Over the last few years, molecular species identification has revealed high levels of seafood mislabelling, which has generated public concern. The success of regulatory efforts depends on the accurate estimation of species substitution across multiple points in the supply chain. Flounders are among the most popular and highly valued seafood products marketed in Brazil. However, substitution rates are poorly known in large consumer markets such as Rio de Janeiro. We used sequences of mitochondrial genes to estimate the prevalence of mislabelling in the Brazilian flounder trade. Nearly 50 % (130/260) of fish samples analysed were mislabelled. The prevalence of mislabelling varied across the commercialisation chain and was high in street markets (61 %) and restaurants (82 %), when compared to fishmongers (38 %) and supermarkets (22 %). The most common species used as substitutes were Pangasianodon hypophthalmus (75 %) and Xystreurys rasile (17 %). We show that the 2015 revisions were ineffective in reducing mislabelling and curb inspection by omitting frequently commercialized local pleuronectiforms, such as X. rasile. Substitute species were usually lower-priced, indicating an economic motivation for mislabelling. Our findings reinforce the need for updated and consistent labelling regulations and more stringent control of flounder sales in street markets and restaurants.

在过去的几年里，分子物种鉴定揭示了大量的海产品贴错标签，这引起了公众的关注。监管工作的成功取决于对供应链中多个点的物种替代的准确估计。比目鱼是巴西销售的最受欢迎和价值最高的海鲜产品之一。然而，替代率在里约热内卢等大型消费市场鲜为人知。我们使用线粒体基因序列来估计巴西比目鱼贸易中错误标记的普遍性。近 50% (130/260) 的分析鱼样品被贴错了标签。错误标签的发生率在整个商业化链中各不相同，与鱼贩 (38%) 和超市 (22%) 相比，街头市场 (61%) 和餐馆 (82%) 的比例较高。Pangasianodon hypophthalmus (75 %) 和Xystreurys rasile (17 %)。我们表明，2015 年的修订通过省略经常商业化的本地胸膜结节类（如X. rasile ）在减少错误标签和遏制检查方面无效。替代物种的价格通常较低，表明贴错标签的经济动机。我们的研究结果强调了更新和一致的标签法规以及对街头市场和餐馆中比目鱼销售进行更严格控制的必要性。