The Maintenance of Different Enzyme Activity Levels in Congeneric Fishes Living at Different Depths

To determine the influence of depth-related factors on enzymic activity and, hence, on metabolism, we measured enzymic activities of white skeletal muscle and brain in two teleost fishes of the genus Sebastolobus (Scorpaenidae). These species are genetically close and have similar life histories but differ in their depth distributions. White skeletal muscle of the shallow-living species, S. alascanus, contained approximately twice the activity (measured as units per g wet weight of tissue) of lactate dehydrogenase (LDH), pyruvate kinase (PK), malate dehydrogenase (MDH), creatine phosphokinase (CPK), and citrate synthase (CS) as the white muscle of the deep-living species, S. altivelis. The CS and LDH activities exhibited body-sizerelated scaling; CS activity decreased and LDH activity rose in larger-sized specimens. The interspecific activity differences may derive either from differences in substrate turnover number (e.g., LDH) or from differences in enzyme concentration (e.g., PK). Through these two act...