Parameters of energy metabolism in juveniles of Atlantic salmon <Emphasis Type="Italic">Salmo salar</Emphasis> living in the mainstream and in the tributary of the Varzuga River (the Kola Peninsula)

In juveniles of Atlantic salmon Salmo salar of two age groups (0+ and 1+) living in the mainstream and in the tributary of the subarctic Varzuga River, the activity of some enzymes was determined (cytochrome c oxidase, malate dehydrogenase, lactate dehydrogenase, glucose-6-phosphate dehydrogenase, and 1-glycerophosphate dehydrogenase), reflecting the intensity of the direction of principal pathways of carbohydrate metabolism and of synthesis of ATP. The effect of environmental conditions on growth and development of different age groups is different. Underyearlings (0+) living in the tributary are characterized by an advanced locomotor performance and growth rate. They possess a higher level of aerobic and anaerobic energy metabolism and assimilation of carbohydrates for synthesis of structural and stock compounds in comparison with yearlings living in the mainstream. No significant differences are found between two-summer-old fish (1+) from different habitats in parameters of energy metabolism. This demonstrates that the living conditions for them in the tributary are not so favorable as from underyearlings. The food items in the tributary are small and numerous, i.e., are more available for salmon underyearlings. Parrs 1+ feed on large invertebrates and feeding in the mainstream is preferable. The differences in parameters of energy metabolism of juvenile salmon manifesting themselves in the first year of life make the basis for the fact that the subsequent smoltification of parrs and migration for feeding occur at different ages—2+, 3+, or 4+. This contributes to the formation of the complex age structure of the Varzuga stock of salmon.