Meeting Abstract
Enzyme activity can be used as an index of aerobic or anaerobic capacity when it is difficult or impossible to measure metabolic rate or maximal activity directly, as with large sharks. The purpose of this study was to compare the activities of key metabolic enzymes in the fast-glycolytic locomotor muscles of shark species from a range of depths and predicted levels of locomotor activity. Four previously unstudied shark species, and additional individuals of two other species, were sampled, and combined with comparable published data. Interspecific comparisons using this combined database allowed more robust tests of hypotheses concerning relationships among enzyme activity, phylogeny, fish activity level, and depth of occurrence. For this study, sharks were collected using long lines, and muscle was sampled with an 8mm biopsy needle, frozen in liquid nitrogen aboard ship, and stored at -80°C for up to 12 months prior to analysis. Spectrophotometric assays were used to quantify the maximal activity (at saturating substrate concentrations) of four enzymes that catalyze reactions in the metabolic pathways for both aerobic and anaerobic ATP production: citrate synthase, malate dehydrogenase pyruvate kinase, and lactate dehydrogenase. There was a much wider range in enzyme activities in the shallow-living species than in the deep-water species, and the highest activities were found in regional endotherms and active swimmers. Activities of all four enzymes generally decreased with depth, corresponding with differences between shallow- and deep-water elasmobranch in locomotor capacity and ecological strategies. These findings parallel results for teleost fishes and cephalopods.
