Post-exercise respirometry underestimates maximum metabolic rate in juvenile salmon
Climate change, metabolic scope, oxygen uptake, ram ventilation, thermal biology
Experimental biologists now routinely quantify maximum metabolic rate (MMR) in fishes using respirometry, often with the goal of calculating aerobic scope and answering important ecological and evolutionary questions. Methods used for estimating MMR vary considerably, with the two most common methods being (i) the 'chase method', where fish are manually chased to exhaustion and immediately sealed into a respirometer for post-exercise measurement of oxygen consumption rate (MO2), and (ii) the 'swim tunnel method', whereby MO2 is measured while the fish swims at high speed in a swim tunnel respirometer. In this study, we compared estimates for MMR made using a 3-min exhaustive chase (followed by measurement of MO2 in a static respirometer) versus those made via maximal swimming in a swim tunnel respirometer. We made a total of 134 estimates of MMR using the two methods with juveniles of two salmonids (Atlantic salmon Salmo salar and Chinook salmon Oncorhynchus tshawytscha) across a 6°C temperature range. We found that the chase method underestimated 'true' MMR (based on the swim tunnel method) by ca. 20% in these species. The gap in MMR estimates between the two methods was not significantly affected by temperature (range of ca. 15-21°C) nor was it affected by body mass (overall range of 53.5-236 g). Our data support some previous studies that have suggested the use of a swim tunnel respirometer generates markedly higher estimates of MMR than does the chase method, at least for species in which a swim tunnel respirometer is viable (e.g. 'athletic' ram ventilating fishes). We recommend that the chase method could be used as a 'proxy' (i.e. with a correction factor) for MMR in future studies if supported by a species-specific calibration with a relevant range of temperatures, body sizes or other covariates of interest.
Raby, Graham D.; Doherty, Claire L.J.; Mokdad, Ali; Pitcher, Trevor E.; and Fisk, Aaron T.. (2020). Post-exercise respirometry underestimates maximum metabolic rate in juvenile salmon. Conservation Physiology, 8 (1).