Western Mosquitofish, Gambusia affinis, is a member of the Poeciliidae family, which is a family comprised of live-bearing fish. They are one of the few freshwater fish to bear live young. Because of this, the young are able to feed like adults and increase their population quickly. They are a dull colored gray with small dark spots on their fins. Mosquitofish also have an upturned mouth and flattened head. They are rather small in size, females typically at 2-3 inches long, while males only 1-1.5 inches long (ODNR, 2017). They can be found in many ponds or slow flowing streams throughout Ohio, however they are not native to Ohio at all!
So, how did these little guys get here? Well, as their name suggests, they feed on mosquito larvae, as well as other small aquatic insect larvae. Mosquitofish are great eaters, consuming about 42-167% of their body weight every day! Because of this, they were thought to be a great pest control and alternative to insecticide for controlling mosquito populations (USGS, 2017). They were introduced to Ohio in 1947 in western Lucas County, but their region has since been expanded sporadically throughout the state (ODNR, 2017). As most non-native species introductions are, this was quite controversial.
Why may these teeny little fish be an issue? They may be small, but they are mighty! Also, as mentioned earlier, they can increase their population very fast. Mosquitofish have an extremely aggressive and predatory behavior. This makes them a threat to other small fish species through predation and competition. Mosquitofish populations may even displace native Ohio fish species, which is not good for the health of our streams. They have been found to be the reason for declines in several topminnow species, other fishes, invertebrates, and even amphibians throughout the continental United States. Recent introductions of Mosquitofish in New Zealand and the Hawaiian Islands reduced genetic diversity within the community (Purcell et al. 2012).
This invasive species causes more harm than good! It has been reported that Mosquitofish are not very effective in reducing mosquito populations. In fact, they may even benefit mosquitos by decreasing competition from zooplankton and reducing predation from other invertebrates (Blaustein and Karban 1990). Mosquitofish can also potentially cause algal blooms by feeding on an abundance of zooplankton grazers (Hurlbert et al. 1972).
Mosquitofish are only one example of a non-native species, including many plant species, introduced to Ohio to serve some purpose. It seems to be a game of chance whether the introduction causes harm or good. It is clear that research and much consideration should be taken before altering the environment in such a drastic way.
Check out other invasive Ohio fishes here (under the heading ‘Invasive Fish’): http://wildlife.ohiodnr.gov/species-and-habitats/species-guide-index/fish
Bibliography:
Blaustein, L., and R. Karban. 1990. Indirect effects of the mosquitofish Gambusia affinis on the mosquito Culex tarsalis. Limnology and Oceanography 35(3):767-771
Hurlbert, S.H., J. Zedler, and D. Fairbanks. 1972. Ecosystem alteration by mosquitofish (Gambusia affinis) predation. Science 175:639-641.
Ohio Department of Natural Resources (ODNR). 2017. Western Mosquitofish. Retrieved from: http://wildlife.ohiodnr.gov/species-and-habitats/species-guide-index/fish/mosquitofish
Purcell, K.M., N. Ling, and C.A. Stockwell. 2012. Evaluation of the introduction history and genetic diversity of a serially introduced fish population in New Zealand. Biological Invasions 14:2057-2065.
United States Geological Survey (USGS). 2017. Gambusia affinis. Retrieved from: https://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=846
Photo credits:
- https://media1.britannica.com/eb-media/17/162017-004-55658173.jpg
- http://wildlife.ohiodnr.gov/species-and-habitats/species-guide-index/fish/mosquitofish