Relationship between Na+,K+-ATPase activity and migration behaviour of brown trout and sea trout (Salmo trutta L.) during the smolting period

Gill Na+,K+-ATPase activity was determined on three occasions (11 May, 30 M ay, 11 July) from PIT-tagged 2-year-old brown and sea trout (Salmo trutta), whose smelt migration was monitored in an annular flume tank. Of these thr ee occasions, gill Na+,K+-ATPase activity was highest at the end of May coi ncidentally with the highest activity of downstream migration. Na+,K+-ATPas e activity was significantly higher in brown trout than in sea trout in the end of May, but on the other two dates, there were no differences. There w ere no statistically significant correlations between the Na+,K+-ATPase act ivity and downstream migration at an individual level. The present result s uggests that even if there is a general tendency for the elevation in gill Na+,K+-ATPase activity of two forms of S. trutta during the smolting period , this does not necessarily occur simultaneously with the changes in downst ream migration behaviour at an individual level. (C) 1998 Elsevier Science B.V. All rights reserved.