IMMUNE RESPONSE AND HISTOPATHOLOGICAL ALTERATION IN VITAL ORGAN OF LABEO ROHITA (HAMILTON, 1822) CHALLENGE WITH PATHOGENIC AEROMONAS VERONII

Abstract

Aeromonas veronii is one of the principal bacterial pathogens of freshwater fishes. The present study examines immunological and histopathological alterations induced by A. veronii in Labeo rohita, the most important Indian major carp. The healthy Labeo rohita fingerlings were challenged with a pathogenic A. veronii suspension at concentrations of 10⁵ to 10⁹ CFU ml^-1. In the present study, the lethal dose (LD₅₀) of A. veronii for L. rohita is 2.5 × 107 CFU ml^-1. The clinical manifestations of diseased fish included hemorrhages, abnormal swimming, lethargy, and reduced feeding frequency during infection. The fish showed higher bacterial concentrations, with 86% and 100% mortality at 10⁸ and 10⁹ CFU ml^-1, respectively. Following post-infection with A. veronii, respiratory burst, bactericidal activity, and lysozyme activity increased significantly (p<0.05) after the post-infection. Moreover, the histopathological section of the gill exhibited curling of gill lamellae, infiltration of cells, fusion of secondary lamellae, and distorted gill lamellae. The liver section showed vacuolated necrosis of hepatocytes, loss of nuclei, and pyknosis. The kidney section showed loss of glomeruli, tubular distension, and melanomacrophage at some area. In conclusion, the lower bacterial load can be tolerated by L. rohita; however, higher concentrations can cause severe damage and alterations in L. rohita tissues, and may lead to mass mortality.