Optimizing Aeromonas hydrophila vaccine efficacy in common carp: The role of free vs. microencapsulated Lactiplantibacillus plantarum and Lactobacillus delbrueckii bulgaricus.

Abstract

This study investigated the effects of two probiotics, Lactiplantibacillus plantarum (L. plantarum) and Lactobacillus delbrueckii bulgaricus (L. bulgaricus), administered orally either in free form or microencapsulated with alginate/chitosan, on the immunogenicity and protective efficacy of an Aeromonas hydrophila vaccine in common carp (Cyprinus carpio). A total of 540 fish (mean weight: 48&#xa0;&#xb1;&#xa0;5.1&#xa0;g) were randomly allocated into six experimental groups: vaccinated control (A), vaccinated&#xa0;+&#xa0;free L. plantarum (B), vaccinated&#xa0;+&#xa0;encapsulated L. plantarum (C), vaccinated&#xa0;+&#xa0;free L. bulgaricus (D), vaccinated&#xa0;+&#xa0;encapsulated L. bulgaricus (E), and unvaccinated control (F). Growth indices, immunohematological parameters, intestinal enzyme activity, antioxidant status, and serum biochemistry were analyzed on days 0, 30, and 60 of the experiment. On day 60, each group was challenged with A. hydrophila, and mortality was monitored for 14 days. The results demonstrated that fish receiving encapsulated probiotics (Groups C and E) exhibited significantly higher survival rates compared with the other groups, along with markedly improved growth performance (FCR, SGR, PER, FER) and intestinal enzyme activity (lipase, protease, amylase, ALP). Probiotic-supplemented groups showed significantly enhanced immune responses, evidenced by increased antibody titers, lysozyme activity, nitroblue tetrazolium (NBT) reduction, complement activity, globulin concentrations, and myeloperoxidase activity (P&#xa0;<&#xa0;0.05). These immunological enhancements occurred without significant changes in hematological parameters or serum biochemical profiles, which remained statistically similar across groups (P&#xa0;>&#xa0;0.05). Mortality following the challenge was lowest in Groups C and E (20&#xa0;% vs. 80&#xa0;% in the control group). In conclusion, microencapsulated L. plantarum and L. bulgaricus enhanced vaccine efficacy and immunogenicity more effectively than free probiotics. Alginate/chitosan encapsulation is therefore recommended as an efficient delivery system to optimize probiotic supplementation and vaccine performance in carp aquaculture.