Neuronal embryonal tumors in fish

This article describes 11 cases of neuronal embryonal neoplasia in captive adult teleost fish. Neoplasms were located within 1 or both eyes of 8 fish and the skin of 3 other fish. Ocular neoplasms most often presented as unilateral or bilateral exophthalmia. Seven ocular and 1 cutaneous mass were composed of small triangular (carrot-shaped) neoplastic cells with Flexner-Wintersteiner-type rosette formation. Mass location and histologic and ultrastructural features were suggestive of retinoblastomas. One ocular mass was composed of ribbons and rosettes of neoplastic cells with multiple areas of neuronal differentiation and was diagnosed as a teratoid medulloepithelioma. A cutaneous mass from an electric eel (Electrophorus electricus) consisted of rosettes and streams of elongate neoplastic cells. The epidermal electroreceptor (ampullary) organ was considered as an origin. Although distant metastases were not observed, neoplasms were generally locally aggressive with postexcision recurrence. There was occasional spread to or de novo occurrence within the contralateral eye.