Adaptation of cultured salmon Salmo salar (Salmonidae) yearlings to natural environments

Abstract

The process of adaptation of the yearling Atlantic salmon Salmo salar cultured under the farming conditions in the Umba fish hatchery to the natural environments has been studied during a 1-year period after releasing them into the river. The significant differences in a range of the morphophysiological parameters between the hatchery-reared juveniles and their wild-origin peers, which were revealed immediately before the release into the river and 1 month later, are gradually reduced. The index of body condition, the liver index, and the body cavity fat content are normalized 4 months later; 13 months later, the other analyzed parameters (the hemoglobin concentration and the indices of heart, gills, and pectoral fins) are brought back into the normal ranges. The behavioral patterns of the hatchery-reared and wild-origin juveniles remain different during the whole observation period, since the behavioral habits acquired under the farming conditions, when compared to the developmental abnormalities, more commonly affect the juvenile fish survival in the natural environments.