The responses of stream fish to the gradient of conductivity: A case study from the Taizi River, China

Conductivity elevation produces osmotic stress to aquatic biota and then alters biological communities. The responses of stream fish to conductivity remain unclear and strategies for protection are poorly developed. We collected data of fish and conductivity from sixty-two sites of the Taizi River to evaluate the changes to the fish community and species along the gradient of conductivity. Our results found that conductivity elevation was related to the regional development of urban and farmland and the local degradation of habitat quality. The community metrics of abundance and F-IBI, but not species richness and diversity, showed a significant linear correlation with conductivity. Conductivity of the top three F-IBI grades (excellent, good and normal) was significantly lower than those of the other two F-IBI grades (poor and bad). The boundary conductivity between normal grade and poor grade was approximately equal to 500 mu S cm(-1). We found different probability patterns for different species along the conductivity gradient; one capture probability pattern showed decline trend along the conductivity gradient. Except for two dominating and widespread species and one tolerant species, the remaining fish species of the first pattern should be designated as protection objects. In order to protect fish community integrity and sensitive species, sustainable land use management on the catchment scale and habitat quality improvement on the local scale should be given more attention by catchment managers.