TWENTY-FIFTH ANNUAL EASTERN FISH HEALTH WORKSHOP MARCH 10-13, 2000     Massive Hepatic Necrosis And Nodular Regeneration In Largemouth Bass Fed Feeds High In Available Carbohydrate       Andrew E. Goodwin1,   Darlene M.Tieman1, Rebecca T. Lochmann1, and Andrew J. Mitchell2     1University of Arkansas at Pine Bluff, Aquaculture/Fisheries Center, 1200 N. University Dr., PO Box 4912, Pine Bluff, AR  71611; 2U.S. Department of Agriculture, Agricultural Research Service, Harry K. Dupree Stuttgart National Aquaculture Research Center, PO Box 860, Stuttgart, AR  72160       There is a niche market for live 0.5 kg largemouth bass, Micropterus salmoides, in Asian fish markets on the east and west coasts of the United States.  Largemouth bass are piscivores and  very reticent to eat prepared feeds but can be trained to do so with diligent effort. In the winter of 1998, the largest producer of bass on feed suffered a significant increase in shipping-related and in-pond mortality.  No bacterial, viral, or parasitic pathogens were found at necropsy.  Livers of affected 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, islands 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 (RTLA #6731-6738).  Sequential studies of bass in ponds revealed that bass progressively accumulated glycogen in their hepatocytes to an extent sufficient to explain the massive necrosis of that organ.  Aquarium trials were begun using feeds with varying amounts of available carbohydrate and lipid.  An experimental floating diet designed to contain 45% protein, 25% fat, and 8% available carbohydrate produced significantly less hepatic glycogen accumulation, lower hepatosomatic indexes, and increased hepatic and whole-body lipid when compared to the old diet containing 46% protein, 16% fat, and 15% available carbohydrate. The farmer switched to the 45 % protein, 25% fat feed in the summer of 1999. One-year-old fish examined in February, 2000 had no hepatic nodules or necrosis and no losses occurred in ponds or during shipping through March 1, 2000.     Return to 25th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page