ABSTRACT
Reproduction in fishes is, as in other vertebrates, under neuroendocrine control but the functions of hypothalamus, pituitary and gonads are particularly influenced by environmental factors. Gonadotropin-Releasing Hormone (GnRH) represents the first step in a cascade of events coordinating the complex physiology of reproduction and reproductive behavior in vertebrates. The natural GnRH forms play pivotal roles in the regulation of vertebrate reproduction and exert other physiological functions through binding to their specific membrane receptors (GnRHRs). Steroid hormones and their receptors are of central importance in the endocrine control of physiological functions critical for the survival and propagation of the species, such as reproduction, behavior, salt balance, metabolism, immune function and resistance to stress. The numbers and size of GnRH neurons are modified by changes in the social environment influencing the reproduction status and sex in adults. In aquaculture, a sound knowledge of the mechanisms and external factors controlling reproduction is also important.
