Reproduction of fish, as in other vertebrates, is controlled by the brain through the endocrine system. The pituitary gland plays a major role in initiating reproductive maturation (puberty), maintaining production of sperm and eggs by the gonads, and inducing final maturation and gamete release (spawning). In tetrapod vertebrates, two pituitary hormones regulate reproduction; follicle-stimulating hormone (FSH), which stimulates early stages of gametogenesis, and luteinizing hormone, which induces ovulation and corpus luteum formation in the female, for example. Until recently, it was generally believed that the pituitary gland of fish produced only one hormone that controlled all aspects of reproduction. It is now established that in salmon there are two pituitary hormones, gonadotropin I and gonadotropin II, that may control reproduction. The proposed research will study the functions of these two gonadotropins in salmon. The study will also address when the two gonadotropins first appear in the pituitary gland and blood, and how the brain controls their synthesis and release. This work is significant in that it should advance our knowledge of how salmon reproduction is controlled. Since it is well-established that reproduction in tetrapod vertebrates is controlled by two pituitary hormones, comparison of fish can be made with mammals, birds, amphibians and reptiles. This information should give us a better perspective on vertebrate reproduction in general. Futhermore, a better understanding of the control of fish reproduction will allow the rational development of techniques to manage reproduction of captive broodstock in fish aquaculture.
