In order to investigate the metabolic regulation in Atlantic salmon fries (Salmo salar L.) during their growth, development, and in the course of size divergence, age-related changes in the activity of enzymes involved in the energy and carbohydrate metabolism, including myosin heavy chain isoform expression, RNA/DNA ratio in the white muscles and liver of specimens at ages of 0+; 1+, and 2+, as well as correlations of these characteristics with the body weight of fish specimens were analyzed. Multidirectional changes in the activity of enzymes taking part in aerobic and anaerobic energy metabolism, as well as a decrease in the protein synthesis with age, were revealed. There was a positive correlation between the activities of cytochrome oxidase, lactate dehydrogenase, aldolase, and myosin gene expression in the muscles, cytochrome oxidase activity, glucose-6-phosphate dehydrogenase, and glycerol-3-phosphate dehydrogenase in the liver with the body weight of salmon specimens within the age groups.