DAO 53:143-166 (2003)  -  doi:10.3354/dao053143

Myxosporean plasmodial infection associated with ulcerative lesions in young-of-the-year Atlantic menhaden in a tributary of the Chesapeake Bay, and possible links to Kudoa clupeidae

R. Reimschuessel1,*, C. M. Gieseker1,2, C. Driscoll2, A. Baya3, A. S. Kane4, V. S. Blazer5, J. J. Evans6, M. L. Kent7, J. D. W. Moran8, S. L. Poynton9,10

1US Food and Drug Administration, Center for Veterinary Medicine, Office of Research, Laurel, Maryland 20708, USA
2Maryland Dept of Natural Resources, Cooperative Oxford Laboratory, Oxford, Maryland 21654, USA
3Virginia-Maryland Regional College of Veterinary Medicine, University of Maryland, College Park, Maryland 20740, USA
4Aquatic Pathobiology Center, University of Maryland, Dept of Veterinary Medicine, College Park, Maryland 20742, USA
5US Geological Survey, National Fish Health Research Laboratory, Kearneysville, West Virginia 25430, USA
6US Dept of Agriculture, Agriculture Research Service, Aquatic Animal Health Research Lab, Chestertown, Maryland 21620, USA
7Center for Fish Disease Research, Dept of Microbiology, Oregon State University, Corvallis, Oregon 97331, USA
8School of Veterinary Medicine, University of California, 1 Shields Avenue, Davis, California 95616, USA
9Johns Hopkins University School of Medicine, Dept of Comparative Medicine, Baltimore, Maryland 21287, USA
10Institut für Gewässerökologie und Binnenfischerei, Müggelseedamm 310, Friederichshagen, 12587 Berlin, Germany
*Corresponding author. Email:

ABSTRACT: Ulcers in Atlantic menhaden Brevoortia tyrannus (Latrobe) (Clupeidae), observed along the USA east coast, have been attributed to diverse etiologies including bacterial, fungal and, recently, harmful algal blooms. To understand the early pathogenesis of these lesions, we examined juvenile Atlantic menhaden collected during their seasonal presence in Chesapeake Bay tributaries from April to October 1999 and from March to August 2000. We conducted histopathological examinations of young-of-the-year fish from the Pocomoke River tributary, which has a history of fish mortalities and high lesion prevalence. Kudoa clupeidae (Myxozoa: Myxosporea) spores were present in the muscles of fish collected in both years. Of the fish assessed by histology in April, 5 to 14% were infected, while in May 90 to 96% were infected. Infection rates remained high during the summer. Mature spores were primarily located within myomeres and caused little or no observable pathological changes. Ultrastructure showed spores with capsulogenic cells bearing filamentous projections, and a basal crescentic nucleus with mottled nucleoplasm containing cleaved, condensed chromatin. Also, a highly invasive plasmodial stage of a myxozoan was found in the lesions of juvenile Atlantic menhaden. The plasmodia were observed in fish collected between May and July, with the maximum occurrence in late June 1999 and late May 2000. Plasmodia penetrated and surrounded muscle bundles, causing grossly observable raised lesions in 73% of all fish infected with this invasive stage. Plasmodia were also detected in the visceral organs, branchial arches, and interocular muscles of some fish. Some of the invasive extrasporogonic plasmodial lesions were associated with ulcers and chronic inflammatory infiltrates. The plasmodial stage appeared to slough out of the tissue with subsequent evidence of wound healing. Ultrastructure showed plasmodia with an elaborate irregular surface, divided into distinct ectoplasm and endoplasm; the latter contained numerous spherical vegetative nuclei, secondary generative cells, and occasional cell doublets. Our ultrastructural studies indicate that the plasmodial organisms, which are important in the etiology of the skin lesions, are myxozoans, and they may represent early stages of K. clupeidae.

KEY WORDS: Atlantic menhaden · Brevoortia tyrannus · Kudoa clupeidae · Myxosporea · Plasmodia · Lesions

Full text in pdf format