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Diseases of Aquatic Organisms

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DAO 40:147-155 (2000)  -  doi:10.3354/dao040147

Lympholeukemia in madai Pagrus major in Japan

Teruo Miyazaki1,*, Yukako Asai2, Tatsuya Kobayashi1, Masato Miyata1

1Faculty of Bioresources, Mie University, 1515 Kamihama, Tsu, Mie 514-8507, Japan
2Faculty of Medicine, Nagoya University, Tsurumai, Showa-ku, Nagoya, Aichi, Japan

ABSTRACT: Lympholeukemia has been occurring to an epizootic extent with mass mortality in 1 and 2 yr old madai (= Japanese red sea bream) Pagrus major in the winter season (October-May) in the western regions of Japan since 1975. Diseased fish displayed severe anemia and markedly increased numbers of neoplastic lymphocytoid and lymphoblastoid cells in the blood. Neoplastic cells originated in the splenic lymphatic cells and systemically caused severe metastatic lesions in the heart, liver, kidney, digestive tracts, gills and the lateral musculature. Electron microscopy revealed adeno-like viral particles (78 to 83 nm in diameter) in the nucleus of lymphoblastoid cells which appeared in the early prevalent stage but no viral particles in the lymphocytoid cells or plasmacytoid cells, which subsequently increased in number. In this paper, we describe light and electron microscopic features of neoplasms and neoplastic cells.

KEY WORDS: Lympholeukemia · Adeno-like virus · Red Sea bream

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