Exploring relationships between oxygen consumption and biologger-derived estimates of heart rate in two warmwater piscivores

Estimating metabolic rate in wild, free-swimming fish is inherently challenging. Here, we explored using surgically implanted heart rate biologgers to estimate metabolic rate in two warmwater piscivores, bowfin Amia calva (Linneaus 1766) and largemouth bass Micropterus salmoides (Lacepede 1802). Fish were surgically implanted with heart rate loggers, allowed to recover for 24 h, exposed to a netting and air exposure challenge, and then placed into respirometry chambers so that oxygen consumption rate ((M)over dot(O2)) could be measured in parallel to heart rate (f(H)) for a minimum of 20 h (ca. 20 estimates of (M)over dot(O2)). Heart rate across the duration of the experiment (at 19 degrees C) was significantly higher in largemouth bass (mean +/- s.d., 45 +/- 14 beats min(-1), range 18-86) than in bowfin (27 +/- 9 bpm, range 16-98). Standard metabolic rate was also higher in largemouth bass (1.06 +/- 0.19 mg O-2 kg(-1) min(-1), range 0.46-1.36) than in bowfin (0.89 +/- 0.17 mg O-2 kg(-1) min(-1), range 0.61-1.28). There were weak relationships between f(H) and (M)over dot(O2), with heart rate predicting 28% of the variation in oxygen consumption in bowfin and 23% in largemouth bass. The shape of the relationship differed somewhat between the two species, which is perhaps unsurprising given their profound differences in physiology and life history, illustrating the need to carry out species-specific validations. Both species showed some potential for a role of f(H) in efforts to estimate field metabolic rates, although further validation experiments with a wider range of conditions (e.g., digestive states, swimming activity) would likely help improve the strength of the (M)over dot(O2)-f(H) relationship for use in field applications.