Field metabolic rates of teleost fishes are recorded in otolith carbonate.

Field metabolic rate (FMR) is key to understanding individual and population-level responses to environmental changes, but is challenging to measure in field conditions, particularly in aquatic environments. Here we show that FMR can be estimated directly from the isotopic composition of carbon in fish otoliths (δC). We describe the relationship between δC values and oxygen consumption rate, and report results from laboratory experiments relating individual-level measurements of oxygen consumption rates to δC values in Atlantic cod ().