Trimethylamine N-oxide promotes the growth of Chinese mitten crab (<i>Eriocheir sinensis</i>), deposition of amines, and activates the mTOR pathway by affecting metabolism of amino acids

This study was conducted to evaluate the changes in amino acid metabolism and amine deposition in Chinese mitten crab (<italic>E. sinensis</italic>) fed with a diet containing Trimethylamine N-oxide (TMAO) to promote its growth and flavor. Three diets containing 0% TMAO, 0.01% TMAO, and 0.04% TMAO were designed respectively for <italic>E. sinensis</italic> (37.50 ± 0.5 g) for 15 weeks. According to the results, two experimental groups with TMAO had significant decrease in feed conversion ratio and feed intake (<italic>p</italic> &lt; 0.05) while it showed the opposite trend in the enzyme activity of trypsin. With the addition of TMAO, the value of umami in muscle increased significantly (<italic>p</italic> &lt; 0.05). Compared with the other two groups, the 0.04% TMAO group showed a significant increase in TMAO deposition and the content of methionine in the muscle (<italic>p</italic> &lt; 0.05). Meanwhile, the deposition of spermidine and spermine significantly decreased in this group (<italic>p</italic> &lt; 0.05). When feeding crabs with the diet containing 0.01% TMAO, the relative gene expression of <italic>S6K1</italic> and <italic>eIF4E</italic> increased significantly while <italic>4E-BP1</italic> decreased markedly (<italic>p</italic> &lt; 0.05). The protein expression of mTOR in muscle showed an upward trend in the 0.01% TMAO group. In summary, 0.01% TMAO in the diet could improve the FCR by increasing the enzyme activity of trypsin and improving growth performance by activating the mTOR pathway. 0.04% TMAO could increase the value of umami and the deposition of TMAO in muscle.