Abstract
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 (2·54, 4·85, 7·43, 10·12, 12·40 and 15·11 g/kg diets) were fed to 540 grass carp (178·47 (SD 0·36) g). Results showed (P < 0·05) 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 µm of diameter; (4) increased type I collagen synthesis partly related to the transforming growth factor-β1/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 9·56 g/kg diet (33·26 g/kg protein of diet) and 9·28 g/kg diet (32·29 g/kg of dietary protein), respectively.
Highlights
Methionine (Met) is an essential amino acid for grass carp Ctenopharyngodon idella[1]
There may be some relationship between Met and muscle growth associated with muscle fibre and type I collagen as well as potential transforming growth factor-β1 (TGF-β1)/Smads and target of rapamycin complex 1 (TORC1) signalling in fish, which deserves research
We discovered that the optimal level of Met enhanced the feed intake, feed efficiency, percentage weight gain (PWG) and the activities of glutamate-oxaloacetate transaminase and glutamate-pyruvate transaminase in the hepatopancreas and muscle as well as decreased the plasma ammonia content of on-growing grass carp, indicating that Met improved amino acid utilisation and growth performance of fish
Summary
Methionine (Met) is an essential amino acid for grass carp Ctenopharyngodon idella[1]. In fish muscle, it has been reported that Met increased protein and lipid deposition in juvenile grouper Epinephelus coioides[7] and promoted muscle fibre hypertrophy in juvenile rainbow trout Oncorhynchus mykiss[3]. These studies lack systematicity and rarely explore involved mechanisms. The main collagen in intramuscular connective tissue is type I collagen[14], the expression of which is regulated by the transforming growth factor-β1 (TGF-β1)/Smads signalling pathway at the transcriptional level[15]. There may be some relationship between Met and muscle growth associated with muscle fibre and type I collagen as well as potential TGF-β1/Smads and TORC1 signalling in fish, which deserves research
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