Freshwater fishes in Lake Izunuma-Uchinuma basin, Japan: distribution patterns of native species and invasive species

Abstract

In Lake Izunuma-Uchinuma basin, freshwater fishes comprised 12 families with 36 species. Most belong to non-diadromous freshwater fishes including endemic species in eastern Japan such as Acheilognathus typus, A. melanogaster, Pseudorasbora pumila, and Pseudobagrus tokiensis. The basin consists of open water such as Lake Izunuma-Uchinuma and influent rivers, and closed waters such as irrigation ponds. In Lake Izunuma-Uchinuma and the influent rivers, the fish communities showed lower density of native fishes due to influence of non-native largemouth bass. In the irrigation ponds, the existence or nonexistence of largemouth bass affected to the fish communities. The ponds with largemouth bass had a degraded native fish community, whereas the ponds without largemouth bass had many native species. These native species included several rare species that had become extinct in Lake Izunuma-Uchinuma. These results indicated that irrigation ponds served a role as refugia for rare fishes when the influence of invasive species became widespread.