Disentangling drivers of native fish loss and non-native fish dominance in highly urbanized rivers of Shenzhen, China

Rapid urban expansion impacts freshwater ecosystems globally and accelerates invasion of non-native fishes while related ecological processes and mechanisms are still not clear. The processes shaping the distribution and composition of native and non-native fish assemblages were explored through a four-year study in highly urbanized rivers in Shenzhen in southern China. We collected data for fish abundance in local assemblages and used the Joint Species Distribution Model (JSDM) to investigate key driving factors influencing fish distributions. We found that water quality was the main factor affecting the distribution and abundance of native fishes, whereas spatial random effects and land use explained more than half of the variance for non-native fishes. We also analyzed species distribution and abundance in relation to phylogeny and functional traits associated with morphology, life history and physiology. Greater levels of urbanization were associated with larger body length, longevity, fecundity and pectoral fin size. Phylogenetic niche conservatism was a dominant pattern in the dataset. Positive correlations among non-native fish species suggests that these urban rivers may be undergoing an “invasional meltdown”. Overall, our findings demonstrate that urban rivers can act as environmental filters that exclude sensitive native fish while facilitating the establishment and dominance of tolerant non-native species. These insights point to practical interventions: improving water quality, managing land use and limiting dispersal pathways may help mitigate native fish loss and reduce non-native dominance in urban river systems.