By combining physiological and morphological methods with available and emerging molecular biology methods, we can now begin to understand adaptation to altered environmental conditions at the gene level. Fish are ectotherms and are therefore expected to be directly affected by temperature changes in water temperature. However, in our work we have found that some species are not completely at the mercy of the environment, as they can rebuild their muscle contractile apparatus for low temperature or for warm temperature swimming. They achieve this by expressing different sets of myofibrillar protein isogenes at different environmental temperatures.

Ectothermy is sometimes considered to be a more primitive state than endothermy. These states can more correctly be regarded as evolutionary options and it depends whether economy is more important than high locomotory speed for the survival of the species. Certainly, the resulting extra performance at the higher body temperature is expensive, as this has to be maintained all the time in all mammals and birds except during hibernation. In ectotherms in a few cases, extra performance is achieved by retaining heat generated by the locomotory muscles using a countercurrent heat exchanger or retina system, the examples, the eye heater organ and the myotomal muscle in tuna. In carp and similar fish species the evolutionary strategy has not been to raise the tissue temperature. Instead, by expressing a different set of genes, the enzyme system is changed so that it is optimized to the tissue temperature, which remains essentially the same as the ambient temperature.