Testosterone Inhibits 11-Ketotestosterone-Induced Spermatogenesis in African Catfish (Clarias gariepinus)1

Male fish produce 11-ketotestosterone as a potent androgen in addition to testosterone. Previous experiments with juvenile African catfish (Clarias gariepinus) showed that 11-ketotestos-terone, but not testosterone, stimulated spermatogenesis, whereas testosterone, but not 11-ketotestosterone, accelerated pituitary gonadotroph development. Here, we investigated the effects of combined treatment with these two types of andro-gens on pituitary gonadotroph and testis development. Imma-ture fish were implanted for 2 wk with silastic pellets containing 11-ketotestosterone, testosterone, 5a-dihydrotestosterone, or estradiol-17b; cotreatment groups received 11-ketotestosterone in combination with one of the other steroids. Testicular weight and pituitary LH content were higher (two- and fivefold, re-spectively) in the end control than in the start control group, reflecting the beginning of normal pubertal development. Treat-ment with testosterone or estradiol-17b further increased the pituitary LH content four- to sixfold above the end control lev-els. This stimulatory effect on the pituitary LH content was not modulated by cotreatment with 11-ketotestosterone. However, the stimulatory effect of 11-ketotestosterone on testis growth and spermatogenesis was abolished by cotreatment with testos-terone, but not by cotreatment with estradiol-17b or 5a-dihy-drotestosterone. Also, normal pubertal testis development was inhibited by prolonged (4 wk) treatment with testosterone. The inhibitory effect of testosterone may involve feedback effects on pituitary FSH and/or on FSH receptors in the testis. It appears that the balanced production of two types of androgens, and the control of their biological activities, are critical to the regulation of pubertal development in male African catfish. luteinizing hormone, pituitary, puberty, spermatogenesis, steroid hormones, testi