Fig. 5. Enzymatic activities versus mRNA levels in liver of cold acclimated G. morhua. (A) Citrate synthase (CS); (B) Cytochrome c oxidase (COX). Enzyme activities (per g fresh mass; 10°C assay temperature) and mRNA levels (per g fresh mass) were normalized by setting the mean activity of warm-acclimated G. morhua from the North Sea population to 1. Cold acclimation led to increments in maximum activities of both enzymes, reflecting a higher aerobic capacity in the Arctic population. Citrate synthase activities were significantly correlated with the increase in mRNA levels in both populations, in line with transcriptional control of this enzyme. No such correlation was found for cytochrome c oxidase activity and COX2 mRNA levels despite a significant increase in mRNA levels for the Arctic population. Open circles, G. morhua (North Sea, NSC); filled triangles, G. morhua (north eastern Arctic Sea NEAC). Broken line, line of identity for COX (y=1.0x).