A complete study of neuroendocrine regulation of fish reproduction. 4. Migration impulse as a starting mechanism of spawning
Authors:   St. Petersburg State Agrarian University, Pushkin, St. Petersburg, Russia, Garlov P.E. , Rybalova N.B. ,   St. Petersburg State Agrarian University, Pushkin, St. Petersburg, Russia, Nechaeva T. A. ,   St. Petersburg State Agrarian University, Pushkin, St. Petersburg, Russia, Temirova S.A. ,   St. Petersburg State Agrarian University, Pushkin, St. Petersburg, Russia, Denisenko A.N. ,   St. Petersburg State Agrarian University, Pushkin, St. Petersburg, Russia, Kuzik V.V. ,   Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences, St. Petersburg, Russia
Published: September 2024

The participation of the hypothalamo-hypophysial neurosecretory system (NS) in the initiation of anadromous fish spawning migration was established on the basis of ecological-histophysiological analysis the results of histomorphological, immunohistochemical and electron microscopic studies for the first time. Activation of the neurosecretory products synthesis in the neurosecretory cells perikaryons and their excretion into the cerebrospinal fluid of the III brain ventricle in anadromous migrants forms at the beginning of the river spawning migration, spring-spawning: Russian sturgeon, stellate sturgeon and autumn-spawning: pink salmon and chum salmon, was shown. Transport and mass accumulation of neurosecretory products in the neurohypophysis were discovered at the same time. It is concluded, that the NS impacts a complex synchronous effect, which consists: firstly, in the neurotropic effect of nonapeptide neurohormones (NPh) on behavioral centers, which causes a dominant state of CNS excitation corresponding to the “Migration impulse”; secondly, in the violation of the long-term adapted marine “Pastured” level of osmoregulation; and thirdly, in the cessation of the well-known antigonadotropic effect of NPh, which contributes the organism transition to the energyconsuming energy type of metabolism. A comparative analysis (cross-analysis) of our own and literature data confirms the commonality and points to the universality of this metabolic mechanism for different forms of migration in fish ontogeny, which allows us to consider it as the most important aromorphosis type of phylogenetic adaptations, aimed at the species biological progress achieving. In the subsequent navigational mechanisms of homing, widely covered in the world literature, the leading role is played by the luliberinergic centers of the hypothalamus. The ecological diversity of these population-level mechanisms and the presence of straing in fish allow us to consider them as specializations of microevolutionary origin. The most promising direction for the further neuroendocrinological research development seems to be the analysis of the mechanisms of imprinting in connection with the enhancement of growth and survival of juveniles in the critical salinity medium, and for the purpose of homing control (development of the commercial fish-return biotechnology management) — the mechanisms of interaction between the NS and the luliberinergic centers in the neuroendocrine complex of CNS.