Effects of dietary taurine level on growth, fat metabolism, and non-specific immunity of Mandarin fish (Siniperca chuatsi)

Taurine is a conditionally essential amino acid, and the ability to synthesize taurine in carnivorous fish is often missing or insufficient. Siniperca chuatsi is a unique and precious variety in China. Under natural conditions, the S. chuatsi needs live fish for food from its birth. In recent years, with the maturity of artificial domestication technology, artificial compound feed has been widely used to cultivate S. chuatsi in China. As a typical carnivorous fish, the article on its demand for taurine has not been reported. To determine the optimal level of taurine in S. chuatsi feed and its effects on the growth, fat metabolism and non-specific effects of S. chuatsi, five groups of iso-nitrogen and iso-lipid feeds with different levels of taurine were prepared, which were 0.36% (Tau1), 0.84% (Tau2), 1.35% (Tau3), respectively. 1.88% (Tau4) and 2.39% (Tau5) were fed with the initial body weight of (68.81±0.82) g for 12 weeks. The results showed that with the increase of dietary taurine level, the weight gain rate (WGR), specific growth rate (SGR), and protein efficiency (PER) were firstly increased and then decreased, and the feed coefficient (FCR) was firstly decreased and then increased. The WGR, SGR and PER of S. chuatsi in Tau3 group were the highest, FCR was the lowest, and the crude protein content of whole body and muscle was significantly increased, while the crude lipid content of liver was significantly decreased. With the increase of dietary taurine level, serum low-density lipoprotein (LDL) content first decreased and then increased, and reached the lowest level in Tau3 group. High density lipoprotein (HDL) content increased first and then decreased, and reached the highest level in Tau2 group. Serum triglyceride (TG) content decreased with the increase of taurine level. The mRNA expression of srebp1, acc1, fas, lpl and hsl related to fat metabolismin the liver of S. chuatsi was significantly enhanced by the addition of appropriate amount of taurine in the diet. Serum lysozyme (LZM) and alkaline phosphatase (AKP) contents increased first and then decreased with the increase of taurine level, and reached the highest in Tau3 group. The expression of proinflammatory cytokines il-1β, pai and tnf-α genes was significantly inhibited by the appropriate increase of dietary taurine level. In conclusion, the addition of appropriate amount of taurine in feed can significantly promote the growth performance and body protein deposition of S. chuatsi, promote fat metabolism and enhance the non-specific immunity of S. chuatsi. According to the broken line regression analysis of dietary taurine level and fish body weight gain rate, the maximum growth of S. chuatsi, was achieved when the dietary taurine level was 1.3%. This study may provide a new idea to solve the problem of hepatobiliary syndrome in the process of feed culture of S. chuatsi, and at the same time provide a certain theoretical basis for healthy farming of S. chuatsi and the improvement of feed formula.