Incidence of multiple bacterial infections in Pacific whiteleg shrimp, Litopenaeus vannamei

Abstract

A rare incidence of multiple bacterial infections was reported in Litopenaeus vannamei grow-out ponds in India. The pathogenic organisms identified are Aeromonas veronii, Bacillus flexus, Kurthia gibsonii, Shewanella decolorationis, Bacillus cereus and Shewanella amazonensis. The infected shrimp showed various clinical and morphological changes such as mucus secretion in the hepatopancreas, bacterial spots in the carapace, red or pink discoloration of abdomen with black stripes and highly melanized body. The Histological studies of the hepatopancreas revealed bacterial plaque in the lumen, inflammatory response, necrosis of connective tissue and lipid droplets. The histology of stomach detected degradation of spongy connective tissue, hypertrophied nucleus and the abdomen showed bacterial plaques in the gaps of the muscle fibre. Histochemically, both gram-positive and gram-negative bacteria's were identified in the hepatopancreas and the presence of mucus in the lumen of hepatopancreatic microtubules was confirmed by Alcian blue staining. The electron microscopic studies of the infected shrimp showed multiple bacterial infections and cellular responses like phagocytosis in the hepatopancreas, using transmission electron microscope and scanning electron microscopic confirmed the presence of bacillus and coccobacillus-shaped bacteria in carapace.