Comparison of Maximal Activities of Enzymes from Tissues of Thermally Acclimated and Naturally Acclimatized Chain Pickerel (Esox niger)

Maximal enzyme activities in tissues from 5 C- and 25 C-acclimated chain pickerel (Esox niger) were compared with those from winter- and summer-acclimatized fish to determine whether laboratory studies of thermal acclimation can be extrapolated to the natural environment. Activities of enzymes from pathways of aerobic metabolism measured at 15 C were higher in most tissues of cold-acclimated and winter-acclimatized pickerel than those in tissues of warm-acclimated and summeracclimatized fish, respectively, indicating that general patterns of metabolic response are similar in acclimated and acclimatized groups. Activities of enzymes in all tissues of summe- and winter-acclimatized fish were lower than activities in 25 C- and 5 C-acclimated fish. Activity of carnitine palmitoyltransferase (CPT), an indicator of the capacity for fatty-acid utilization, was higher in brain and red muscle tissue of cold-acclimated compared with warm-acclimated fish but was lower in winter-acclimatized compared with summer-acclimatized fish, indicating possible differences in metabolic fuel preferences between groups. Activity of creatine phosphokinase (CPK), indicating capacity for rapid ATP production, increased in red muscle tissue of winter-acclimatized compared with summer-acclimatized fish but did not change between acclimated groups. White muscle CPK activity increased in 5 C-acclimated compared with 25 C-acclimated fish but did not change between acclimatized groups. The results of CPK activity suggest that swimming-behavior differences between laboratory and natural environments may influence energy metabolism of the swimming musculature. Although general metabolic responses to temperature change may be extrapolated to the natural environment, environmental factors other than temperature-such as photoperiod and diet-may contribute to modification of these responses in certain tissues of naturally acclimatized fishes.