Climate-Driven Range Expansions in Freshwater Fishes: Taxonomic Consequences, Cryptic Invasions, and Phylogeographic Shifts

Abstract

Climate-driven redistribution of freshwater fishes is increasingly apparent, yet its taxonomic and evolutionary implications remain inadequately integrated into distributional assessments. This critical review connects thermal and hydrological niche change with river-network dispersal, taxonomic uncertainty, cryptic invasions and phylogeographic reorganization. Long-term records reveal asymmetric population responses near cooler and warmer range margins and frequent lags between changing climate and realized geographic movement. DNA barcodes and population genomics show why species-level maps can obscure independently structured lineages or genetically foreign introductions. The spread of rainbow trout ancestry into native cutthroat trout populations illustrates how climatic trends may accelerate introgressive hybridization against a background of historical stocking. We distinguish natural climate tracking, human-mediated introductions, previously overlooked occurrence and taxonomic reassignment, and propose an integrated evidence sequence combining repeated detection-corrected surveys, voucher-based taxonomy, eDNA, genomic source assignment, historical collections and network-aware models. Climate suitability must not be conflated with colonization, molecular detection with establishment, or hybridization with demonstrated adaptive benefit. A shift toward lineage-aware, temporally explicit assessments is necessary to conserve both species persistence and evolutionary diversity under rapid environmental change.