Effects of Lactobacillus plantarum and Bacillus subtilis on growth, immunity and intestinal flora of largemouth bass(Micropterus salmoides)

Probiotics play a crucial role in largemouth bass aquaculture, primarily in enhancing water quality, preventing fish diseases, promoting largemouth bass growth, and boosting immunity in high-density culture conditions. The experiment was actualized by adding Lactobacillus plantarum, Bacillus subtilis and a mixture of probiotic (L. plantarum and B. subtilis 1:1) in the culture water of largemouth bass for 42 days, respectively, to explore the effect of the above two probiotics on the growth performance and immunity ability of largemouth bass (Micropterus salmoides). Results: At the level of phylum, the relative abundance of enteric flora in Tenericutes of largemouth bass in L. plantarum added group was significantly higher than that in control group (p < 0.05). Conversely, the relative abundance of Proteobacteria was significantly lower than that of control group (p < 0.05). Similarly, at the genus level, the relative abundance of Mycoplasma and Leifsonia was significantly higher than that of control group (p < 0.05), while the relative abundance of Aeromonas was significantly lower in the L. plantarum added group compared to the control group (p < 0.05). Compared with the control group, there were no significant differences in phylum level in the B. subtilis added group (p < 0.05), and the relative abundance of Plesiomonas was significantly increased (p < 0.05), the relative abundance of Aeromonas was significantly decreased at genus level (p < 0.05). The relative abundance of Plesiomonas and Parabacteroides in the mixed probiotic treatment group was significantly increased (p < 0.05), the relative abundance of Aeromonas was significantly decreased at the level of genus (p < 0.05). The metabolites of carboxylic acid and its derivatives, organic oxygen compound, glycerophospholipid, lip acyl and other categories in enteric tissues of all treatment groups had significant changes (p < 0.05), enteric bacterial secondary metabolites such as SCFAs and 1-Phosphatidyl-D-myo-inositol were significantly increased (p < 0.05). The results showed that the addition of L. plantarum and B. subtilis in water could promote the growth of largemouth bass and increase its nonspecific immunity by enhancing the stability of enteric flora, increasing efficiency of enteric digestion and absorption and promoting the anti-inflammatory and immune ability of the body through secondary metabolites of enteric microbe.