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

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 · LesionsResale or republication not permitted without written consent of the publisher

Molecular Assays for DetectingAphanomyces invadansin Ulcerative Mycotic Fish Lesions

“…A. invadans, however, should not be considered the sole etiology for ulcerative lesions. Stress, poor nutrition, and certain parasite, bacterial, and viral infections are all capable of producing similar lesions (20,24,32,39). …”

Myxozoan genera: definition and notes on taxonomy, life-cycle terminology and pathogenic species

“…In young C. harengus, heavy infections may induce mortalities. Lesions in Brevoortia tyrannus were studied by Reimschuessel et al (2003).…”

Etiology of ulcerative lesions of Atlantic menhaden (Brevoortia tyrannus) from James River, Virginia

“…Thirty-eight representative B. tyrannus were transferred to the laboratory for further analysis; including unremarkable fish with no lesions or external anomalies (n=3), those with pre-ulcerative boil-like lesions (n=3), and those with severe, focal ulcers (n=32). The gross appearance of severe focal ulcers was similar to lesions previously described for B. tyrannus and attributed either to Myxosporea (Reimschuessel et al 2003), fungi similar to Aphanomyces invadens (Blazer et al 1999), or the dinoflagellate P. piscicida (Burkholder et al 2001). In this epizootic event, many B. tyrannus had pre-ulcerative areas (morphology not described in previous episodes) characterized by raised or swollen dermis with a boil-like appearance (Fig.…”