Food web structure composed of alien fishes in Okinawa Island, Japan: a stable isotope approach.

The freshwater fish community in subtropical Okinawa Island, Japan, was originally poor and is now mainly composed of alien fishes. Fishes caught in an impoundment of the Hija River and the Haebaru Reservoir were measured for carbon and nitrogen stable isotope ratios to estimate the trophic niches of the alien fishes. Fish fauna of the two habitats were mainly composed of alien fishes originating from Africa and South and Central America. Isotope ratios suggested that alien fishes included two trophic types - food-partitioning types like armored catfish, Poeciliidae, and redbelly tilapia that each use a unique trophic niche, and food-overlapping types like cichlids that all have similar trophic niches.