Estimation of smoltification of hatchery-reared sea trout (Salmo trutta morpha trutta L.) based on body morphology

Abstract

Detailed morphometric studies (truss network) were carried out using one and two years old sea trout. Additionally, body silvering and condition factors were evaluated. Correlation of these data (in various combinations) with smoltification index calculated from gill Na+-K+-ATPase activity and silvering (Dębowski et al. 1999b) were calculated as well as regression coefficients. Smoltification involved slight changes in fish body proportions: a decrease of head size, body height, and an increase of caudal part. These changes were, however, not sufficient to evaluate the degree of smoltification. Taking into consideration also body length and condition factor it was possible to develop regression model which explained 66% of smoltification index variation in one year old fish, and 57% - in two year old ones. Using additionally silvering value, increased coefficients of determination of the models to 98 and 99% respectively.