Smoltification of hatchery-reared atlantic salmon (Salmo salar L.) – indices and methods of estimation

Abstract

Gill Na+-K+ATPase activity and body silvering were measured in one- and two-year old salmon. The data allowed to distinguish two fish groups in each age class: smolts and non-smolts. Discriminant functions were developed to qualify the fish into the groups. The values of these functions were assumed as the index of smoltification. Relationship between this index and detailed morphometric data indicates that smoltification involved head size decrease and body height increase in one-year old fish. In two-year old ones – lengthening and thickening of caudal peduncle was noted. These changes, however, were too little pronounced to enable accurate assessment of smoltification level, and silvering measurements were necessary.