Longitudinal Patterns in Fish Assemblages after Long-Term Ecological Rehabilitation in the Taizi River, Northeastern China

Fish assemblages inhabiting the Taizi River basin have been severely degraded by anthropogenic disturbances, which weaken the basin's ecological function and limited revitalization of the northeast industrial base. Long-term ecological rehabilitation has been conducted to restore the fish fauna and improve habitat conditions. To explore fish distribution patterns and key factors after this ecological rehabilitation, a comprehensive and detailed survey of fish fauna was conducted twice in 2021 at 33 sampling sites in the Taizi River. A total of 50 fish species from 13 families were collected, and the dominant species were P. lagowskii, Z. platypus, C. auratus and P. parva. Compared to results reported over the last decade, the increasing trend in fish richness and the change in the longitudinal fish organization were detected. The abundance variation for P. lagowskii, Z. platypus, C. auratus, P. parva, R. ocellatus and H. leucisculus along the upstream to downstream axis contributed most to the fish distribution pattern. Species replacement and addition might have jointly caused the longitudinal changes in the fish fauna, but species replacement was the main underlying mechanism. The canonical correspondence analysis (CCA) results show that the fish structure pattern was mainly shaped by cultivated land coverage and urban land coverage. Our study provides reference sites for future fish-based bioassessment and implications for region-specific management in the Taizi River.