Chasing away accurate results: exhaustive chase protocols underestimate maximum metabolic rate estimates in European perch Perca fluviatilis

Abstract

Metabolic rates are one of many measures that are used to explain species' response to environmental change. Static respirometry is used to calculate the standard metabolic rate (SMR) of fish, and when combined with exhaustive chase protocols it can be used to measure maximum metabolic rate (MMR) and aerobic scope (AS) as well. While these methods have been tested in comparison to swim tunnels and chambers with circular currents, they have not been tested in comparison with a no-chase control. We used a repeated-measures design to compare estimates of SMR, MMR and AS in European perch Perca fluviatilis following three protocols: (a) a no-chase control; (b) a 3-min exhaustive chase; and (c) a 3-min exhaustive chase followed by 1-min air exposure. We found that, contrary to expectations, exhaustive chase protocols underestimate MMR and AS at 18°C, compared to the no-chase control. This suggests that metabolic rates of other species with similar locomotorty modes or lifestyles could be similarly underestimated using chase protocols. These underestimates have implications for studies examining metabolic performance and responses to climate change scenarios. To prevent underestimates, future experiments measuring metabolic rates should include a pilot with a no-chase control or, when appropriate, an adjusted methodology in which trials end with the exhaustive chase instead of beginning with it.

Keywords: aerobic scope; climate change; exhaustive chase; intermittent-flow respirometry; methods; standard metabolic rate.

FIGURE 1

Schematic view of the experimental design: maroon, no‐chase; yellow, chase; blue, chase + air

FIGURE 2

Boxplots showing the median and interquartile range of (a) standard metabolic rate (SMR, calculated from the lowest 10% of ṀO₂ measures), (b) maximum metabolic rate (MMR, the global maximum ṀO₂ measurement) and (c) aerobic scope (AS, calculated as MMR – SMR) measured in each of the three treatments: maroon, no‐chase; yellow, chase; blue, chase + air. Different letters indicate significant differences (α = 0.05)