Feed-based Aeromonas hydrophila vaccine combined with plant-seed extracts improves immunity, growth, and disease resistance in Labeo rohita.

Major carps are economically important but highly susceptible to Aeromonas hydrophila infections. The overuse of antibiotics in aquaculture has led to antimicrobial resistance, highlighting the critical need for sustainable disease control strategies. This study evaluated the immunogenic potential of a feed-based formalin-inactivated vaccine combined with plant-seed extracts in Labeo rohita. Fish were acclimatized under laboratory conditions for two weeks. Then fish (weight 6.50 ± 0.04 g) were randomly allocated into six groups: T0 (control group); T1 (ASE); T2 (RSE); T3 (AV); T4 (AV + ASE) and T5 (AV + RSE) with triplicates for eight weeks. Growth, hematological and immunological parameters were assessed, followed by challenge test with A. hydrophila (106 CFU/mL). The outcomes showed that, among treatments the vaccine combined with herbal extract (T4) significantly (p < 0.05) enhanced growth, zootechnical performance and hematological indices including RBCs, Hb and Hct levels. Highest thrombocytes were observed in T5 group. Lysozyme activity was highest (p < 0.05) in T4, indicating enhanced immune response. Microscopic examination revealed qualitative differences in intestinal morphology among the treatment groups. During post challenge period, the positive control exhibited severe clinical signs, including erratic swimming, tail-fin rot, scale damage and anemia. However, the severity of clinical signs and mortality were significantly reduced in fish from T3, T4, and T5 compared to the other groups, indicating greater protection against bacterial infection. Following the challenge trial, the highest survival rates were observed in T4 (90%) and T5 (85%), corresponding to Relative Percent Survival (RPS) values of 87.5% and 81.25%, respectively. Post-challenge hematological analysis revealed a decline in RBCs, Hb, and Hct levels, whereas WBCs and thrombocytes increased, reflecting an active immune response. These findings demonstrate that the feed-based vaccine, particularly with herbal extracts, can induce innate immunity offering a safe, effective, and eco-friendly strategy for controlling bacterial infections in aquaculture and a sustainable alternative to antibiotics.