Effects of dietary methionine on growth performance, muscle nutritive deposition, muscle fibre growth and type I collagen synthesis of on-growing grass carp (Ctenopharyngodon idella)

In the current research, a 60-d experiment was conducted with the purpose of exploring the impacts of methionine (Met) on growth performance, muscle nutritive deposition, muscle fibre growth and type I collagen synthesis as well as the related signalling pathway. Six diets (iso-nitrogenous) differing in Met concentrations (2 center dot 54, 4 center dot 85, 7 center dot 43, 10 center dot 12, 12 center dot 40 and 15 center dot 11 g/kg diets) were fed to 540 grass carp (178 center dot 47 (SD 0 center dot 36) g). Results showed (P < 0 center dot 05) that compared with Met deficiency, optimal level of dietary Met (1) increased feed intake, feed efficiency, specific growth rate and percentage weight gain (PWG); (2) increased fish muscle protein, lipid and free amino acid contents and improved fish muscle fatty acid profile as well as increased protein content in part associated with the target of rapamycin complex 1 (TORC1)/S6K1 signalling pathway; (3) increased the frequency distribution of muscle fibre with >50 mu m of diameter; (4) increased type I collagen synthesis partly related to the transforming growth factor-beta 1/Smads and CK2/TORC1 signalling pathways. In conclusion, dietary Met improved muscle growth, which might be due to the regulation of muscle nutritive deposition, muscle fibre growth and type I collagen synthesis-related signal molecules. Finally, according to PWG and muscle collagen content, the Met requirements for on-growing grass carp (178-626 g) were estimated to be 9 center dot 56 g/kg diet (33 center dot 26 g/kg protein of diet) and 9 center dot 28 g/kg diet (32 center dot 29 g/kg of dietary protein), respectively.