Lipid corrections in carbon and nitrogen stable isotope analyses in freshwater fishes of the Paraná river, Argentina.

ALEJANDRA V. VOLPEDO; ADOLFO GIL; LLAMAZARES VEGH, SABINA

Viña del Mar

Conferencia; 11th International Conference on the Applications of Stable Isotope Techniques to Ecological Studies; 2018

Universidad Andrés Bello

Stable isotope analysis (SIA) coupled with mixing models are powerful tool for examining diet and food-web dynamics in aquatic ecosystems. Nitrogen isotopes can be used to determine trophic position, increasing about 3·4? at each trophic level. Carbon stable isotopes can be used to trace energy sources in food webs, because isotope values increase only slightly between diet and consumer (0?1?) during trophic transfers. Within an organism, lipids are depleted in 13C relative to proteins and carbohydrates, and variation in lipid content between species has the potential to increase variability in δ13C values. Despite the potential for introduced error, there is no consensus on the need to account for lipids in SIA. Several studies recommend accounting for lipids through chemical extraction prior to SIA or mathematical normalization when the lipid content in sample tissue is high (i.e., C:N >3.5, lipid content>5%) in fish muscle. While normalization models have been tested for some aquatic organisms, there has been no investigation of freshwater fauna of the Paraná river, the second largest river in South America. In this study, effects of lipid extraction and mathematical correction methods for eight freshwater fishes were compared to better understand impacts of normalization approaches on carbon (δ13C) and nitrogen (δ15N) stable isotope data. Following Sweeting lipid extraction, δ13C values were higher for all species with a mean increase of 0.36 ±0.23?. In contrast, there was a mean decrease in δ15N of 0.42 ±0.37. The lipid content ranged from 3.1% to 5.5% for Leporinus obtusidens and Cyphocharax voga, respectively. Only for C. voga the C:N >3.5 before treatment, extraction resulted in a decrease in C:N ratio and changes up to 1? in δ13C. For this species similar values of δ13C lipid-free were obtain using previous normalization models. The best fit relationship for δ13C was δ13C lipid-free= 0.88×δ13Cbulk?3.00 (R2=0.97; p