TWENTY-THIRD ANNUAL EASTERN FISH HEALTH WORKSHOP JOHN CARVER INN, PLYMOUTH, MA 30 MARCH - 2 APRIL, 1998 Characterization Of Lesions On Atlantic Menhaden From The Pocomoke River Christine Densmore and Vicki Blazer National Fish Health Research Laboratory, USGS/BRD1700 Leetown Road, Kearneysville, WV In August 1997, two fish kills involving menhaden were reported in the waters of the lower Pocomoke in the vicinity of Shelltown. Subsequently, these two fish kills have been associated with blooms of toxic dinoflagellate(s) (Pfiesteria piscicida or Pfiesteria-like organisms). Juvenile Atlantic menhaden (Brevoortia tyrannus) were the primary species involved in each of the fish kills. According to surveys conducted by the Maryland Department of Natural Resources, approximately 90% of menhaden sampled from trawl nets along the affected stretch of the river during and following the fish kills had gross lesions. These lesions were varied, but predominantly appeared as circumscribed areas of hyperemia, dermal erosion, and tissue slough-ing over the epaxial, abdominal, perianal, or caudal regions. Lesions often appeared to penetrate deeply into the underlying musculature with necrotic tissue debris protruding from the wound. These lesions showed evidence of necrotizing dermatitis and myositis with floccular degeneration of skeletal muscle. Severe chronic granulomatous inflammation with hemorrhage, extensive tissue infiltration by lymphocytes and mono-nuclear cells, and multinuclear giant cell formation were also apparent. Where the lesion had penetrated to the abdominal cavity, abdominal organs were often involved; otherwise, involvement of other organ systems was limited. Aseptate fungal hyphae were evident throughout the lesions, particularly in association with granuloma formation. These lesions, both grossly and histologically are remarkably similar to lesions found in the disease syndromes epizootic ulcerative syndrome, red spot disease, mycotic granulomatosis, and ulcerative mycosis affecting fish species, including Atlantic menhaden, throughout the Asia-Pacific area, Australia, and the mid-Atlantic United States. Although lesions from the Pocomoke menhaden are thought to be associated with acute epizootics involving the toxic Pfiesteria complex, the chronic nature of the lesions described implies no direct relationship with ongoing blooms of toxic dinoflagellates.   Return to 23rd Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page