The Western Mosquitofish, Gambusia affinis, is the most widely distributed fish in the world and likely the single biggest mosquito predator. Undoubtedly, this diminutive fish, no larger than a few inches, has saved more human and animal lives from mosquito-transmitted diseases than any other organism — doctors included. For this reason, the mosquitofish is humanity’s not-so-secret, but often overlooked weapon.
Native to the Mississippi River Valley, the mosquitofish has an upturned mouth and upward-facing eyes allowing it to scan the surface of the water where its prey suspend themselves from their air siphons. Another predatory advantage is that mosquitofish are viviparous — bearing live young instead of egg-laying. This allows mosquitofish to quickly invade new aquatic habitat and expand its population as rain expands its footprint. Its mosquito prey are often specialists at being the first organisms to infiltrate ephemeral aquatic habitat. When these newly wetted habitats begin to connect with others including those that harbor mosquitofish, mosquito larvae’s days or hours are likely numbered. It then becomes a race for the mosquito to emerge as a flying adult before the hungry mosquitofish consume all of the immature mosquitoes in the habitat.
Mosquitofish cannot survive very long outside of water and cannot survive in water with low dissolved oxygen (DO). These two requirements limit this weapon in the fight against the southern house mosquito. In natural conditions, shallow water habitats, such as those found in roadside ditches, characteristically have low dissolved oxygen levels made worse by extreme heat and drought which further limits the capacity of water to carry oxygen. With the addition of nutrients from partially treated OWTS discharges, mosquitofish survivorship is even more limited. The addition of human sewage tips the balance in favor of the southern house mosquito and away from its primary predator. As a rule, more is needed to promote healthy aquatic environments, which in turn provides tools to naturally regulate mosquito vectors. St. Tammany Parish Mosquito Abatement breeds mosquitofish and distributes them to the public upon request.