Distribution of A native, B exotic and C endemic fish species across six Basins in the Qilian Mountain Basin; codes are shown in Fig. 1. Vertical bars show the number of species occurring in each of the unique combinations of basin represented by the single point for a set of species unique to one basin and the connected points for a set of species co-occurring in multiple basins (e.g. A five native fish species occurred in the HHR, SLR and SYR, but in no other basins).