Lymphoma in the Japanese medaka Oryzias latipes

Abstract

Six adult Japanese medaka Oryzias latipes were diagnosed with lymphoma, over a 6 mo period, frorn a control population of broodstock fish. Tumors were equally split among males and females, and presented as e~ther grossly visible cranial masses, unilateral exophthalmos, or with n o gross lesions. Tumors were classified as renal, thymic, or chssemmated based on histologic distribution and the extent of neoplast~c infiltrate. Metastatic lesions were found in all 6 fish and occurred via both direct extension and vascular invasion. The etiology of the tumors has not been determined.