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

摘要

Although 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 (50-130mm FL) influence preservation-induced changes in C-13 and N-15. In both species, we found that treatment fins (frozen and later preserved in ethanol) exhibited higher C-13 than did paired reference fins (frozen). The changes in N-15, however, were smaller in magnitude and less consistent. Preservation-induced increases in fin C-13, but not N-15, were significantly correlated with the change in C:N ratio (treatment-reference) in both species. In addition, these increases in C-13 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 C-13 and a small, but insignificant, effect on N-15 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 C-13 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.