Effects of dietary methionine on growth performance and metabolism through modulating nutrient-related pathways in largemouth bass (Micropterus salmoides)

Methionine (Met) as molecular signaling plays a vital regulatory role in growth-related cellular functions. However, more research in the regulatory mechanism of Met in fish species is needed. Therefore, this study was designed to elucidate the regulatory role of dietary Met on body growth performance and metabolism. Largemouth bass (initial body weight: 4.10 ± 0.01 g) fed with control (CON, Met: 1.21 % of diet) diet and Met deficiency (MD, Met: 0.93 % of diet) diet, respectively for 8 weeks. Results of present study showed that compared with the MD diet (specific growth performance: 3.01 ± 0.03 %/d; weight gain ratio: 438 ± 9.16 %), control diet significantly increased the specific growth performance (3.36 ± 0.02 %/d) and weight gain ratio (557 ± 7.41 %), respectively (P < 0.05). Moreover, the fish fed with control diet also had higher feed efficient ratio and protein efficiency ratio (1.12 ± 0.01; 2.28 ± 0.01) than the fish fed with MD diet (0.88 ± 0.03; 1.83 ± 0.05). Mechanically, present study demonstrated that Met supplementation increased the amino acid (AA) concentrations through improving transport efficiency of AA transporters. Elevated AA concentrations promoted systemic nutrient sensing by activating the growth hormone-insulin-like growth factor (GH-IGF) signaling pathway. Activated GH-IGF signaling then up-regulated the target of rapamycin (TOR) signaling and suppressed the amino acids response (AAR) signaling. Up-regulated TOR and down-regulated AAR caused by Met supplementation acted together to increase the nutrient metabolic level, which further accelerate the growth performance. Our study better explained how fish through nutrient sensing signaling to coordinating growth and metabolism in response to dietary Met availability