Gonadal steroid hormones drive puberty in fish

Development to sexual maturity reflects an activation of all levels of the brain-pituitary-gonad (BPG) axis. It is hypothesized that sex steroids are involved in this activation. We used the male African catfish, Clarias gariepinus, to challenge this hypothesis. Steroid hormone synthesis during pubertal development was analyzed and 11 beta-hydroxyandrostenedione (OHA) was identified as the main product of the testis. However, OHA is then converted by the liver to 11-ketotestosterone (KT), the main androgen in the circulation. The significance of OHA, KT and other steroid hormones for testicular development (in terms of androgen production and gametogenesis), pituitary development (morphology, gonadotropin (GTH) gene expression and gonadotropin-releasing hormone (GnRH) responsiveness), and finally GnRH neurone development will be discussed.