(a) Maximum number and (b) average diameter of fast muscle fibres in Atlantic cod (Gadus morhua) with different haemoglobin phenotypes. In (a) mean+s.e., 12 HbI-(1/1), 19 HbI-(1/2) and 18 HbI-(2/2) phenotypes, **indicates significant difference p<0.01. In (b) HbI-(1/1) phenotypes (open symbols), HbI-(2/2) phenotypes (closed symbols), PanI-(A/A) genotypes (circles), PanI-(A/B) genotypes (triangles). First order regression lines were fitted: HbI-2/2 (solid line), HbI-1/1 (dotted line). Insert shows a typical RT-PCR gel for PanI genotypes with positive and negative controls.