Changes of fish fauna and invasion of non-indigenous Japanese fishes in recent years in Lake Saiko and Shojiko, Yamanashi Prefecture

Abstract

We investigated fish fauna in the littoral areas of Lake Saiko and Shojiko, Yamanashi Prefecture, Central Japan and compared them with those in previous studies. Two species have newly appeared in each lake: Oncorhynchus masou masou (Salmonidae) and Pseudogobio esocinus esocinus (Cyprinidae) in Lake Saiko and two Gobiidae species, Tridentiger brevispinis and Gymnogobius urotaenia, in Lake Shojiko. Three of these fishes are non-indigenous Japanese fishes and may have been introduced unintentionally in recent years, whereas O. masou masou was stocked for fishing by fishery managers of Lake Saiko. In Lake Saiko, the fish species composition has greatly changed and a goby, Rhinogobius sp. OR, has been dominated by another goby, T. brevispinis, during the past decade. In Lake Shojiko, species composition and dominant species has not changed and a goby, R. sp. OR, was the dominant benthic fish in littoral areas. However, we found that T. brevispinis has also invaded Lake Shojiko recently and greatly increased in number during the study period. The results indicated that unintentional introduction of non-indigenous fish species may have frequently occurred with fish stocking in recent years.