Temperature acclimation modulates the oxygen binding properties of the Atlantic cod (Gadus morhua L.) genotypes--HbI 1/1, HbI 1/2, and HbI 2/2--by changing the concentrations of their major hemoglobin components (results from growth studies at different temperatures)

The influence of long-term acclimation temperatures in Atlantic cod (Gadus morhua) was studied by growth experiments carried out over a total of 272 individuals. The attention focused on the structural and functional modulation of the five electrophoretically distinguishable genotypes of cod hemoglobin (HbI*1/1, HbI*1/2, HbI*2/2, HbI*1/2b, and HbI*2/2b) and on the correlation with body length/weight. The main results can be summarized as follows. (1) Acclimation to lower (4 and 8 °C) and higher (12 and 15 °C) temperatures favors the expression of, respectively, more anodic and more cathodic hemoglobin components. (2) The optimal O2 transporting features are observed at 12 °C, as well as a saturation-dependent temperature dependence of O2 binding, which furthermore is strongly dependent upon the acclimation background. (3) The optimal growth condition for the three main genotypes (HbI*1/1, HbI*1/2, and HbI*2/2) is associated with T=12 °C. The overall results are consistent with the idea that environmental temperatures constitute a primary factor in the aggregation of individuals physiologically more than genetically homogeneous. This is fully confirmed by careful statistical analysis carried out over a subset of individuals for which the full set of structural (isoelectric focusing), functional (O2 binding), and growth data was available.