Effects of two fish-derived probiotics on growth performance, innate immune response, intestinal health, and disease resistance of Procambarus clarkii

Selection of the appropriate strain for particular aquatic animals is necessary for the desirable benefits of pro-biotics application in aquaculture, however, it is not very clear whether fish-derived probiotics could provide beneficial effects on invertebrates. In the present study, two fish-derived probiotics, Bacillus amyloliquefaciens, and Lactococcus lactis, were administrated as feed additives for crayfish (Procambarus clarkii) at concentrations of 10(6), 10(7), and 10(8) CFU/g for 28 days, respectively. Then their effects on the growth performance, innate immune enzyme activity, immune-related genes expression, haemocyte phagocytic activity, intestinal microbial diversity, and pathogen resistance of crayfish were evaluated. The results showed that the final weight, weight gain (WG), and specific growth rate (SGR) were significantly higher in 108 CFU/g B. coagulans and L. lactis additive groups. Compared to the control group, the activities of immune-related enzymes (acid phosphatase, alkaline phosphatase, glutathione peroxidase, and lysozyme) in the intestine were significantly increased in most of the probiotics added groups. In almost all experimental groups, the mRNA expression of two AMP genes (PcALF3 and PcAst) was enhanced in the intestinal of crayfish, and the expression level was proportional to the amounts of probiotics used. Moreover, the intestinal of crayfish in probiotics groups have better integrity and a thicker mucosal layer, and higher density granules in epithelial cells were also observed. According to the results of next -generation sequencing technologies, the diversity of intestinal microbiota in crayfish was also increased after supplementation with B. coagulans or L. lactis. Finally, the phagocytosis rate of haemocytes and pathogen resistance has also been improved. Taken together, our results suggested that fish-derived probiotics have beneficial effects on crayfish, and they can be treated as potential feed additives in practical applications.