Abstract A poorly differentiated subcutaneous neoplasm occurred in a white bass Morone chrysops collected from a freshwater lake in Oklahoma. The neoplasm was a solitary soft round mass that bulged from the anal fin. Histologically, the neoplasm was lobular and consisted of islands of spindle-to- stellate cells separated by clefts. The islands frequently contained capillary profiles and deposits of an amorphous eosinophilic material. The lesion was mesenchymal and suggestive of a poorly differentiated hemangiopericytoma, though it might have derived from nerve sheath, pigment cells, fibroblasts, or smooth muscle. An epizootic of another type of dermal neoplasm, a poorly differentiated spindle cell tumor, has been reported in gizzard shad Dorosoma cepedianum residing in the same lake. However, etiology of the neoplasms from both the white bass and the shad remains uncertain.