This study aimed to investigate the effects of dietary tryptophan (Trp) on growth performance and muscle quality of Procambarus clarkii. Six experimental diets with graded Trp concentrations (0.05%, 0.13%, 0.29%, 0.43%, 0.56%, 0.69%; designated Trp0.05 to Trp0.69) were fed to crayfish for 8 weeks. Growth parameters, muscle proximate composition, texture, histology, related gene expression, and intestinal microbiota were measured. Compared with the Trp0.05 group, the Trp0.43 group significantly increased FW, WGR, SGR, and muscle crude protein content, while decreasing FCR. It also improved muscle texture (hardness, springiness, cohesiveness, gumminess, chewiness), increased muscle fiber diameter, and reduced fiber density and the proportion of fibers < 30 μm. Additionally, the Trp0.43 group upregulated mRNA expression of MEF2A, MEF2B, MLC1, MyHC, mTOR, S6K1, AKT, LARP6, Col1α1, Col1α2, TGF-β1, and Smad, and downregulated MSTN, 4EBP1, FOXO, and LC3. It reduced Proteobacteria and Shewanella abundance, and increased Bacteroidota and Firmicutes. In conclusion, appropriate dietary Trp improves P. clarkii growth, muscle quality, and intestinal microbiota. Based on quadratic regression analysis of WGR and SGR, the dietary Trp requirement of P. clarkii was estimated to be 0.39%, corresponding to 1.22% of feed protein.
Chen et al. (Fri,) studied this question.