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 delta(15)N or delta(13)C values of fish muscle tissue or whole juvenile fish. Lipid extraction from muscle tissue led to only small (<1%) isotope shifts in delta(13)C and delta(15)N values. By contrast, ecologically significant shifts (+3.4% for delta(13)C and +2.8% for delta(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 delta(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.