ered mislabelled. When only the commercial name was present, mislabelling records were obtained by following each country's list of approved commercial designation for tunas ([S2 Table](#pone.0196641.s002){ref-type="supplementary-material"}). When the scientific name was present, it was the one taken as a reference to compare with the analytical result.

Statistical analysis {#sec006}
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Software GraphPad Prism was used to perform pairwise comparisons between data sets using Chi-square with Yate's correction and correlation analysis for the dependence between number of samples and mislabelling rate.

Results and discussion {#sec007}
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545 tuna samples--of which 225 fresh & frozen, 268 canned and 52 miscellaneous (e.g. dried, roes, salads etc.)--were successfully sequenced and identified (for more detailed information about the results of previous tuna species identification ring trials see [S1 File](#pone.0196641.s008){ref-type="supplementary-material"}); 37 of them were mislabelled, making an overall mislabelling rate of 6.79% ([Fig 1](#pone.0196641.g001){ref-type="fig"}). This study is not only the largest sampling effort reported for tuna products but also one that involves six different European countries. Previously reported mislabelling rates for tuna were very variable, on average 18% \[[@pone.0196641.ref015]\], mainly because these rates may change over time and also because the type of retailer or provenance of samples influence dramatically the results obtained. The much lower value found here may be an indication of the impact of labelling legislation and control, the mass media coverage of food fraud with the consequence of consumer being more aware of food labels \[[@pone.0196641.ref008]\].

![Collected samples and mislabelling rate for tuna seafood products across six European countries.\
Fig 1A: Number of collected samples and mislabelling rates (red bars) for all analysed tuna products in six European countries. Statistical differences are shown by letters,