TWENTY-FOURTH ANNUAL EASTERN FISH HEALTH WORKSHOP Royal Pavilion Resort, Atlantic Beach, NC MARCH 9-11, 1999 Case History: Gill Pathologies Associated With Acute And Chronic Mortalities In Arctic Charr (Salvelinus alpinus) Cultured In A Semi-Closed Recycle System Alicia C. Noble1, Jeffrey C. Wolf2, Graham L. Bullock1, Stephen A. Smith2, Scott Tsukuda1, and Julie Bebak1 1Freshwater Institute, P.O. Box 1889, Shepherdstown, WV 25443; 2Department of Biomedical Sciences and Pathobiology, VA-MD Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 A cohort of 2520 arctic charr (Salvelinus alpinus) with an average size of 270 gms, was introduced into a semi-closed recycle system at a density of 71.6 kg/m3. About two months after introduction, fish stopped gaining weight and feed consumption decreased, followed several days later by no feeding response. Mortalities of a few fish per day occurred for about a week, then increased, peaked at about 225 fish per day and then decreased. Macroscopically, gill filaments had inflamed tips and white patches. Excess mucus and hyperplasia of the gills was observed on wet mounts. All cultures for systemic bacteria, FA tests, and wet mount observations were negative for pathogens. Assays for IPNV, IHNV, VHSV, and ISAV were also negative. Feed samples were negative for rancidity and mycotoxins. Histopathology samples revealed severe chronic-active gill inflammation that was most likely responsible for the high mortalities. All fish in the sample taken during acute mortalities showed a severe chronic diffuse granulocytic and suppurative proliferative branchitis with secondary lamellar fusion and mucus cell hyperplasia. Numerous eosinophilic intranuclear inclusions within primary lamellar epithelial cells were commonly associated with the hyperplasia and inflammation in severely affected fish. These inclusions did not stain as DNA with a Feulgen’s stain, and did not appear to resemble viral particles ultrastructurally. In one of the sample groups gill tissue contained irregular granular basophilic intracytoplasmic inclusions within scattered epithelial cells of secondary lamellae. These PAS-negative inclusions stained intensely acidopilic with Gram’s stain but did not appear to be bacteria. The same inclusions were red when a Machiavello’s stain was utilized, however their morphology and tinctorial properties were not identical to the epitheliocystis inclusions that have been observed in the gills of tilapia. Electron microscopy of the epithelial cells of the gill showed a large, single, centrally-located aggregate of amorphous electron-dense granular material most consistent with nucleolar hypertrophy. Immunohistochemistry performed on gill samples using anti-chlamydial antibodies was negative. Return to 24th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page