Effects of dietary Metschnikowia sp. GXUS03 on growth, immunity, gut microbiota and Streptococcus agalactiae resistance of Nile tilapia (Oreochromis niloticus)

Probiotic feeding is a new strategy of healthy fish farming. To examine the effects of adding Torulaspora sp. GXUS02 and Metschnikowia sp. GXUS03 on the growth and immune parameters of Nile tilapia, a feeding trial was conducted in this study using a feed dose of 10(8) CFU/g to cultivate tilapia (100 +/- 15 g) for 8 weeks. The growth performance, serum parameters, intestinal microbiota and the anti-Streptococcus agalactiae ability of tilapia were used to evaluate the effects of the yeast supplemented group. The results reveal that both yeast diets could significantly improve the growth performance of tilapia by significantly increased the activities of protease and xylanase. Amongst the serum parameters, the lysozyme activity and the amount of complement C3 and C4 of tilapia fed with GXUS03 were significantly increased, and the ability to fight Streptococcus agalactiae was significantly increased (p < 0.05). Both yeast diets could change the intestinal microflora structure of tilapia. GXUS02 could significantly increase the amount of Sarcina and significantly decrease the amount of Microdiscus. In the intestinal microbiota of tilapia fed with GXUS03, Golenkinia-longispicula and LD29 were significantly increased, whilst the amount of Microdiscus was significantly decreased. In the analysis of intestinal microbiota diversity of tilapia fed with two yeast diets for 30 and 60 days, the stability of the intestinal microbiota of tilapia was better. In conclusion, the addition of two kinds of yeast had a good probiotic effect on tilapia culture, and GXUS03 exhibited the best probiotic effect in promoting the growth and immunity of tilapia.