Hawaii’s 1905 mosquitofish import now linked to native species decline

Introduced to Hawaii in 1905 to control disease-carrying mosquitoes, the eastern mosquitofish (Gambusia affinis) has caused major declines in native aquatic insects, including several threatened species of Hawaiian damselflies. Conservation reports from the United States Fish and Wildlife Service (USFWS) show that the small, non-native fish has had a serious impact on Hawaii's freshwater ecosystems because of its aggressive and flexible feeding habits. The fish was originally brought from the southeastern United States during a period of agricultural expansion. It was then widely released into streams, drainage ditches and taro fields. Instead of eating only mosquito larvae, however, mosquitofish began feeding on many types of native aquatic animals. This changed local food webs and reduced populations of native species.Predation causes major declines in native DamselfliesUSFWS assessments of Hawaii's native damselflies (Megalagrion species) identify predation by introduced fish as one of the major causes of population decline.