Temporal and Size-Related Trends in Food Habits of Introduced Western Mosquitofish and Native Topminnows

Abstract

Western mosquitofish (Gambusia affinis) are stocked in Indiana waters for the biological control of mosquitoes. However, this species has the potential to negatively impact native fishes. We examined the food habits and diet overlap of adult western mosquitofish, northern starhead topminnow (Fundulus dispar), northern studfish (F. catenatus), blackstripe topminnow (F. notatus), and banded killifish (F. diaphanus) in Indiana from April through October 2005 to evaluate trophic resource use by month and body length. Food habits for each species were similar, with the largest percentage of the diet composed of zooplankton (Cladocera) and non-culicid diptera (Chironomidae and Ceratopagonidae). There was no trend in the percentage of culicids (mosquito larvae) consumed by species, regardless of month and body length (range, 0–27%). Diet overlap index values between western mosquitofish and the topminnow species were high but there was no clear trend, regardless of month (range, 0.25–0.87) or body length category (range, 0.49–0.83). Because food habits for the fishes examined in this study were similar and there exists the high potential for negative behavioral impacts by western mosquitofish, we do not recommend stocking this species into Indiana waters that contain native topminnows.