CONTRIBUTIONS TO TEMPERATURE ADAPTATION OF EEL (ANGUILLA VULGARIS) .3. INTENSITY AND DISTRIBUTION OF ACTIVITY OF SUCCINATE DEHYDROGENASE AND CYTOCHROME OXIDASE IN LATERAL MUSCLE OF JUVENILE AND ADULT ANIMALS

Previous authors have demonstrated that changes in O2-consumption of predominant muscle tissue (in vitro) do not account for the variations in O2-consumption of a resting intact eel induced by differences in adaptation temperature (AT). The present paper is concerned with the metabolism of the eel's lateral muscle. Activity of cytochrome oxidase and succinate dehydrogenase, expressed in terms of O2-consumption, are higher in the red muscle portion than in the white one (the factors are 6 to 10 and 2 to 3, respectively). In epaxial muscle strips from some 10 cm behind the anus, red muscle tissue comprises between 44% and more than 60% of the total lateral muscle cytochrome oxidase activity, even though, in this region, the relative weight of the red portion makes up only 11 to 14.5% of the total muscle. The red muscle portion is still smaller in the region anterior to the anus, and its total cytochrome oxidase activity (enzyme activity x relative weight) much lower. Cytochrome oxidase activity remains rather unchanged in the white portion of the muscle. Since the metabolism of white muscles is primarily glycolytic, it is remarkable that - with respect to the terminal oxidative metabolism - tissue temperature adaptation in the eel is more pronounced in red muscles than in white ones. In juvenile and adult eels, acclimated to seasonal temperature, the total cytochrome oxidase activity of the white muscle undergoes little change. However, in cold-acclimated adults with extensive pigmentation, aerobic metabolism of red muscles is favoured; this is indicated both by extremely high cytochrome oxidase activity and increased relative muscle weight. Increased aerobic metabolism of red muscle tissue is, therefore, assumed to be important, especially during the winter spawning migration. © 1969 Springer-Verlag.