TWENTY-FOURTH ANNUAL EASTERN FISH HEALTH WORKSHOP Royal Pavilion Resort, Atlantic Beach, NC MARCH 9-11, 1999 First Report Of Swim Bladder Fibrosarcoma In Atlantic Salmon In The United States And An Associated Retrovirus Paul R.Bowser1, J.W.Casey1, S.L.Quackenbush1, R.N.Casey1, J.A.Coll2, and L. Lofton3 1Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853-6401; 2Northeast Fisheries Center, U.S. Fish and Wildlife Service, Lamar, PA 16848; 3U.S.Fish and Wildlife Service, North Attleboro, MA 02760. A population of adult Atlantic salmon (Salmo salar) held at the North Attleboro National Fish Hatchery (NANFH) were experiencing chronic mortalities. The fish were captured from the Pleasant River, ME and held at the hatchery for use as brood fish. Progeny from these fish were to be used to augment the Atlantic salmon population of the Pleasant River, one of six rivers designated for this program. Moribund Atlantic salmon exhibited external signs that included swollen abdomen, as well as multifocal hemorrhage on the body and fins. Some fish also exhibited circular to irregularly shaped white areas on the skin. On close examination, these areas appeared to be sites where there was a sloughing of the epidermis. The hemorrhagic lesions and white areas on the skin are thought to be indicative of the early stages of infection, although their true relationship to the disease process has not been confirmed. Affected fish may also exhibit signs of lethargy and poor growth. Upon necropsy, some fish had multinodular masses of the swim bladder. In advanced cases, these multinodular masses replaced the entire swim bladder. Upon dissection of the tumor from affected fish, the neoplasm appeared to develop from both the external and internal surfaces of the swim bladder. In advanced cases, the size of tumors may be so great that other internal organs are displaced, resulting in a distended abdomen. Upon histological examination, the tumors were observed to be made up of well-differentiated fibroblastic cells that are arranged in interlacing bundles. A similar outbreak of swim bladder fibrosarcoma occurred in cage-cultured Atlantic salmon in Scotland in 1976. Electron microscopy revealed the presence of retrovirus-like budding from swim bladder sarcoma cells. In this case, we identified the presence of a retrovirus through the use of degenerate RT-PCR and gene sequencing techniques. The specific role of this retrovirus in the development of Atlantic Salmon Swim Bladder Sarcoma is under investigation. Return to 24th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page