Best BLAST hit alone cannot be used as evidence of fraud

Abstract In a recent study, Blanco-Fernandez, et al. 1 applied molecular tools to authenticate fish products and conclude evidence of “worrying international fraud”. They revealed mislabeling in recognizable and unrecognizable fish products labeled as anchovy, hake and tuna commercialized by European companies. Their analyses consisted on extracting DNA from the fish product to be authenticated followed by amplification and sequencing of a suite of DNA markers and on comparing the resulting sequences to the GenBank sequence database using BLAST (Basic Tool Alignment Search Tool) ( https://blast.ncbi.nlm.nih.gov/Blast.cgi ). By carefully reanalyzing their data, we identify errors in their species identification and conclude that best BLAST hit alone cannot be used as evidence of fraud.