Abstract
Between June 22 and October 18, 2010, 300 water systems on Okinawa Island covering a length of 340km were explored in order to record the distribution of 31 taxa of alien aquatic organisms and 41 taxa of native fish. They were confirmed mainly by visual observation while walking up the river on foot. The alien aquatic organisms were distributed mainly in the southern part of the island, although a few were seen in the northeastern part of the island. The tilapia (Oreochromis spp.), guppy, and carp were found in 141, 120, and 54 water systems, respectively. The sailfin catfish, redbelly tilapia, and red-eared slider turtle were distributed mostly in the southern part of the island, which has a high human population density. Ornamental fish such as the danio, platy, and small snakehead were found only in the northern part of the island, which has a low human population density. Endangered species and native fish were found mainly in the northern and central-western parts of the island. The swordtail is an alien fish that has an extensive distribution in the northern part of the island, and it is feared that it might influence some endangered species.
