Integrative unveiling of optimum dietary protein requirement for Siniperca scherzeri: Growth performance, feed utilization, serum biochemical and immune parameters and hepatic health maintenance

To determine the optimum protein requirement of Siniperca scherzeri, this study was conducted to investigate the effects of dietary protein levels on the growth performance, feed utilization, serum biochemical and immune indices as well as hepatic health for Siniperca scherzeri. Five isolipidic diets were formulated containing 38.13 % (P38), 41.16 % (P41), 45.12 % (P45), 49.13 % (P49), 53.07 % (P53) protein levels, respectively, and fed to 375 Siniperca scherzeri (initial weight: 75.42 ± 0.45 g) for 8 weeks. Results showed that the survival rate (SR) of fish fed with the P38 diet was significantly lower than that of other groups. The maximum weight gain rate (WG, 88.84 %), specific growth rate (SGR, 1.13 % day−1), protein efficiency ratio (PER, 1.18) and the best feed conversion ratio (FCR, 1.74) were recorded in fish fed with P49 diet. Serum biochemical parameters demonstrated that low-protein diet (P38) might cause disturbance of lipid metabolism [decreased triglycerides (TGs), total cholesterol (TC), low density lipoprotein-cholesterol (LDL-C) and high density lipoprotein-cholesterol (HDLC) concentration] and protein metabolism [decreased total protein (TP) and increased ammonia as well as urea nitrogen (UN) concentration], and liver impairment [increased alanine aminotransferase (ALT) activity]. Additionally, we found that an increment of dietary protein level (P49 and P53 diets) significantly enhanced body non-special immunity [increased lysozyme (LZM) concentration]. Moreover, results about hepatic health maintenance suggested that an increment of dietary protein level improved antioxidant ability [increased catalase (CAT) activity and total antioxidant capacity (T-AOC), and decreased malonyl dialdehyde (MDA) content] and abnormal lipid accumulation [decreased lipid droplet and TGs content] in the liver of Siniperca scherzeri. Besides, we found that an increment of dietary protein level significantly suppressed the processes of inflammation response, cell apoptosis and autophagy in the liver of Siniperca scherzeri. Cubic regression analysis suggested that the optimal protein requirements of Siniperca scherzeri were 49.82 % ∼50.79 %, based on WG, SGR, PER and FCR. The present study provides new insights into the optimal dietary protein requirements of Siniperca scherzeri and establishes a theoretical basis for formula compound feed of Siniperca scherzeri in the future [Display omitted] •Determination of optimum dietary protein requirement of Spinibarb