Submitted to: European Association of Fish Pathologists
Publication Type: Proceedings
Publication Acceptance Date: 5/12/1999
Publication Date: N/A
Citation: Goodwin, A.E., Mitchell, A.J. Idiopathic hepatic necrosis in largemouth bass (micropterus salmoides)cultured with domestic ducks. European Association of Fish Pathologists. 1999. p.1. Interpretive Summary:
Technical Abstract: The largemouth bass, Micropterus salmoides, is the most important freshwater gamefish in the southern United States. The aquaculture industry provides fingerlings for stocking, and also produces small numbers of larger bass that have been trained as fry to eat pelleted feeds. On one farm in Arkansas, USA, a producer of large bass on feed suffered a significant increase in shipping-related mortality. No bacterial, viral, or parasitic pathogens were found at necropsy. Livers of effected fish were pale and translucent with large 3-10 mm yellow to pink nodules on their surface and in the parenchyma. Histological examination of these livers showed that the translucent regions of the liver contained few hepatocytes and were primarily composed of connective tissue and cell types consistent with chronic inflammation. Also noted were numerous eosinophils, island of pancreatic and billiary cells, and small granulomas that did not stain positively for mycobacteria. The nodules appeared to be areas of multifocal regeneration of normal hepatocytes rather than hepatocellular neoplasms. Apoptotic hepatocytes were common in the nodules. The histologic appearance of the livers was similar to that of salmonids exposed to aflatoxins, however, bass and salmonids on other farms, eating the same type of feed from the same manufacturer, had no liver lesions. A survey of ponds on the effected farm revealed a perfect correlation between the liver damage and the presence, in the pond, of domestic ducks fed on rice. Direct consumption, by bass, of rice that may have been contaminated with aflatoxin is very unlikely due to the dietary preferences of these fish.