TWENTY-SECOND ANNUAL EASTERN FISH HEALTH WORKSHOP ROYAL PAVILLION RESORT, ATLANTIC BEACH, NC MARCH 18 - 20, 1997 Pathogenesis of Experimental Edwardsiella tarda Infection in Channel Catfish (Ictalurus punctatus) Ahmad Darwish1, John A. Plumb2 and Joseph Newton2 1Department of Pathobiology, College of Veterinary Medicine, Auburn University, AL 36849; 2Department of Fisheries and Allied Aquacultures, Auburn University, Auburn, AL 36849 Infection trials of channel catfish with virulent Edwardsiella tarda were conducted by waterborne exposure of juvenile catfish to bacteria after scraping the skin. Fish became sluggish with rapid opercular movements. Dead fish had flared opercula with mouths agape and cutaneous ulcers and petechial hemorrhages were seen ventrally on the mouth, throat, operculum, abdomen, and lateral body. The site of scraping was swollen, inflamed, and progressed to focal ulcerative necrotizing dermatitis. Mucus production increased with random irregular, depigmented areas on the body. Internal organs were congested and livers had whitish discoloration and petechial hemorrhages. Clinical signs and internal gross lesions declined on d-8 and were not seen thereafter. Anterior and trunk kidney, and liver had necrotizing granulomatous inflammation. Red pulp of spleens was thin or destroyed while white pulp was hypocellular and contained predominantly macrophages. There was degeneration and necrosis of hemopoietic tissue and tubules of the trunk kidney. Multifocal hepatocellular necrosis accompanied by infiltration of macrophages occurred in the liver. Some macrophages contained large numbers of bacteria. Hepatic blood vessels were congested with large numbers of leukocytes. Bacteria in hepatic lesions stained with avidin-biotin conjugated imunoperoxidase technique using rabbit antibodies to E. tarda. Granulomatous lesions in the anterior kidney involved hemopoietic and interrenal tissue. No histological lesions were evident 6-d after infection. Colony forming units peaked on d-3 and bacteria were not cultured from tissues on d-8, 10, and 12. Lesions were not observed in intestine, stomach, heart, gill, or brain. Return to 22nd Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page