Small minnows from the genus Phoxinus (Leusciscidae) inhabit diverse habitats, such as mountain streams, lowland rivers as well as different types of lakes. While initially several species were described, they were united under one, widely spread species, Phoxinus phoxinus or European minnow. For over a century, the taxonomy remained unchanged, until morphological studies re-established or newly described several species. Subsequently, molecular studies followed (mostly based on the barcoding region of the cytochrome oxidase I (COI)) and exposed an unexpected biodiversity of the genus. Phoxinus phoxinus is a complex of species that up until now includes 23 genetic lineages, thirteen of which are considered valid species.

Similarly, as in Europe, Austria was believed to be populated with P. phoxinus. However, genetic studies have shown that three additional species inhabit Austrian waters, namely P. csikii, P. lumaireul and P. marsilii. Moreover, three sublineages of P. lumaireul have been identified. It was not clear, which of the lineages/species occur naturally and which were introduced. Thus, comparison of the museum material dating as far as 200 years back and freshly collected samples was used to evaluate the distribution of genetic lineages. The results suggested that P. csikii, P. marsilii and two sublineages of P. lumaireul occur naturally, while P. phoxinus and one sublineage of P. lumaireul have been introduced.

The amazing biodiversity of the Phoxinus genus came to light using two mitochondrial genes, proving once more their usefulness to establish an inventory of the biosphere through barcoding. Nevertheless, there are also important pitfalls of the method, which are too often diminished. The barcoding gene offers only one version of evolutionary history, which is yet to be corroborated with nuclear markers. In addition, the reduced sampling performed in the frame of a barcoding project would not suffice to detect the complete biodiversity of Phoxinus. On one hand, a bigger reference base is needed to observe the formation of two different clades, when comparing closely related P. lumaireul and P. csikii. On the other hand, P. marsilii has its most western distribution point in the surrounding of Vienna, and hence has a very restricted distribution in Austria, which easily could have been overseen. Finally, due to frequently detected anthropogenic translocations, it would be difficult to discriminate between natural and human induced distribution. Thus, barcoding can certainly be used as a first step in biodiversity assessment, but cannot fully substitute in-depth taxonomic studies.