Field metabolic rates of wild marine fishes: reviewing old questions with new data.

Abstract

Time integrated Field Metabolic Rate (FMR) is arguably the most ecologically relevant measure of the energetics of wild animals, but the relative complexity of determining FMR routinely means that we have relatively few large datasets describing variation in energy use in free-living wild animals, particularly for aquatic ectotherms where double labelled water methods cannot be used. Emerging proxies based on stable isotope systematics associated with respiration allow retrospective estimation of time integrated field metabolic rate, experienced temperature and growth in any free living marine teleost fish. We have estimated FMR in over 1000 individual fish, across nearly 100 species. Here we draw on our data compilation to explore predictions for two contentious topics in fish ecophysiology: (1) Metabolic cold adaptation: We show that polar species have higher FMR than temperate but not tropical species at equivalent body sizes and temperatures, and that, within species, populations at the cold edge of the range express higher FMR but lower growth rates than populations at the warm edge of the species range. (2) Gill oxygen limitation theory: FMR data covering 4 orders of magnitude body size within single species show no strong evidence for reduction in metabolic capacity at large body sizes as predicted by the GOLT.