Evaluation of dietary vitamin B6 requirement of juvenile largemouth bass (Micropterus salmoides) on the basis of growth performance, transaminase activity, and nutrient metabolism

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For the determination of the dietary vitamin B 6 requirement of juvenile largemouth bass ( Micropterus salmoides ) and to study the impact of vitamin B 6 on their nutrient metabolism, the fish (1.66 ± 0.01 g) were fed 6 diets that measured vitamin B 6 contents of 2.03 (D1, control group), 2.91 (D2), 3.30 (D3), 6.03 (D4), 9.53 (D5), and 21.79 mg/kg (D6) for 12 weeks. The study demonstrated that in comparison to the control group, the final body weight (FBW), weight gain rate (WGR), and specific growth rate (SGR) were substantially increased in the D3, D4, and D5 groups, the viscerosomatic index (VSI) and hepatosomatic index (HSI) were increased in the D5 group, the feed conversion ratio (FCR) of the D4 group was markedly lower. Moisture of fish body decreased significantly with increasing dietary vitamin B 6 contents, while crude protein as well as crude lipid increased significantly in the D2, D5 and D6 groups. The enzyme activities of glutamic oxaloacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) were higher in the D5 and D6 groups, and the expression of got and gpt were markedly higher in the D4 and D5 groups, respectively. For protein metabolism , the expression of target of rapamycin ( tor ) and eukaryotic translation initiation factor 4E (eIF4E)-binding protein 1 ( 4ebp1 ) were significantly increased in the D5 group and the insulin-like growth factors −1 ( igf-1 ) mRNA up-regulated in the D5 and D6 groups. For lipid metabolism , the expression of fatty acid synthase ( fas ), acetyl-CoA carboxylase ( acc ), peroxisome proliferators–activated receptor-α ( ppar-α ) were increased in the D5 group. For glucose metabolism , the expression of glucokinase ( gk ), pyruvate kinase ( pk ) and glucose transporter 2 ( glut2 ) were increased in the D4 group. Based on FBW, FCR, GOT and GPT by quadratic regression analysis, the requirements of vitamin B 6 were 11.98, 12.73 mg/kg and 14.58, 14.17 mg/kg, respectively.