The body size and weight characteristics were analyzed and the morpho-physiological condition of the system of internal organs was studied in wild juvenile pink salmon caught from five rivers during downstream migration, as well as in hatchery-reared juveniles collected prior to release from all 22 salmon hatcheries of Sakhalin Oblast where they were produced in 2016 and 2017. It was found that the body weight of wild juvenile pink salmon from different rivers and in different years varied significantly. Hatchery-reared fry before release were 1.5–2.5 times larger than wild ones on average; at different hatcheries, the body weight of fry closely correlated with the sum of the accumulated degree-days. All fry from natural spawning grounds during the downstream migration had remnants of a yolk sac, although some of them were already actively feeding in fresh water. Hatchery-reared fry, irrespective of their growth rate, also retained yolk sac remnants before release. In all groups of wild and hatchery-reared juveniles different variants of the micromorphological organization of hepatic parenchyma were identified.