The participation of the Hypothalamic-Hypophysial Neurosecretory System (HHNS) in the initiation of anadromic fish migration was discovered. It is based on the results of ecological-histophysiological studies, using light microscopy, including immunohistochemistry, electron microscopy with quantitative morphometry. At the beginning of migration, an activation of neurosecretory products synthesis in pericarions of Nonapeptidergic Neurosecretory Cells (NSC) and their transport to neurohypophysis where they accumulate occurs. The excretion of neurosecretory products from pericarions of NSC into the liquor of the III brain ventricle is shown at the same time. We assume that HHNS causes a complex synchronous effect, which first consists of the active neurotropic action of Nonapeptide Neurohormones (NP-Nh) to the behavioral centers of the Central Nervous System (CNS), causing a dominant state of its excitation, designated as a migration impulse. In contrast, the cessation of viscerotropic action of NP-Nh through the general blood flow in neurohypophysis causes both the violation of the longly adapted level of the marine pastured type of osmoregulation, and the interruption of the known anti-gonadotropic action of NP-Nh. And the latter contributes to the transition of the body to the energy-intensive energetically type of metabolism. In subsequent navigation mechanisms, widely covered in world literature, the leading role is played by the gonadoliberinergic forebrain centers.
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