Effect of IgY antibody coated fish feed in preventing motile Aeromonas septicaemia in Ctenopharyngodon idella: a histopathological perspective

Aeromonas hydrophila is an opportunistic bacterial pathogen responsible for motile Aeromonas septicaemia (MAS), a major disease affecting freshwater aquaculture species such as Ctenopharyngodon idella (Grass carp). The conventional use of antibiotics to control bacterial infections has led to several adverse outcomes, including antibiotic resistance, drug residues in fish tissues, and environmental pollution. The present study aimed to develop and evaluate the efficacy of immunoglobulin Y (IgY) antibodies as an alternative therapeutic and preventive measure against A. hydrophila infections. The median lethal concentration (LC₅₀) of A. hydrophila, determined through immersion challenge, was 1.5 × 10⁷ CFU/ml. Fish feed coated with 3.5–5% IgY was administered to experimental groups, resulting in survival rates ranging from 65% to 100%. The therapeutic, neutralisation, and vaccination efficacies of IgY treatment were observed to be 60%, 70%, and 80%, respectively. Histopathological examinations revealed that IgY-treated fish showed minimal pathological alterations in the skin, gills, small intestine, and large intestine compared to antigen-treated and control groups. The results demonstrate that oral administration of IgY-coated feed effectively reduces A. hydrophila infections and related tissue damage. This study highlights IgY as a promising, environmentally friendly immunotherapeutic alternative to antibiotics in aquaculture, offering a sustainable approach for disease prevention and management in C. idella culture systems.