In the last few months, various government and non-governmental organisations in Andhra Pradesh, Odisha, and Punjab have released mosquitofish into local water bodies to address a mosquito menace that locals have complained about. In fact, officials in Visakhapatnam are set to release an additional six lakh mosquitofish after having released some 20 lakh a few months ago.
The world’s climate and habitats have changed noticeably in the last century, accelerating the spread of mosquito-borne diseases. Today, these diseases prevail in more than 150 countries worldwide, affecting more than 500 million people. In India alone, around 40 million individuals contract mosquito-borne diseases every year, and mosquito-borne illnesses have remained a persistent public health concern for many decades.
What is mosquitofish?
In this milieu, the biological control of mosquitoes assumes importance. In the 1960s, such approaches – including introducing mosquitofish in freshwater ecosystems to feed on mosquito larvae – became prominent as alternatives to chemical solutions like pesticides, which were found to have dire adverse effects on both human health and the ecosystem. The uptake of these alternatives increased in the 1980s and 1990s.
Many of them were considered to be environmentally friendly and sustainable. Among mosquito predators were two species of mosquitofish, Gambusia affinis and Gambusia holbrooki. In countries with governments that had approved this strategy, the authorities released them into freshwater ecosystems.
What they didn’t plan for, however, was that the fish began to proliferate here, with their populations eventually spreading far beyond their original habitats.
These species of mosquitofish originated in the U.S. but today have become global inhabitants. They are notorious for their detrimental ecological impact, including displacing and preying on native fauna, leading to the extinction of native fish, amphibians, and various freshwater communities. As such, Gambusia stands out as some of the most widely dispersed freshwater fish, aided by their robust adaptability and high tolerance for fluctuating environmental conditions.
Is mosquitofish ‘used’ in India?
The Indian Council of Medical Research (ICMR), India’s nodal medical research organisation, plays a significant role in mosquito management in the country – particularly in the context of controlling mosquito-borne diseases and conducting research to develop effective strategies.
In 1928, Gambusia was first introduced in India during British rule. Later, various governmental organisations, such as the ICMR, the National Institute of Malaria Research (NIMR), local municipal corporations, the Fisheries Department, and the Health Department, alongside other private organisations in India, took over as part of their efforts to combat malaria.
The idea of this scheme was that the newly introduced species would prey on or compete with mosquito larvae, reducing the latter’s population. The government also entrusted several municipal corporations, district administrations (and their health departments), fisheries departments, tribal development agencies, local aquaculturists, and the general public with introducing these fish across India.
Today, as in the American story, Gambusia, has become widespread in India as well, establishing self-sustaining populations in various habitats around the country.
The strategy was well-intentioned but it backfired, leading to severe ecological and environmental problems.
What effects has mosquitofish had?
The authors recently investigated the diversity of haplotypes and genotypes within Gambusia species in India. (Haplotypes are DNA variants likely to be inherited together; the genotype is an organism’s entire genetic material.) Our efforts revealed the widespread distribution of G. holbrooki and, to a lesser extent, G. affinis, the latter especially so in Northeast India.
Wildlife biologists and conservations consider mosquitofish to be among the hundred most detrimental invasive alien species. Aside from their resilience, these fish also have voracious feeding habits and have demonstrated aggressive behaviour in habitats to which they are introduced. India’s Gambusia story thus underscores the importance of careful consideration, research, and monitoring when using biological control methods to manage pest species.
Studies conducted in other countries have consistently revealed the harmful consequences of the presence of Gambusia in water bodies. For example, in Australia, introduced mosquitofish have led to the local extinction of the red-finned blue-eye (Scaturiginichthys vermeilipinnis), an endemic fish species. They have also been observed preying on the eggs and larvae of native fish and frogs. A study from New Zealand highlighted the threat posed by Gambusia to their native aquatic biodiversity. In India, some reports have indicated a decline in Microhyla tadpoles following the introduction of Gambusia.
For these reasons, the World Health Organisation stopped recommending Gambusia as a mosquito control agent in 1982. In 2018, the National Biodiversity Authority of the Government of India also designated G. affinis and G. holbrooki as invasive alien species. But both government and non-governmental organisations in India have continued to introduce these species for mosquito-control.
How can mosquitofish be controlled?
At this time, more stringent enforcement measures are crucial to prevent the species from continuing to be introduced to freshwater ecosystems and to manage the consequences of past introductions. Both also include the task of safeguarding our indigenous aquatic biodiversity and the well-being of native species.
Put differently, the problem today is both wolf at the door and termites at the base, and the optimal solution needs practitioners to tackle the problem from multiple angles. The first has to do with the National Centre for Vector Borne Diseases Control (NCVBDC) – of the Ministry of Health & Family Welfare – displaying a recommendation on its website for the use of Gambusia and Poecilia (guppy) fishes to manage mosquitoes. This recommendation must be removed.
Second, for effective mosquito control, alternatives to Gambusia should come from local solutions. Experts have suggested a collaboration between mosquito biologists/entomologists, invasion ecologists, and fish taxonomists, with a focus on river basins. Together, they can compile lists of native fish species in each basin that are capable of controlling mosquito larvae. Then, based on these lists, authorities can release the relevant species into the natural environment, sidestepping the risk of ecological repercussions posed by invasive alien species.
The authors are with the Ashoka Trust for Research in Ecology and the Environment, Bengaluru.
- India’s Gambusia story thus underscores the importance of careful consideration, research, and monitoring when using biological control methods to manage pest species.
- Today, as in the American story, Gambusia, has become widespread in India as well, establishing self-sustaining populations in various habitats around the country.
- The authors recently investigated the diversity of haplotypes and genotypes within Gambusia species in India.
