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Effects of dietary tryptophan levels on growth performance, whole body composition and gene expression levels related to glycometabolism for juvenile blunt snout bream, Megalobrama amblycephala

Ji, K., Liang, H., Chisomo‐Kasiya, H., Mokrani, A., Ge, X., Ren, M., Liu, B.
Aquaculture nutrition 2018 v.24 no.5 pp. 1474-1483
Megalobrama amblycephala, body composition, carboxy-lyases, dietary protein, feed conversion, feed intake, fish, gene expression, gene expression regulation, glucokinase, glucose-6-phosphatase, growth performance, insulin-like growth factor I, juveniles, lipid content, liver, messenger RNA, protein efficiency ratio, regression analysis, tryptophan, weight gain
To investigate the effects of dietary tryptophan on growth and glycometabolism in juvenile blunt snout bream, 450 fish (initial weight 23.33 ± 0.03 g) were fed six practical diets with graded levels of tryptophan (from 0.79 g/kg to 5.96 g/kg dry matter) for 8 weeks. Results showed that final weight, per cent weight gain (PWG), protein efficiency rate, feed intake and feed conversion ratio (FCR) were significantly improved by 2.80 g/kg diet. The maximum values of protein and ash were observed in 2.80 g/kg diet, while moisture was minimum. Lipid content of fish fed 3.95 g/kg diet was significantly higher than other diets. The highest plasma insulin‐like growth factor‐1 (IGF‐1) content was observed in 0.79 g/kg diet. In the liver, IGF‐1 mRNA levels were significantly downregulated by 2.80 g/kg dietary tryptophan, while glucokinase levels were by 3.95 g/kg, while glucose‐6‐phosphatase and phosphoenolpyruvate carboxykinase mRNA levels showed a converse trend compared with IGF‐1. Based on PWG and FCR, the optimal dietary tryptophan level was determined to be 1.99 g/kg (6.20 g/kg of dietary protein) and 1.96 g/kg (6.11 g/kg of dietary protein), respectively, using broken‐line regression analysis.