Testicular development and plasma sex steroid levels in cultured male Senegalese sole Solea senegalensis Kaup

Testicular development and plasma levels of sex steroids (11-ketotestosterone (11-KT), testosterone (T) and 17,20 -dihydroxy-4-pregnen-3-one (17,20 -P)) were investigated for the Wrst time in cultured male Senegalese sole Solea senegalensis. The germ cell dynamics and gonadosomatic index (IG) were monitored. Based on the relative abundance of the diVerent types of germ cells present, the spermatogenetic cycle was divided into Wve stages: early (I; spermatogonia (SPG)), mid (II; SPG, spermatocytes (SPC) and spermatids (SPD)), and late spermatogenesis (III; SPC, SPD, and spermatozoa (SPZ)), functional maturation (IV; SPD and SPZ), and recovery (V; SPD, SPZ, and SPG). During summer, Wsh had stage I and V testes and the lowest values in plasma levels of sex steroids and IG. Testicular recrudescence seemed to begin in autumn, as denoted by the Wrst increase in IG and in the levels of 11-KT and T, and the appearance of testes at stage II and III. During winter, the levels of 11-KT and T peaked and soon began to decrease, the IG slightly declined and the proportion of running males (RM) gradually increased. In spring, levels of 11-KT and T continued to decline, the IG slightly increased and the proportion of RM peaked concomitantly with the occurrence of stage IV testes. Plasma levels of 17,20 -P did not change signiWcantly throughout testicular development. Transformation of SPD into SPZ followed a group-synchronous fashion, a phenomenon which parallels asynchronous oocyte development reported in females. This mechanism would be consistent with the observed small quantity of sperm that can be manually stripped at any one time and other aspects of S. senegalensis reproductive biology