SEASONAL-VARIATION OF MUSCLE METABOLIC ORGANIZATION IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

This study examined how muscle metabolic organization varied during an annual cycle in which rainbow trout (Oncorhynchus mykiss) were held i n outdoor holding ponds in which they were exposed to natural changes in temperature (range 0.2 to 15.6 degrees C) and photoperiod. We exami ned the activities of glycolytic and mitochondrial enzymes in red and white muscle to evaluate whether trout enhance their capacity for lipi d and carbohydrate oxidation during cold-acclimization. When assayed a t habitat temperature, the enzyme activities generally increased in sp ring to reach a maximum in summer followed by a decrease in the fall. This led to significantly higher activities at warm than cold periods for all enzymes measured in red muscle and all but one in white muscle . The activities at 10 degrees C provided little evidence for compensa tory adjustments of aerobic capacity. Particularly in red muscle, enzy me levels at 10 degrees C were generally lower during cold than warm p eriods. The variation of enzyme activities throughout the cycle was no t due to changes in protein concentration, as the same responses were observed when activities were expressed per g wet mass or per mg prote in. Although the aerobic capacity did not increase with cold-acclimati zation, the relative capacity for lipid oxidation was higher in winter than in summer trout. In contrast, the relative capacity for aerobic glycolysis was higher in summer than in winter trout. Thus, the metabo lic capacities of trout muscle undergo seasonal reorganization.