Abstract <p>During spawning migration and spawning, skeletal muscles of fish serve as a depot of plastic and energy substrates that are actively consumed to maintain viability. The content of water-soluble protein and its oxidized (carbonylated) fraction, as well as the activity of protein-hydrolyzing enzymes (intracellular proteases) in the skeletal muscles of pink salmon <i>Oncorhynchus gorbuscha</i> spawners during spawning migration from the White Sea to the Indera River have been characterized. At the initial stage of the migration route from the sea to the river, a reliable increase in the activity of cathepsin D, which plays a leading role in the degradation of muscle proteins, was noted in the skeletal muscles of pink salmon females, with no reliable quantitative changes in the soluble fraction of proteins. At the same time, during the spawning migration of pink salmon, accumulation of carbonylated proteins, markers of oxidative stress, was observed. It should be emphasized that the described changes are characteristic only of white skeletal muscles; in red muscles (aerobic, providing long-term swimming load), no changes were detected during spawning migration.</p>