fishes that migrate for reproduction from seas to rivers (anadromous migration) or, less frequently, from rivers to seas (catadromous migration). Migratory fishes have a number of special features, such as the capacity to tolerate severe fluctuations in water salinity. The migrations provide favorable conditions for the development of the young and an abundant feeding base for the adults. At the same time, migrations require great expenditure of strength to overcome various obstacles (swift currents, rapids, waterfalls). The fishes accumulate the necessary energy reserves, mainly fat, in their bodies. Adult migratory fishes do not as a rule feed in rivers. After spawning, many migratory fishes, including salmon and herring, perish. Some species include winter and spring forms. Winter migratory fishes enter a river with immature sexual products. Their spawning grounds are usually located in the river’s upper course. Spawning occurs after the winter. Spring migratory fishes enter a river with almost mature sexual products and spawn in the same year; their spawning grounds are the river’s lower course.
Many migratory fishes are commercially valuable. For this reason, fish passages are made in dams when hydroelectric power plants are built. Migratory fishes are raised in fish hatcheries.
REFERENCESShmidt, P. Iu. Migratsii ryb, 2nd ed. Moscow-Leningrad, 1947.
Nikol’skii, G. V. Ekologiia ryb, 3rd ed. Moscow, 1974.
G. V. NIKOL’SKII