Spatial and temporal distribution of fish assemblages and its relationship with environmental factors in Lake Gehu

In order to understand the status and dynamics of fish community in Gehu Lake, the fishes at 16 stations in Lake Gehu were seasonally sampled using multi-mesh gillnets and traps from August, 2017 to May, 2018. Meanwhile, water temperature (WT), water depth (WD), transparency (SD), pH, chlorophyll a (Chl.a), total nitrogen (TN), total phosphorus (TP) were measured. Using these data, fish community structural characteristics, the spatial and temporal distribution pattern and its relationship with environmental factors were analyzed. A total of thirty-six fish species, belonging to 4 orders and 8 families, were collected from Lake Gehu. According to index of relative importance (IRI), Japanese grenadier anchovy (Coilia nasus) was the predominant species, silver carp (Hypophthalmichthys molitrix) and crucian carp (Carassius auratus) were the common species. Sedentary fishes (83.3%) predominated in species number among the three ecological groups and omnivorous fishes (47.2%) prevailed among the five feeding functional groups. The fish species composition in Lake Gehu did not differ monthly and spatially. The Two-Way analysis of variance (ANOVA) showed that number per catch effort (NPUE), richness index (R), Shannon-Wiener's diversity index (H´) and evenness index (J) significantly differed but biomass per catch effort (BPUE) did not differ monthly, and all the five structural features except R did not significantly differ between lake areas. Redundancy analysis revealed that WT and TP were the key factors influencing the spatial and temporal distribution of fish species of Lake Gehu. The results suggested that since 1950s the fish diversity has declined markedly and the species and product composition have changed greatly, which is speculated to be responsible for sharp degradation of macrophyte vegetation, overfishing, disconnection between lake and river, and breeding and enhancement.