Effects of lipid extraction on stable carbon and nitrogen isotope analyses of fish tissues: potential consequences for food web studies

We examined whether solvent‐based lipid extractions, commonly used for stable isotope analysis (SIA) of biota, alters δ 15 N or δ 13 C values of fish muscle tissue or whole juvenile fish. Lipid extraction from muscle tissue led to only small (<1‰) isotope shifts in δ 13 C and δ 15 N values. By contrast, ecologically significant shifts (+3.4‰ for δ 13 C and +2.8‰ for δ 15 N) were observed for whole juvenile fish. Sample variance was not affected by lipid extraction. For tissue‐specific SIA, two sample aliquots may be required: a lipid‐extracted aliquot for stable carbon isotope analysis when differing lipid content among tissues is a concern, and a nonextracted aliquot for δ 15 N determination. Whole organism SIA is not recommended because of the mix of tissues having different turnover times; for very small fish, we recommend that fish be eviscerated, decapitated, and skinned to minimise differences with samples of muscle tissue.