Histopathology of Gill, Liver, and Pancreas, and Serum Enzyme Levels of Channel Catfish Infected withAeromonas hydrophilaComplex

Abstract

Channel catfish Ictalurus punctatus infected with Aeromonas hydrophila complex were examined 2–21 d after they were moved from earthen ponds to tanks. These infections by A. hydrophila complex were categorized into three groups: (1) motile aeromonad septicemia (MAS; systemic infection and signs of disease), (2) cutaneous (infection limited to skin and the underlying muscle), and (3) latent (systemic infection but no external signs of disease). Hepatic necrosis was associated with all types of infections but was most consistently present and sometimes more severe in fish with MAS. Hepatic steatosis was also associated with MAS. Systemically infected fish, including fish with latent infections, tended to have pancreatic atrophy and necrosis. There was a lack of infiltrating leukocytes in necrotic areas of the liver and intrahepatic exocrine pancreas of infected fish, and there was no consistent relationship between infection by A. hydrophila complex and hepatic hemorrhage or hemosiderosis. Spongiosis of gill epithelium was present in fish with any of the three infection types, but fish with MAS had a more severe branchitis, as indicated by leukocytic infiltration and dilation of the central venous sinus. Fish with MAS or latent infections had enlarged nuclei in the branchial epithelium. There was a significant relationship between these gill lesions and the occurrence or severity of hepatic and pancreatic lesions. The mean activities of aspartate aminotransferase and lactate dehydrogenase were significantly increased in fish with MAS but not in fish with one of the other types of infections.