Trends of Hormonal Levels in the Brain, Pituitary and Serum of Chum Salmon during Homing Migration

摘要

In salmonids, at a particular stage of ocean growth, certain endocrinological changes cause the fish to shift from feeding migration to spawning migration. Previous reports indicate that this shift has been thought to coincide with the onset of gonadal maturation which in turn is regulated by brain-pituitary-gonadal axis (Urano et al. 1999). The hypothalamic decapeptide, gonadotropin-releasing hormone (GnRH) is secreted from axon terminals of GnRH neurons and carried to pituitary where it stimulates the release of gonadotropins (GTHs) from gonadotrophs into the blood stream (King and Millar 1992). GTHs control gametogenesis and production of gonadal steroid hormones (Nagahama 1994).