Fig. 2. Gill Na⁺,K⁺-ATPase activity (µmol ADP mg^-1 protein h^-1) (A), plasma growth hormone levels (GH, ng ml^-1; B) and insulin-like growth factor I levels (IGF-I, ng ml^-1; C) in juvenile Atlantic salmon subjected to different temperature and photoperiod treatments (see Fig. 1). Values are means ± S.E.M. (N=12). Temperature increases in the advanced temperature group began on February 14 (arrowhead). There were significant effects of photoperiod, temperature and time on gill Na⁺,K⁺-ATPase activity and plasma IGF-I levels, and significant effects of photoperiod and time on plasma GH levels (P<0.05, three-way ANOVA). Vertical lines unconnected to other lines indicate a significant difference from other groups at that time point; time points with no vertical lines are not significantly different from one another (P=0.05, Kruskal-Wallis test).