Structure of normal testis and testicular tumors in cyprinids from Lake Ontario.

Two types of testicular tumor were evident in cyprinid fishes collected from Lake Ontario. Both types of tumors appeared to be of Sertoli cell origin. One contained predominantly Sertoli cells with little or no lipid content and germinal cells in only small numbers. The second contained large numbers of spermatogonia together with Sertoli cells that contained large amounts of lipid and smooth endoplasmic reticulum. Small, apparently inactive Leydig cells were present in both types of tumors and also in testes of fish not bearing gonadal tumors.