The African catfish, Clarias gariepinus, a model for the study of reproductive endocrinology in teleosts

In their natural habitat African catfish, Clarias gariepinus, show a discontinuous reproductive cycle. This cycle follows changes in the gonadotropic activity of the pituitary. Gonadotropin release has been shown to be under dual hypothalamic control, i.e. a gonadotropin-releasing hormone (GnRH) and a gonadotropin release-inhibiting factro (GRIF), which turned out to be dopamine. Gonadal sex hormones influence gonadotropin release by a negative feedback, and a model has been developed to explain their mode of action. Steroid formation has been studied in testes, seminal vesicles and ovaries and correlated with the annual reproductive cycle. Steroid glucuronides, originating from the seminal vesicle, act as male sex pheromones; ovulation seems to be synchronized by female pheromones. Techniques for the induction of ovulation were developed. Only broodfish, reared from eggs to maturity under favourable conditions, show a continuous reproductive cycle and can be induced to produce viable eggs throughout the year