SINGLE OR CONJOINT ADMINISTRATION OF LACTIC ACID BACTERIA ON THE GROWTH AND IMMUNE RESPONSE OF MICROPTERUS SALMOIDES

In this study, we aimed to evaluate the individual and combined effects of Lactiplantibacillus plantarum LP-37 (GenBank No. OP824883) and Pectiococcus pentosus PP-23 (GenBank No. OP824884) on the growth and immune response of largemouth bass (Micropterus salmoides). There were four experimental groups: C0, T1, T2, and T3. Fish were fed with a basal diet (C0) supplemented with 1.0×10⁸ CFU/g of LP-37 (T1), 1.0×10⁷ CFU/g of PP-23 (T2), and a combination of 1.0×10⁸ CFU/g of LP-37+1.0×10⁷ CFU/g of PP-23 (T3) for 6 weeks. Each group had three replicates, 50 fish per replicate. The results indicated that the final body weight, weight gain, and specific growth rate in T1—T3 were significantly higher than those of the C0 group (P<0.01), while the feed conversion ratio was significantly lower (P<0.05). Notably, the T3 group exhibited the most pronounced growth promoting effects. The villus height in T1 and T3 groups was significantly higher than that of fish in C0 group (P<0.01), and the villus width in T3 group was significantly higher than that in C0, T1, and T2 groups (P<0.05). The muscle layer thickness in T1—T3 group was also significantly higher than that in the C0 group (P<0.05). Furthermore, single or conjoint administration of lactic acid bacteria resulted in elevated levels of three serum enzymes and intestinal digestive enzyme activity in largemouth bass, with the LP-37+PP-23 combination yielding the higher levels. Comparing with the C0 group, IL-1β, IL-8, TNF- α, and IFN-γ mRNA expression levels in the spleen and head kidneys of T1—T3 group significantly decreased (P<0.05), while expression levles of IL-10 and TGF-1β significantly increased (P<0.05). Hence, supplementation with LP-37 and PP-23 additives significantly improve the growth, enzyme activity in the serum and intestine, increased expression of anti-inflammatory factors, decreased expression of pro-inflammatory factors, and significantly improved the intestinal morphology in largemouth bass. Moreover, the probiotic effect of LP-37+ PP-23 was particularly effective.