Histopathological and ultrastructural studies on melanomas in xiphophorus fish

One thousand five hundred swordtail fishes (xiphophorus) were examined to r ecord the mast common neoplasms in this fish. Fifty seven fish (3.8 %) show ed spontaneous melanomas. Melanomas were experimentally induced using gamma and UV rays. Spontaneous or experimentally induced melanomas were studied histopathologically and ultrastructurally. The spontaneous melanoma reveale d the occurrence of the melanoma in the form of sequenced lesions. Melanoma s appeared in experimentally irradiated fishes 2 - 3 months from first expo sure. The tumour appeared initially as black spots and changed to a large m elanotic swelling.