Non‐native freshwater fish species in the Yellow River Basin: origin, distribution and potential risk

Invasions of non-native fishes are recognized as a serious threat to freshwater biodiversity across the globe. Being the China’s second-largest river, the Yellow River has experienced severe invasion pressure of non-native fishes during recent decades. However, much less is known about species composition and distribution of non-native fishes in this river basin. Here, we investigated and summarized the literatures about non-native freshwater fish in the Yellow River Basin (YRB), to examine their taxonomic diversity, geographical origin, longitudinal distribution and potential risk. We found that 40 non-native fish species, belonging to 9 orders, 18 families and 35 genera, have invaded the YRB. Of which 19 exotic species came from other regions, while 21 translocated species were introduced into the upstream from midstream and downstream of the YRB. The aquaculture was the main vectors responsible for non-native fish introductions. An average of 8.24 non-native fish species was introduced and established per sub-region, accounting for 25.5 % of total fish species. The percentage of non-native species showed a significant unimodal model against average elevation, with the highest values (ca. 70 %) in upstream mainstream reaches and tributaries. Non-native species from historically absent or species-poor orders (Salmoniformes, Osmeriformes and Perciformes) were the most successful invaders. Furthermore, the species composition of non-native fishes changed markedly along the longitudinal gradient (i.e., from source region to downstream). The negative impacts of non-native fish introductions to native fish species, e.g., competition for resource, predation and hybridization were emerged in many introduce regions and could get worse in the future due to global warming and human activities. This study can help improve the management of non-native fish introductions and biodiversity conservation of native and endemic fish species in the YRB.