Oxygen Consumption of Desert Pupfish at Ecologically‐Relevant Temperatures Suggests a Significant Role for Anaerobic Metabolism

Abstract

Oxygen consumption is oftentimes used as a proxy for metabolic rate. Routine oxygen consumption (RVO2) of a refuge population of Cyprinodon diabolis acclimated to ecologically relevant temperatures of 28 °C and 33 °C was evaluated at assay temperatures between 25 °C and 38 °C. Different interpretations of the data are available depending on normalization. For instance, RVO2 of smaller fish, measured per fish, was remarkably stable over a wide range of assay temperatures and was not different between acclimation groups. Measured on a mass‐specific basis, RVO2 in larger fish increased more predictably as temperature increased. RVO2 of refuge fish and the closely related pupfish, C. nevadensis mionectes, measured near their respective acclimation temperatures of either 28 °C or 33 °C were essentially identical. However, RVO2 of 28 °C acclimated fish of both species, when measured at 33 °C, was greater than that of the 33 °C acclimated fish measured at 28 °C. We suggest this observed ‘efficiency’ may result from significant anaerobic metabolism use. Experiments investigating metabolic scope (MaxVO2/RVO2) yielded values less than 1 in 33 °C acclimated fish. These values indicate a substantial contribution of anaerobic metabolism to energy utilization by these fish. However, muscle lactate levels are not elevated in exercising fish‐ a result that is consistent with paradoxical anaerobism use.Support or Funding InformationSupported by grants from the US Fish and Wildlife Service and Nevada Department of Wildlife