Distribution and COI clade composition of Phoxinus populations in the Sieg basin based on specimens collected in the framework of this study. The red rectangle in the inset shows the location of the Sieg in Germany. Circles represent fished sections: black empty ones with no Phoxinus caught, green empty ones with Phoxinus caught but not barcoded, filled circles for sections with Phoxinus caught and successfully barcoded. The size of the circles is relative to the number of barcoded specimens, the colour denotes the COI-clade identity according to Palandačić et al. (2020). Grey continuous lines indicate the designated Sieg basin zonation into mountainous and foothill region, based on major basin borders (confluences, weirs and artificial waterfalls), administrative districts and geographical regions. Dashed grey lines indicate the sub-region basin divide between Sieg and Agger. All streams discussed in the text are labelled in the figure. The neotype locality of P. phoxinus is indicated by a black target symbol. A single record of clade 11 is indicated by a black arrow.