THE REPRODUCTIVE BRAIN IN FISH

In fish as in other vertebrates, the brain is actively involved in the control of reproduction, first by participating, under the influence of external factors, in the establishment of an appropriate endocrine status, but also by allowing synchronization of the partners by the ti me of spawning. It is now well established that the pituitary gonadotr opic function is controlled by multiple stimulatory and inhibitory fac tors, originating mainly from the preoptic region and the mediobasal h ypothalamus, both target regions for sexual steroids. Little is known about the mechanisms involved in the mediation of external and interna l factors, however there is indication that internal factors, such as androgens and melatonin, known to trigger particular behavioural and e ndocrine responses, act both at the level of neuroendocrine territorie s, but also on sensorial systems, which are the actual sites of action for external factors. This paper represents an attempt to summarize a nd integrate the recent literature devoted to the different aspects of the brain as a major participant in the complex endocrine and behavio ural mechanisms of reproduction in fish.