Lipid correction of hydrogen stable isotope ratios in fish

Abstract Lipids are known to affect stable isotope ratio of organisms, especially δ 13 C values, and simple arithmetic lipid‐correction procedures have been developed based on the carbon to nitrogen ratio (C : N) that is a proxy for lipid content. Equivalent issues will likely arise with the increasing use of hydrogen isotopes in ecology, but as yet no procedure has been available to handle this. We extracted lipids from muscle and from whole fish using a standard chemical extraction procedure. Using isotope ratio mass spectrometry, we then compared the δ 2 H values of untreated tissues, lipid‐extracted tissues, and the extracted lipids. In the process of performing carbon and nitrogen stable isotope analysis on the same sample, elemental data on carbon and nitrogen content were obtained simultaneously. Using these data, we determined the relationship between lipid concentration and C : N. Extracted lipids were strongly depleted in the heavy isotope of hydrogen, so that tissues from which lipids had been extracted had higher δ 2 H values than those of untreated tissues. The lipid content of the samples was directly related to their C : N, so the change in tissue δ 2 H values following lipid extraction was also strongly dependent on tissue C : N. This strong dependence allowed the development of a simple arithmetic procedure to correct δ 2 H values for variations in tissue lipid content. Arithmetic correction offers a way to normalize δ 2 H values from animal tissues with respect to the variations in lipid content and can find wide application in ecological studies using hydrogen isotopes.