Fig. 1. Premigratory gill Na⁺/K⁺-ATPase activity and future migratory behaviour in wild brown trout from the two tributaries (River Granslev Aa and Haldum Brook) in (A) late February–early March (163 future migrants and 25 future residents) and (B) mid-April (60 future migrants and 15 future residents). The solid line in B indicates the probability of future migration as a function of premigratory gill Na⁺/K⁺-ATPase activity, as determined by logistic regression analysis.