Gill Na+-K+ ATPase activity and body silvering as indices of smoltification of hatchery-reared sea trout (Salmo trutta m.trutta L.)

Abstract

Gill Na+-K+ ATPase activity and body silvering were studied in spring in one- and two year old sea trout (Salmo trutta m.trutta L.), under hatchery conditions. Two groups were distinguished in each age-class: smolts and non-smolts. Smolts of both age classes showed higher ATPase activity, lower condition coefficient, and more distinct body silvering. One year old smolts were also longer, and their bodies contained more fat compared to non-smolts. In two years old smolts lower fat level was observed. Discriminant functions were proposed, taking into consideration ATPase activity and body silvering, to distinguish smolts from non-smolts. These functions may be used as a smoltification index.