Fatty acids are widely used to study trophic interactions in food web assemblages. Generally, it is assumed that there is a very small modification of fatty acids from one trophic step to another, making them suitable as trophic biomarkers. However, recent literature provides evidence that many fishes possess genes encoding enzymes with a role in bioconversion, thus the capability for bioconversion might be more widespread than previously assumed. Nonetheless, empirical evidence for biosynthesis occurring in natural populations remains scarce. In this study, we investigated different feeding types of perch (Perca fluviatilis) that are specialized on specific resources with different levels of highly unsaturated fatty acids (HUFAs), and analyzed the change between HUFA proportions in perch muscle tissue compared to their resources. Perch showed matching levels to their resources for EPA, but ARA and especially DHA were accumulated. Compound-specific stable isotope analyses helped us to identify the origin of HUFA carbon. Our results suggest that perch obtain a substantial amount of DHA via bioconversion when feeding on DHA-poor benthic resources. Thus, our data indicate the capability of bioconversion of HUFAs in a natural freshwater fish population.

脂肪酸被广泛用于研究食物网组件中的营养相互作用。通常，假定脂肪酸从一个营养步骤到另一个营养步骤的修饰很小，使其适合用作营养生物标记。然而，最近的文献提供了证据，表明许多鱼类拥有编码在生物转化中起作用的酶的基因，因此生物转化的能力可能比以前设想的更为广泛。然而，自然人口中发生生物合成的经验证据仍然很少。在这项研究中，我们调查了不同种类的鲈鱼（Perca fluviatilis））专门研究具有不同水平的高度不饱和脂肪酸（HUFA）的特定资源，并分析了鲈鱼肌肉组织中HUFA比例与其资源之间的比例变化。鲈鱼显示出与EPA的资源相匹配的水平，但是ARA尤其是DHA积累了。化合物特定的稳定同位素分析帮助我们确定了HUFA碳的来源。我们的结果表明，当以缺乏DHA的底栖动物为食时，鲈鱼可通过生物转化获得大量DHA。因此，我们的数据表明了天然淡水鱼种群中HUFAs的生物转化能力。