The use of ventilation frequency as an accurate indicator of metabolic rate in juvenile Atlantic salmon (Salmo salar)

Abstract

Bioenergetics studies of free-living animals have long been hampered by limitations on our abilities to measure the energy costs of different activities. Here we evaluate whether it is possible to use the opercular ventilatory beat rate of a fish to estimate its rate of energy expenditure. Changes in metabolic rate (MR) and ventilation rate (VR) were recorded in yearling Atlantic salmon ( Salmo salar , weight range 1.8–12.64 g) engaged in different activities at different temperatures while within a respirometer. MR was found to correlate strongly with VR in all fish. The relationship was linear, and both the slope and corresponding intercept of the regression equation were strongly dependent on the fish’s body weight and the test temperature. From these relationships, a general equation was generated to predict MR at a range of temperatures from knowledge of a fish’s weight and its VR; this proved to be highly accurate (correlation between predicted and observed MRs: r = 0.95), although calibration of individual fish is recommended in studies that compare performance of individuals. Visual measurements of VR may therefore provide a highly accurate, cheap, and noninvasive method of measuring the energy consumption of fish engaged in natural behaviours in more natural settings.