Molecular aspects of temperature acclimation in fish: Contributions of changes in enzyme activities and isozyme patterns to metabolic reorganization in the green sunfish

Spectrophotometric and electrophoretic techniques were used to monitor qualitative and quantitative aspects of changes in 12 enzymes from five different tissues of green sunfish after thermal acclimation. Changes in dissolved oxygen concentrations over the range 5–25 ppm had no significant effect on qualitative or quantitative aspects of enzyme distributions. In response to differences in environmental temperature, however, significant changes in the levels of activity of fructose‐biphosphate aldolase, pyruvate kinase, lactate dehydrogenase, malate dehydrogenase, succinate dehydrogenase, cytochrome oxidase, cytochrome c, and glucose‐6‐phosphate dehydrogenase were observed in one or more tissues. Enzymes in a single metabolic pathway (e.g., glycolysis) usually exhibited parallel changes in a given tissue. Enzymes in different pathways, on the other hand, frequently exhibited changes in opposite directions, one group of enzymes increased in the cold while the other group decreased, indicating that major metabolic reorganizations were occurring. The patterns of change among tissues were distinctly different, therefore changes observed in one tissue cannot readily be generalized to other tissues. No changes in isozyme patterns were seen for lactate dehydrogenase, creatine kinase, fructose‐biphosphate aldolase, malate dehydrogenase, glucosephosphate isomerase, phosphoglucomutase, glycerol‐3‐phosphate dehydrogenase, or alcohol dehydrogenase in any of the tissues examined. However, some changes in the isozyme patterns of esterases in both liver and eye tissue were observed. These observations indicate that major changes in isozyme repertories do not necessarily accompany the thermoacclimatory responses of all fishes.