Dietary taurine supplementation can improve the growth, protein metabolism, immunity and muscle development of larval largemouth bass (Micropterus salmoides)

This study aimed to explore the impact of dietary taurine supplementation on the growth, amino acid transport, protein metabolism, immunity, and muscle and skeletal development of larval largemouth bass (Micropterus salmoides). The larvae (initial weight: 367.53 ± 0.05 mg) were fed with six graded levels of dietary taurine (0 % (control group), 0.15 %, 0.3 %, 0.6 %, 1.2 %, and 2.4 %) for 21 days, which was sufficient for the duration of feeding trial of fish larvae. Results indicated that the weight gain rate and specific growth rate (SGR) of larvae showed a quadratic increase after dietary taurine supplementation (P < 0.05), reaching a maximum in the 0.3 % group. The protease activity was significantly enhanced by 0.3 % of dietary taurine (P < 0.05). The crude protein and amino acid content in the larvae were increased with taurine supplementation, peaking at 0.3 % (P < 0.05). The average myofiber diameter was also significantly enhanced in the 0.3 % group (P < 0.05). Compared to the control group, the supplementation of 0.3 % dietary taurine could upregulate the expressions of amino acid transport protein genes (P < 0.05). The TOR pathway was triggered by 0.3 % of dietary taurine. The AAR, autophagy-lysosome, ubiquitin-proteasome, and calpain pathways were inhibited by 0.3 % dietary taurine. The expressions of myocyte proliferation-related genes (such as Pax3a, MHC, MyoD) and MyoD protein, and Mstn were significantly increased and decreased by dietary taurine, respectively (P < 0.05). In addition, the mRNA levels of skeletal development-related genes were upregulated. Furthermore, dietary taurine supplementation upregulated anti-inflammatory and anti-apoptotic gene expressions, and reduced pro-inflammatory and apoptotic factor expressions in the liver. In summary, dietary taurine enhanced intestinal protein digestion and amino acid absorption, facilitated muscle protein deposition and myofiber development, and improved immunity and skeletal growth, thereby promoting growth in larval largemouth bass. Regression analysis based on the SGR revealed that the optimal taurine supplementation level was 0.288 %.