histological characteristics and gametogenesis have received little attention in endemic mexican fish, thus they are little understood. in this study, the histology of the testis of charal chirostoma jordani, and ultrastructure of gamete cells through fotonic and electron microscopy are described. sixty male fish were collected in corrales, hidalgo state, méxico, 70 km nw méxico city. charal testis are paired, and added to the dorsolateral wall of abdomen. they are covered by a mesorquium, which has small black pigmentation spots. testes are tubular, and spermatogonia are restricted to the distal part of tubules, basically in the cortical region. cell sizes were measured: spermatogonia (8 + 0.7 μm), primary spermatocytes (6.2 + 0.3 μm), secondary spermatocytes (4.4 + 0.1 μm), spermatids (2.5 + 0.2 μm) and spermatozoa (15.4 + 0.3 μm). sertoli cells surround gamete cells; together they form cysts which have approximately the same degree of development. all the testes have gamete cells simultaneously, and leydig cells are easy to see in the central part of the testis.
