This document describes a procedure for the identification of single fish and fish fillets to the level of genus or species.
The identification of fish species is carried out by PCR amplification of either a segment of the mitochondrial cytochrome b gene (cytb)  or the cytochrome c oxidase I gene (cox1, syn COI) ,  or both, followed by sequencing of the PCR products and subsequent sequence comparison with entries in databases , . The methodology allows the identification of a large number of commercially important fish species.
The decision whether the cytb or cox1 gene segment or both are used for fish identification depends on the declared fish species, the applicability of the PCR method for the fish species and the availability of comparative sequences in the public databases.
This method has been successfully validated on raw fish fillets, however, laboratory experience is available that it can also be applied to processed, e.g. cold smoked, hot smoked, salted, frozen, cooked, fried, deep-fried samples.
This document is usually unsuitable for the analysis of highly processed foods, e.g. tins of fish, with highly degraded DNA where the fragment lengths are not sufficient for amplification of the targets. Furthermore, it is not applicable for complex fish products containing mixtures of two or more fish species.