Abstract
To understand the success of the invasions of non-native fish, it is important to identify feeding characteristics. The western mosquitofish Gambusia affinis were collected from February to December 2020 (excluding April and May) at Mizumoto Park in Tokyo, and the stomach contents of 180 specimens were investigated. A relative importance index (%MI) was calculated from the frequency of occurrence (%F) and weight composition (%W) for each food item ingested by the western mosquitofish. Food groups detected in the digestive tracts of the western mosquitofish were insects (mostly adult terrestrial insects), copepods, arachnids, and plants (mostly filamentous algae). Insects showed the highest %MI (98.3 %) throughout the study period, with a %MI above 90 % during summer and autumn. This feeding strategy of the species was supported by low niche breadth value. It is suggested that the western mosquitofish affects the feeding of native species in the study area by predominantly preying on insects, which are also important prey for many native species.
https://ror.org/025vmw012 
