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Monitoring Results Of Lesions In
Young Menhaden, Brevoortia tyrannus (Latrobe), In Chesapeake Bay: 1999
And 2000 R. Reimschuessel1, C. Gieseker2,
A. Baya3, S. Poynton4, A. S. Kane5, V Blazer6,
J. J. Evans7, M. Kent8,
J. D. W. Moran9, C. Driscoll2 1U.S.
Food and Drug Administration, Center for Veterinary Medicine, Office of
Research, Laurel, MD 20708; 2Maryland
Department of Natural Resources, Cooperative Oxford Laboratory, Oxford, MD 21654; 3Virginia-Maryland
Regional College of Veterinary Medicine, University of Maryland, College Park,
MD 20740; 4Division of
Comparative Medicine, Johns Hopkins University School of Medicine, Baltimore,
MD. 21205-2196; 5University of Maryland School of Medicine, Aquatic
Pathobiology Center, Department of Pathology, Baltimore, MD 21201; 6U.S. Geological Survey,
Kearneysville, West Virginia, 25430; 7U.S.
Department of Agriculture, Agriculture Research Service, Aquatic Animal Health
Research Laboratory, Chestertown, MD 21620; 8Department of
Microbiology Oregon State University, Corvallis, Oregon 97331; 9School
of Veterinary Medicine, University of California, Davis, CA 95616. As part of the Maryland Department of Natural Resources’ routine monitoring program, Atlantic menhaden (Brevoortia tyrannus) were collected during their seasonal presence in Chesapeake Bay tributaries to monitor for external lesions. In 1999, May-June, 0.39% of menhaden collected had external lesions and July-September, 0.49% of menhaden collected had lesions. In 2000, May-June, 0.05% of menhaden had external lesions and July-September, 4.56% of menhaden had lesions. Routine histopathological examinations were conducted of fish from the Pocomoke River, due to its history of fish kills and high lesion prevalence, as well as periodic comparisons to other tributaries. In late May 1999, 90% of Pocomoke R. juvenile menhaden had mature Kudoa sp. spores infecting their muscles, in contrast to 40% and 30% in the Transquaking and Nanticoke Rivers. In addition to the Kudoa sp. spores, a highly invasive, plasmodial stage suggestive of a myxozoan was found in the tissues of the Pocomoke R. menhaden during late April through early July, 1999-2000. In both years, invasive plasmodia were present in juvenile menhaden for approximately 6 weeks (late May to early July, 1999; late April to early June, 2000). During this period, approximately 50% of the menhaden sampled for histology had plasmodial lesions in either muscles or viscera. Of the menhaden infected by the plasmodia, 63% had grossly observable lesions associated with the plasmodia. Here we present the epidemiological data from the 1999 and 2000 sampling seasons in comparison to some relevant environmental data. |