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Iran is one of the world's fish biodiversity hotspots. Most riverine fish species in this country are currently under threat by human activities. In addition to those threats, climate change is expected to alter rainfall and temperature regimes, imposing further limitations, particularly to endemic fishes. Therefore, understanding how these species respond to climate change is an important issue in the conservation of Iranian freshwater biodiversity. This study aimed to predict the potential distribution of 16 endemic fish species under two climate change scenarios (i.e., RCP 4.5 and RCP 8.5) in river habitats of Iran in the 2050s and the 2080s. The analysis is conducted using the MaxEnt model. Seven environmental variables were used for modelling: maximum width, elevation, river slope, the basins occupied by the target species, average annual precipitation, annual mean temperature, and the temperature difference between the coldest and hottest months of the year . The validation of the model for each species showed that AUC (area under the ROC curve) scores range from 0.87 to 0.99. Under optimistic (RCP 4.5) and pessimistic (RCP 8.5) scenarios in the 2050s and the 2080s, species will face four different outcomes to their habitat range: reduction (three species), expansion (five species), reduction and expansion (seven species) and no change (one species). It is concluded that most species that are unique in their geographical area will face serious challenges from climate change. Delineating species range changes under climate change scenarios can help prioritise conservation measures for these valuable species. Considering our results, the translocation of species to new locations also should be investigated.

The future changes in the spatial distribution and richness of 131 riverine fish species were investigated at 1481 sites in Iran under optimistic and pessimistic climate change scenarios of 2050 and 2080. The maximum entropy model was used to predict species’ potential distribution under current and future climate conditions. The hydrologic unit (HU) occupancy of the target species through the use of nine environmental variables was modeled. The most important variable determining fish occupancy was HU location, followed by elevation, climate variables, and slope. Thirty-seven species decrease potential habitat occupancy in all future scenarios. The southern Caspian HU faces the highest future species reductions. The southern Caspian HU, western Zagros, and northwestern Iran will be at higher risk for species richness reduction. Managers could use these results to plan conservational strategies to ease the movement and dispersal of species, especially those that are at risk of extinction or invasion.