2.2 Field survey
A total of 106 sites (53 impoundments and 53 free-flowing segments) were sampled across the Wannan Mountains only in the wet season (August 2015). Meanwhile, the highland streams discharges of this region are characterized by flashy pulses with high-flow conditions during the wet season (Yan et al., 2013). Following the standardized methods (i.e., stream length and sampling time) of Li et al. (2021), stream fish assemblages were sampled at each site using a backpack electrofishing unit (CWB-2000 P, China; 12V import and 250V export) by wading in two passes. Based on Nelson’s (2006) classification method, all fishes were identified in the field to species and counted. At least 20 adult specimens of each species were used to measure the traits, and all adult specimens were measured when the species contained less than 20 adult individuals. Whenever possible, only a fraction of abundance-dominant species returned to the sampling sites if alive and the remaining species were retained for further laboratory identification and measurement. Fish handling procedures were performed following bioethical protocols established by the Anhui Normal University Animal Ethic Committee.
We characterized the local habitat conditions of each sampling site using seven habitat variables, including wetted width (m), water depth (m), current velocity (m/s), dissolved oxygen (mg/L), water temperature (°C), substrate coarseness, and heterogeneity. The wetted width was measured along three equally spaced transects that ran across the surveyed stream channel. The water depth was measured at three equally spaced points along each transect. The current velocity was quantified at 60% of the water depth at each point using FP111 (USA). Dissolved oxygen and water temperatures were measured using an YSI Professional Plus meter (USA). The substrate was quantified within each sample site and divided into 10 cross sections based on the size-class frequency method of Bain et al. (1985): particle size 0 = 0–0.059 mm, 1 = 0.06–1 mm, 2 = 2–15 mm, 3 = 16–63 mm, 4 = 64–256 mm, and 5 = >256 mm. The mean and standard deviation of the substrate values were used as indices of substrate coarseness and heterogeneity, respectively.