Emergent plant zones on the shores of temperate lakes and ponds function as an essential habitat for various fish species, although few studies have focused on spatial variations in fish fauna over a range of such habitat within a single river system. In order to promote a better understanding of conservation requirements for the fish habitat, the fish fauna of emergent plant zones was investigated by quantitative fyke-net sampling, with measurements of environmental properties, at 19 sites in seven lakes and three ponds in the lower Tone River system, eastern Japan in June and August 2017. A total of 27 and 34 species, including commercially important and threatened species, were collected in June and August, respectively. A cluster analysis based on species composition at each site in each month showed that the fish assemblage was divided into three groups: six medium and large-sized lakes, a small lake and pond on the floodplain, and ponds in the hilly areas. The differences in species composition among the groups were partly related to different elevation, impacts of downstream weirs, and occurrence of introduced piscivorous species. In addition, analyses of the relationships between fyke net catches of eight abundant fishes and environmental variables at each site in the medium and large lakes at lower elevation (< 5 m) in each month, using a generalized linear mixed model, indicated that wave height and mud content in sediments, as well as emergent vegetation size, were significant determinants of abundance of most species. Accordingly, deliberate conservation and rehabilitation of emergent plant zones, taking such essential information into consideration, should be included in future conservation plans for fish habitats in the Tone River system.
