Mechanisms of downstream migration of young fish living in rivers
2007
Pavlov, D.S., Russian Academy of Sciences. The A. N Severtsov Inst. of Problems of Ecology and Evolution, Moscow (Russian Federation) | Lupandin, A.I. | Kostin, V.V., Russian Academy of Sciences. The A. N Severtsov Inst. of Problems of Ecology and Evolution, Moscow (Russian Federation)
A spatial segregation of roach larvae (stages C1-D1) was observed in the Volga River: in the daytime roach larvae were found in two habitats – under limno- and rheoconditions, while at night they were occurred in three habitats – under limno-, rheo-conditions and in the main stream. Catecholamine and corticosteroid concentrations were higher in migrants than in residents. The differences disappeared later, when roach downstream migration was over. Migrants and residents were distinguished by their metabolism: key enzymes of sympathetic adrenalin system; carbon and protein metabolism, participating in the forming and regulation of their energy state. The named differences in physiological and biochemical status of roach larvae mainly determined their behavior during migrations. Specific behavioral reactions could be observed at the decrease of illumination lower than 10 lux. They were typical of both migrants and residents, but differently directed: with the decrease of illumination, migrants chose zones with water currents, while residents chose zones with a calm water. The internal motivation had greater significance in realization of mecha¬nisms of downstream migration in young fish, than external conditions of orientation. Buoyancy determined main species-specific and age-specific peculiarities of fish distribution while turbulence modified it in accordance with hydrological conditions of water flows. In the concluded part of the book 3 types of the downstream migration of young freshwater fish are distinguished: not motivated downstream migration, motivated downstream migration and externally controlled downstream migration.
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