BIOCHEMICAL INDEXES OF AEROBIC AND ANAEROBIC CAPACITY IN MUSCLE TISSUES OF CALIFORNIA ELASMOBRANCH FISHES DIFFERING IN TYPICAL ACTIVITY LEVEL

Biochemical indices of aerobic and anaerobic metabolic capacity were m easured in white myotomal muscle of eight marine elasmobranch fish spe cies representing a broad range of locomotor performance, and in red m yotomal muscle and heart of three of those species. The objectives wer e to determine if metabolic capacities vary with typical fish activity level, to compare the endothermic mako shark with ectothermic pelagic sharks, and to compare elasmobranchs with teleosts in order to test t he hypothesis that elasmobranchs have lower aerobic capacities, metabo lic rates, and swimming speeds. In white myotomal muscle, activities o f the enzymes citrate synthase (an index of aerobic capacity), pyruvat e kinase, and lactate dehydrogenase (LDH, an index of anaerobic capaci ty) covaried with typical activity level, and the ability to tolerate intracellular acidification (nonbicarbonate buffering capacity) corres ponded with LDH activity. Enzyme activities in red muscle and heart di d not show a consistent pattern with respect to fish activity. In comp arison with ectothermic sharks, the mako shark had greater aerobic and anaerobic capacities in white muscle, but no significant differences were found in red muscle or heart. This pattern has also been found in teleosts. Thus, endothermic fishes elevate the temperature of red mus cle, a tissue specialized for high aerobic performance, whereas white muscle biochemical characteristics are adjusted to support high rates of contraction both aerobically and anaerobically. Muscle enzymic acti vities of elasmobranchs and teleosts with comparable locomotor habits are similar, thus refuting the hypothesis that elasmobranchs are slugg ish, with lower metabolic capacities than teleosts.