Fish diversity reflects biological invasions and environmental change in highly urbanized Chinese river networks

Urban rivers, which provide essential ecosystem services and support significant biodiversity, are experiencing rapid species loss due to various anthropogenic stressors, yet they have received relatively limited research attention. In this study, we analyzed fish diversity and its relationship with environmental factors in northern Shenzhen, the third most populous city in China. A total of 4115 fish specimens were collected, representing 50 species (36 native species and 14 non-native species), belonging to 22 families and five orders. Non-native fish species accounted for 28.0% of the total number of species, 57.3% of the total abundance, and 85.4% of the total biomass. Sørensen dissimilarity in the Guanlan River and Gongming Lake was lower than those in other studied areas, indicating a trend toward biotic homogenization. The fish community structure exhibited significant spatial variation across the northern Shenzhen river networks and was correlated with environmental factors, mainly ammonia nitrogen and total nitrogen. This study provides a comprehensive assessment of northern Shenzhen fish diversity, providing information that can guide future conservation and restoration actions, including the control or even eradication of some non-native fish species.