In 1905, New Jersey received mosquitofish from North Carolina to fight mosquitoes; the species are now considered harmful to resident aquatic wildlife

Anyone who has ever stayed awake listening to a mosquito buzz knows the urge to fight back. New Jersey did just that back in 1905, but in an unusual way. The US Geological Survey's Nonindigenous Aquatic Species database says that a small fish called Gambusia, reportedly from North Carolina, was released into New Jersey waters that year to control mosquitoes. The plan seemed smart, simple, and cheap. But over time, the fish ended up becoming a tricky guest. Now they are seen as a threat to wildlife already living in local waters.Why the tiny fish looked like a big solutionMosquitofish got their name because they feed on mosquito larvae, the wriggling young ones that develop in water. This made them appear as an ideal natural pest controller. The USGS explains that people often stocked them with little care in temperate and tropical regions around the world. It adds that groups like the former US Public Health Service released them in the decades that followed. They considered this fish to be a low-cost solution for malaria. The introduction in New Jersey was part of the earliest introductions in the United States, which took place during the early 1900s. In the same year, about 150 fish from Texas were also released in Hawaii. The goal there was to test how well they eat mosquito larvae.Did the fish really work?The USGS notes that critical reviews of research from around the world don't support the view that mosquitofish are especially good at cutting mosquito numbers or mosquito-borne diseases. Neither are they gentle neighbours. The database describes them as aggressive fish that frequently attack other species. They tear off fins and often kill other fish. They eat the eggs, larvae, and young of other fish and also prey on smaller species of adult fish. In some waters, they can even backfire. If they eat the small animals that usually prey on mosquito larvae, instead of falling, mosquito numbers may rise.What this means for local wildlifeNow, New Jersey Fish and Wildlife has adopted a clear view. Its freshwater fish guide classifies the western mosquitofish as non-native, explaining that the fish was cultivated and stocked for mosquito control purposes. The species is considered harmful to populations of resident fish and amphibians. The fish should not be stocked in areas where they may affect native species. However, there is some inconsistency here. In the same guide, eastern mosquitofish is classified as native to the southernmost parts of the state. Moreover, it says that the two species may be difficult to tell apart. According to USGS, many of the early releases were poorly documented, so it is often uncertain what species was moved. One of the strongest pieces of evidence of harm comes from the American West. There, the agency says, the mosquitofish contributed to the decline or local loss of threatened or endangered species. In Arizona, introduced fish, including mosquitofish, are believed to play a part in the decline of the Chiricahua leopard frog.A lesson that still mattersThe 1905 release shows how a quick fix can end up casting a very long shadow. The fish didn't solve the mosquito problem. Instead, they also brought fresh worries for the creatures already living in the water. So, if you ever think of stocking a pond with fish to control mosquitoes, it might be a good idea to consult with local wildlife officials first. A small fish with a good reputation can still do big damage once they settle into a new home.You use AI every day. Now get your AI Quotient. Take the AIQ test.