An 8-week feeding trial was conducted to evaluate the effects of fish meal (FM) replacement by rice protein concentrate (RPC) with supplementation of microcapsule lysine (ML) or crystalline lysine (CL) on growth performance, muscle development and flesh quality of blunt snout bream. Four isonitrogenous and isoenergetic diets were formulated, including FM diet (containing 50 g/kg FM), RPC diet (FM replaced by RPC), MRPC diet (FM replaced by RPC with ML supplementation) and CRPC diet (FM replaced by RPC with CL supplementation). Fish fed FM diet had significantly higher weight gain, feed efficiency, protein efficiency ratio and nitrogen and energy utilization than that of RPC group, but showed no statistical difference with other treatments. In addition, fish fed RPC diet showed higher muscle fibre frequency in the 20-to 50-μm class but lower >50-μm class and higher cooking loss than that of the other groups. Furthermore, no significant difference was found in whole-body proximate compositions, frequency distribution of <20-μm-diameter fibres, texture, muscle content, collagen, pH 24 hr post-mortem and sensory quality. The results showed that

This study aimed to investigate the effects of lysine supplement on the growth performance of blunt snout bream Megalobrama amblycephala fed diets with fish meal (FM) replaced by rice protein concentrate (RPC) with the potential mechanisms characterized. Fish were fed three diets, including the FM diet (containing FM), the RPC diet (FM replaced by RPC), and the MRPC diet (the RPC diet supplemented with lysine) for 8 weeks. Weight gain, protein efficiency ratio, and nitrogen and energy utilization of fish fed the FM diet were all significantly higher than those of the RPC treatment, but they showed no statistical difference with those of the MRPC group. Fish fed the RPC diet showed shorter villi length of the distal intestine than that of the other treatments. No significance was found in whole-body composition and intestinal and hepatic cell proliferation among all the treatments. However, fish fed the RPC diet obtained relatively low transcriptions of growth hormone (GH), GH receptor, insulin-like growth factor-I (IGF-I), target of rapamycin (TOR), ribosomal protein S6 kinase 1, myoblast determination protein, myogenic factor 5, and myostatin a (MSTNa) but high levels of eukaryotic translation initiation factor 4E-binding protein 2 (4E-BP2) than those of the other groups. Furthermore, little difference was found in the transcriptions of 4E-BP2, myogenin, muscle-specific regulatory 4, and MSTNb in muscle. Overall, these results showed that dietary supplement of lysine benefits the growth performance of blunt snout bream fed FM-free diets through the mediation of the GH-IGF-I axis, TOR signaling pathway, myogenic regulatory factors, and MSTN.

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