Hemorrhage Disease of Cultured Tra Catfish (Pangasianodon hypophthalmus) in Mekong Delta (Vietnam)

Abstract

This study investigated hemorrhage disease in cultured tra catfish (Pangasianodon hypophthalmus) from An Giang, Ben Tre, Can Tho, and Vinh Long provinces in the Mekong Delta (Vietnam). The disease is characterized by internal organ necrosis, white (spot) nodules in the liver, kidney, and spleen, and petecchial hemorrhages on the tail, fins, and abdomen. Some fish have exophthalmus (pop eye), a reddish and swollen anus, and yellowish fluid in the peritoneal cavity. Moribund fish lose their appetite and swim at the sur- face. Bacteria isolated from the diseased fish consisted of Aeromonas hydrophila (38.8%), A. sobria (4.1%), A. caviae (2.0%), Edwardsiella ictaluri (4.1%), and a gram positive, anaerobic bacteria, Clostridium sp. (40.8%). Histological analyses showed necrotic cells and intranuclear, randomly- arranged, straight rod cells (1.0-1.5 x 3.0-4.0 μm) concentrated in the ulcers. Challenge test with A. hydrophila induced external signs of hemorrhagic dis- ease. Challenge test with Clostridium sp. confirmed the presence of the bac- teria in infected tissues with development of white nodules similar to those in naturally-infected fish. Fish challenged with E. ictaluri exhibited gas bubbles in the stomach and gut with a foul smell. Reovirus-like particles were seen by transmission electron microscopy. Further study is needed to determine the role of each pathogen alone and together with others in the pathogenesis of hemorrhage disease of tra catfish.