The Effects of Ethanol Preservation on Fish Fin Stable Isotopes: Does Variation in C:N Ratio and Body Size Matter?

Abstract

AbstractAlthough chemical preservation of stable isotope samples has been studied in a variety of species and tissue types, the effects of ethanol preservation on fish fin tissue have not been examined. Using caudal fin samples from juvenile Chinook Salmon Oncorhynchus tshawytscha and Rainbow Trout O. mykiss or steelhead (the anadromous form of Rainbow Trout), we investigated how storage time (2, 4, and 6 months), fin composition (C:N ratio), and fish body size (50–130 mm FL) influence preservation‐induced changes in δ13C and δ15N. In both species, we found that treatment fins (frozen and later preserved in ethanol) exhibited higher δ13C than did paired reference fins (frozen). The changes in δ15N, however, were smaller in magnitude and less consistent. Preservation‐induced increases in fin δ13C, but not δ15N, were significantly correlated with the change in C:N ratio (treatment–reference) in both species. In addition, these increases in δ13C were more highly correlated with body size in O. mykiss than in Chinook Salmon. Storage time had a significant effect on the shift in treatment fin δ13C and a small, but insignificant, effect on δ15N in O. mykiss. However, storage time was not a significant factor for explaining the isotopic shifts observed in Chinook Salmon fin tissue. This is the first study to document variation in preservation‐induced changes in δ13C within a species and to link this variation to C:N ratio. Future studies using species‐specific and tissue‐specific models to correct for preservation‐induced shifts in stable isotope ratios should be aware that these models do not account for intraspecific variation in tissue composition.