Abstract
This study investigated the impact of lipid extraction, CaCO 3 removal and of both treatments combined on fish tissue δ 13 C, δ 15 N and C:N ratio. Furthermore, the suitability of empirical δ 13 C lipid normalization and correction models was examined. δ 15 N was affected by lipid extraction (increase of up to 1·65‰) and by the combination of both treatments, while acidification alone showed no effect. The observed shift in δ 15 N represents a significant bias in trophic level estimates, i.e. lipid‐extracted samples are not suitable for δ 15 N analysis. C:N and δ 13 C were significantly affected by lipid extraction, proportional to initial tissue lipid content. For both variables, rates of change with lipid content (ΔC:N and Δδ 13 C) were species specific. All tested lipid normalization and correction models produced biased estimates of fish tissue δ 13 C, probably due to a non‐representative database and incorrect assumptions and generalizations the models were based on. Improved models need a priori more extensive and detailed studies of the relationships between lipid content, C:N and δ 13 C, as well as of the underlying biochemical processes.