.05) as dietary pyridoxine levels increased from 0 to 5.91 mg/kg, while glutathione peroxidase (GPX) activity showed no significant difference. Plasma total protein content reached the maximum value and was significantly higher than other treatments when the dietary thiamin level was 5.91 mg/kg. When the dietary thiamin level was 5.91 mg/kg, the plasma albumin was the higest, but no significant difference was observed in all the treatments (P>0.05). The alkaline phosphatase activity all increased as dietary pyridoxine levels increased from 0 to 7.91 mg/kg. However, they all showed no significant difference (P>0.05) with the pyridoxine levels. The lysozyme activity has the same trend with the alkaline phosphatase activity. Therefore, the optimal level of dietary pyridoxine could improve digestive enzyme activities, antioxidation and immune response of juvenile blunt snout bream, Megalobrama amblycephala.Experiment 3 Dietary thiamin requirement of juvenile blunt snout bream, Megalobrama amblycephalaThis study was conducted to determine the optimum thiamin requirement of juvenile blunt snout bream Megalobrama amblycephala (average initial weight:0.3 g). Fish were fed six isonitrogenous and isoenergetic diets containing different thiamin levels (0,0.51, 0.98,1.59,2.13, and 2.68 mg/kg) 3 times daily for 8 weeks. Each diet was tested in four replicates, and each replicate had 30 fish. Weight gain (WG) and final weight (FW) all increased significantly (P<0.05) and feed convention ratio (FCR) decreased significantly (P<0.05) as dietary pyridoxine levels increased from 0 to 1.59 mg/kg. But WQ FW and FCR showed no significant difference (P>0.05) with the further increasing pyridoxine levels. No significant difference (P>0.05) was observed in survival rate among all the treatments. The level of plasma glucose was sinaficantly (P<0.05) affected by dietary thiamin levels with the lowest observed in fish fed 1.59 mg/kg thiamin, but plasma pyruvate and lactate showed no significant difference (P>0.05). The liver thiamin content had an increasing trend with the incease of dietary pyridoxine (from 0 to 1.59 mg/kg). Based on the broken-line analysis of weight gain and hepatic thiamin content against dietary pyridoxine levels, the optimal dietary thiamin requirement of juvenile blunt snout bream was estimated to be 1.48-1.84 mg/kg.