BIOCHEMICAL CHARACTERISTICS OF MACROURID FISHES DIFFERING IN THEIR DEPTHS OF DISTRIBUTION

Abstract

Enzymic activities (units per gram wet weight of tissue) were measured in white skeletal muscle and brain tissue of five species of macrourid (rattail) fishes occurring over an approximately 5000 m depth gradient. Muscle protein and water contents were also determined. All species exhibited extremely low amounts of muscle enzymic activity for the glycolytic enzymes lactate dehydrogenase (LDH) and pyruvate kinase (PK), relative to values previously reported for shallow-living fishes. Malate dehydrogenase activity also was low, while citrate synthase (CS) activity was similar to levels found in shallow-living fishes. Interspecific differences among the rattails were large, especially for LDH activity which is a strong indicator of a fish's capacity for vigorous, burst swimming. Coryphaenoides armatus, a large rattail which is likely to be the most active swimmer among the species studied, had the highest enzymic activities and protein content, and, for LDH, PK, and CS, exhibited a significant scaling of enzymic activity with body mass. Scaling relationships were not observed for any other species. Brain enzymic activities were similar among all species. Muscle and brain enzymic activities also are reported for species belonging to four other deep-sea teleost families. The low levels of enzymes of energy metabolism found in skeletal muscle of these deep-sea fish species, and the interspecific variation in these activities are discussed in terms of the locomotory capacities and feeding strategies of these fishes. The potential usefulness of these types of enzyme data in estimating whole fish respiration rates is considered. We predict that the respiratory rates of the rattail species which have extremely low enzymic activity levels will be much lower than the respiratory rates previously measured for C. armatus.