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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. diaphamis) 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. [ABSTRACT FROM AUTHOR]

The stocking of western mosquitofish (Gambusia affinis) to control mosquitos has been shown to negatively impact native fishes, especially species with similar ecological requirements such as topminnows. As a result, using fish species (e.g., blackstripe topminnow; Fundulus notatiis) that are native and rarely exhibit aggressive behaviors toward ecological equivalents may serve as a non-intrusive means of mosquito control. In this study, a series of laboratory microcosm experiments were used to examine intra- and interspecific agonistic behavioral interactions (e.g., chases and nips) between blackstripe topminnow and northern starhead topminnow (Fundulus dispar), northern studfish (F. catenatus), and banded killifish (F. diaphanus) at three different fish density combinations and in the presence or absence of vegetation. Few agonistic behaviors were exhibited toward conspecifics, but interspecific chasing and nipping did occur, albeit it at low levels, in the presence of blackstripe topminnow. The number of these interspecific chases and nips was not influenced by vegetation or topminnow species density. Fin damage incurred by topminnows was minimal, regardless if tanks contained only individuals of the same species or another species (blackstripe topminnow). Three percent of blackstripe topminnows had damage to their caudal fins that was intraspecific in nature, but there was no fin damage for the other three topminnow species. Based on these results, we suggest that blackstripe topminnow be considered as an alternative to western mosquitofish for mosquito control in drainages for which it is a native species. [ABSTRACT FROM AUTHOR]

Western mosquitofish, stocked frequently throughout Indiana, are highly aggressive and often negatively impact native fishes that occupy a similar ecological niche. Because northern starhead topminnows are the most vulnerable of the Indiana topminnows to western mosquitofish aggression, we conducted a 110-day outdoor mesocosm experiment from June through October 2006 to examine changes in abundance, biomass, and wet weight per individual fish at different topminnow and mosquitofish densities. Control mesocosms (three replicates per treatment) contained either 30 northern starhead topminnows or 30 western mosquitofish, while experimental treatments (three replicates per treatment) contained both species at one of the following density levels: (1)20 topminnows and 10 mosquitofish; (2) 15 individuals of each species; and (3) 10 topminnows and 20 mosquitofish. During the experiment, western mosquitofish exhibited successful reproduction while northern starhead topminnows declined in mean abundance, biomass, and wet weight per individual, indicating that the presence of western mosquitofish had a negative impact on topminnows. However, northern starhead topminnows did not have any negative impact on western mosquitofish. Based on these results, we do not recommend stocking western mosquitofish into Indiana waterways. [ABSTRACT FROM AUTHOR]