In a bid to combat mosquito-borne diseases like malaria and dengue, the government of Andhra Pradesh has recently released approximately 10 million Gambusia fish into the state’s water bodies. These fish, commonly known as mosquitofish, have long been employed as a biological solution to control mosquito larvae proliferation.
However, the release of these invasive alien species has triggered concerns about the potential harm they might inflict on the indigenous aquatic ecosystems of the state.
According to data from the Union Ministry of Health and Family Welfare, Government of India (MoHFW), Andhra Pradesh reported around 6,391 dengue cases and 2,022 malaria cases in 2022. Disturbingly, local news reports indicate a significant rise in cases over the past six months, with 2,339 dengue cases and 1,630 malaria cases registered in the state.
Gambusia affinis (G. affinis), originally hailing from the southeastern United States, is a voracious predator capable of consuming about 100 to 300 mosquito larvae per day, as per MoHFW.
The use of Gambusia in mosquito-control strategies has been practiced worldwide for over a century, including in India. Its sister species, Gambusia holbrooki (G. holbrooki), also known as the eastern mosquito fish, has been an integral part of malaria control initiatives in India since 1928, including the Urban Malaria Scheme.
While mosquitofish are generally considered a valuable biological control method for curbing mosquito breeding, experts emphasize that they should be just one component of a comprehensive approach. This approach must include other methods like chemical spraying and, most importantly, source reduction, according to Desham PR, a public health practitioner in Telangana.
“Reducing the number of mosquito breeding sources like puddles and open drainages, and clearing vegetation that mosquitoes feed on must be prioritized over releasing fish into water bodies,” she stressed.
Notably, the effectiveness of Gambusia as a viable mosquito control method remains inconclusive. While some studies have shown a reduction in malaria cases where the fish were introduced, others have reported an increased mosquito larvae population because Gambusia preyed on other predators that consumed mosquito larvae. Additionally, the predatory efficacy of Gambusia declined when introduced in running water streams, water bodies with high insecticide levels, and water bodies with dense vegetation.
One of the most concerning aspects of Gambusia is its high breeding capacity. A single female can produce between 900 and 1,200 offspring during its lifetime, as per MoHFW. With up to six generations per season, this adaptability has allowed Gambusia to thrive on six of the seven continents, leading the International Union for Conservation of Nature to categorize it as one of the 100 worst invasive alien species globally.
Several countries, including India, have listed Gambusia as an invasive species. Nevertheless, the fish continues to play a prominent role in the country’s malaria control programs, with releases into freshwater bodies occurring in various regions such as Andhra Pradesh, Chandigarh, and Uttar Pradesh.
Known for its competitive and predatory behavior, Gambusia can outcompete and prey upon native species, leading to concerns over its potential impact on local ecosystems. Observations include the consumption of competing fishes’ eggs and frog tadpoles, as well as aggressive behaviors such as chasing other fishes and fin-nipping.