Data collected in a citizen scientist study uncover a new species record of Phoxinus minnow for Austria

Freshwaters are among the most vulnerable ecosystems, yet the scarcity of biodiversity assessments prevents the detection of changes incurred by neobiota. Minnows of the genus Phoxinus were long thought to be represented by a single species in Eurasia, the common minnow P. phoxinus, but the genus now includes more than 25 valid species. However, their distributions do not follow drainage boundaries, there are known cases of human translocations, and morphological species assignation is difficult due to intra- and interpopulation phenotypic diversity. Hence, the species were delimited and are now determined mostly using molecular methods. In Austria, recent studies have identified at least four different species of Phoxinus, three of which are considered native and one introduced. However, more data were needed; thus, extensive collecting and DNA barcoding of minnow populations was undertaken with the help of recreational fishers, school pupils, and field biologists. DNA barcodes of museum specimens and environmental DNA collected from water samples were also included. Altogether, the genetic lineage of 258 new Phoxinus specimens was determined. The results confirmed the distribution of P. marsilii in eastern Austria, P. lumaireul in southern Austria and P. csikii in central and western Austria. Additional populations of the introduced P. phoxinus were identified. Most importantly, a new species record for Austria, P. cf. morella, was discovered, yet it is unclear whether its distribution in Austria is natural. This study also confirmed the potential of citizen science for biodiversity monitoring, with the number of specimens analyzed increasing fourfold in just two years.