Photobacterium damselae subsp. damselae associated with bacterial myonecrosis and hepatopancreatic necrosis in broodstock Pacific white leg shrimp, Litopenaeus vannamei (Boone, 1931)

Abstract

This study presents the first report of myonecrosis and hepatopancreatic necrosis in broodstock of Litopenaeus vannamei. Of the 400 individuals examined, 34 displayed myonecrosis and hepatopancreatic necrosis, conditions previously reported to be caused by bacterial, fungal, parasite, and viral infections. Gross signs of infection include passive swimming, anorexic and the abdominal muscle become opaque with extensive whitish discoloration of distal abdominal segments and the posterior appendages. Macroscopic necropsy examination revealed atrophied hepatopancreas and empty stomach and mid-gut. The histopathological investigations revealed that reddened muscular lesions are composed of coagulative and liquefactive necrosis of striated muscle fibers, often with edema. The hepatopancreas showed necrotic lesions displaying disorganized lumen and dispersed tubular epithelial cells scattered on necrotic myoepithelial cells. Gill lamellae in infected shrimp showed disorganized, necrotic filaments infiltrated with inflammatory hemocyte. The RT-PCR analysis using OIE-recommended primer and additional sets of primers used in previous studies revealed the absence of IMNV as well as other emerging pathogens including MrNV, PvNV, WSSV, IHHNV, TSV, YHV, AHPND, and EHP. Basis on these negative results, microbiological tests were performed. A dominant yellow-colored bacterial colony was isolated on TCBS agar and identified as Photobacterium damselae subsp. damselae KPD. Injection of the isolate of P. damselae KPD proved to be pathogenic to L. vannamei. The study concludes that P. damselae KPD is the causative agent of myonecrosis and hepatopancreatic necrosis and represents a threat to the Indian shrimp hatcheries.