Effects of dietary Lactococcus lactis Z-2 on growth, host health and resistance to Aeromonas hydrophila in juvenile common carp (Cyprinus carpio L.).

Background: Lactococcus lactis Z-2 was previously isolated from common carp intestine. In order to investigate the effects of optimal dose of L. lactis Z-2 on growth, host health and disease resistance to Aeromonas hydrophila in common carp, five experimental diets, including without (CK and CK+ groups) or with 5 × 10 (group A), 5 × 10 (group B) and 5 × 10 CFU g (group C) L. lactis Z-2, were evaluated for 8 weeks.

Results: Supplementation of L. lactis Z-2 increased final weights, weight gain, specific growth rate, condition factor and muscle crude protein content, while feed conversion ratio, muscle crude lipid and ash contents were lower than in the CK group (P < 0.05). Furthermore, L. lactis Z-2 also promoted intestinal digestive enzyme (lipase, amylase, protease) activities, improved intestinal morphology and upregulated gene (ZO-1, Occludin, Claudin) expression of intestinal barrier; stimulated secretion of proinflammatory (IL-6, IL-1β, TNF-α) and anti-inflammatory cytokines (TGF-β, IL-10) in serum; and boosted AKP, ACP, LZM and antioxidant enzyme (T-AOC, GSH-Px, T-SOD, CAT) activities of hepatopancreas (P < 0.05). Among them, the effect of group B was more prominent. After A. hydrophila infection, the CK+ group showed overexpression of immune indicators and decreased antioxidant capacity. Whereas dietary intervention with L. lactis Z-2 significantly reversed these changes. Moreover, the survival rate was significantly higher (100%) in group B than in the CK+ group (36.36%) after A. hydrophila infection (P < 0.05).

Conclusion: Dietary L. lactis Z-2 improved the growth performance, immune response, antioxidant capacity, intestinal health and disease resistance of juvenile common carp. Ultimately, 5 × 10 CFU g dietary L lactis Z-2 is recommended for the formulation of feed. © 2025 Society of Chemical Industry.