Recently, both governmental and non-governmental entities in Andhra Pradesh, Odisha, and Punjab have introduced mosquitofish into local water bodies to address concerns raised by residents regarding a mosquito menace. Authorities in Visakhapatnam are preparing to release an additional six lakh mosquitofish, following the earlier release of around 20 lakh a few months ago.

The global climate and ecosystems have undergone significant changes in the past century, hastening the proliferation of diseases transmitted by mosquitoes. Presently, these diseases are prevalent in over 150 countries, impacting over 500 million individuals. In India alone, approximately 40 million people contract mosquito-borne diseases annually, making such illnesses a persistent and significant public health challenge for many decades.

• Mosquitofish, particularly species like Gambusia affinis and Gambusia holbrooki, play a pivotal role in biological mosquito control. Introduced as an alternative solution in the 1960s, these fish were intended to thrive in freshwater ecosystems, feeding on mosquito larvae. This method gained popularity as an environmentally friendly substitute for chemical pesticides, known for their adverse effects on human health and the ecosystem.
• During the 1980s and 1990s, the adoption of biological control measures, such as deploying mosquitofish, saw a significant increase. These approaches were deemed sustainable and gained approval as effective means to address mosquito-related issues without resorting to harmful chemicals.
• Despite the initial intentions behind introducing mosquitofish, unforeseen challenges arose. In countries where governments endorsed this strategy, authorities released these fish into freshwater ecosystems. However, the unintended consequence was the unchecked proliferation of mosquitofish populations, extending far beyond their original habitats.
• Originally hailing from the U.S., these mosquitofish species transformed into global inhabitants. Notorious for their detrimental ecological impact, particularly species like Gambusia, they have been implicated in displacing and preying on native fauna. This, in turn, has contributed to the extinction of indigenous fish, amphibians, and various freshwater communities.
• Gambusia species, known for their adaptability and tolerance to fluctuating environmental conditions, have become some of the most widely dispersed freshwater fish globally. This notoriety stems from their unintended role in ecological disruptions, highlighting the importance of careful planning and monitoring when implementing biological control strategies to mitigate mosquito-related issues.

3. Utilization of Mosquitofish in India:

• Gambusia, a type of mosquitofish, was first introduced in India during British rule in 1928. The initiative aimed to address mosquito-related concerns and control mosquito-borne diseases, with the Indian Council of Medical Research (ICMR) at the forefront of these efforts.
• Various governmental organizations, including the ICMR, the National Institute of Malaria Research (NIMR), local municipal corporations, the Fisheries Department, and the Health Department, joined forces with private organizations in India. Together, they undertook mosquito management strategies, particularly focusing on combating malaria.
• The strategy involved introducing Gambusia into freshwater ecosystems, to have these fish prey on or compete with mosquito larvae, thereby reducing mosquito populations. The responsibility for implementing this scheme extended to municipal corporations, district administrations, health departments, fisheries departments, tribal development agencies, local aquaculturists, and the general public across India.

Unintended Consequences

• Similar to the American experience, Gambusia has proliferated in India, establishing self-sustaining populations in various habitats nationwide. The well-intentioned strategy, however, has led to unintended consequences, resulting in severe ecological and environmental problems.
• The initial intent to control mosquitoes and the introduction of Gambusia has backfired, causing ecological disruptions and environmental challenges. The widespread presence of these mosquitofish has raised concerns about their impact on native ecosystems, highlighting the need for careful consideration and monitoring in mosquito management strategies.

4. Ecological Impact of Mosquitofish

Recent research delved into the genetic diversity of Gambusia species in India, uncovering widespread distribution, particularly of G. holbrooki and, to a lesser extent, G. affinis, with a notable presence in Northeast India. Haplotypes and genotypes within these species were explored, shedding light on their genetic makeup.

Invasive Alien Species

• Wildlife biologists and conservationists globally recognize mosquitofish as one of the hundred most detrimental invasive alien species. Their resilience, voracious feeding habits, and aggressive behaviour in introduced habitats pose significant challenges to native ecosystems.
•  Studies from various countries, including Australia and New Zealand, showcase the harmful consequences of introduced mosquitofish. Local extinctions, predation on native species, and threats to aquatic biodiversity have been observed, emphasizing the need for caution in introducing such species.

Concerns in India

• Reports in India suggest a decline in Microhyla tadpoles following the introduction of Gambusia. Such indications raise concerns about the potential impact on indigenous aquatic biodiversity.
• Despite earlier recommendations, both the World Health Organization and the National Biodiversity Authority of the government of India have shifted their stance. In 1982, WHO stopped recommending Gambusia for mosquito control, and in 2018, G. affinis and G. holbrooki were designated as invasive alien species.

Ongoing Introduction Challenges

• Despite policy shifts, both governmental and non-governmental organizations in India persist in introducing mosquitofish for mosquito control. This raises questions about the enforcement of existing measures and the need for stricter regulations.
• Current circumstances demand more stringent enforcement measures to prevent further introductions of these species into freshwater ecosystems. Additionally, addressing the consequences of past introductions is crucial, emphasizing the protection of indigenous aquatic biodiversity and the well-being of native species.

5. Addressing the Mosquitofish Problem

The challenge at hand involves dealing with both immediate threats and long-term ecosystem health. To find the most effective solution, practitioners need to approach the problem from multiple angles, acknowledging the urgency of the "wolf at the door" and the subtler threat akin to "termites at the base."

Policy and Recommendations

The National Centre for Vector Borne Diseases Control (NCVBDC), under the Ministry of Health & Family Welfare, currently recommends the use of Gambusia and Poecilia (guppy) fishes for mosquito control. One key step towards a solution involves reevaluating and potentially revising these recommendations. Removing the endorsement of these species can be a crucial measure.

Localized Alternatives

• Effective mosquito control requires a shift towards localized solutions. Collaboration among mosquito biologists, entomologists, invasion ecologists, and fish taxonomists becomes imperative. This collaboration should focus on specific river basins to compile lists of native fish species capable of controlling mosquito larvae.
• Based on the compiled lists, authorities can strategically release native fish species into natural environments. This targeted approach aims to avoid the ecological repercussions associated with invasive alien species like Gambusia. By utilizing native species, the objective is to maintain ecological balance while effectively managing mosquito populations.

Holistic Approach

• A holistic solution involves integrating the expertise of various professionals, each contributing their knowledge to the broader goal of sustainable mosquito control.
• Mosquito biologists, entomologists, invasion ecologists, and fish taxonomists working in tandem can provide a comprehensive and ecologically sound approach to the complex issue at hand.
• Emphasizing a river basin-focused strategy ensures that interventions are tailored to the specific ecological conditions of each region. This approach minimizes the risk of unintended consequences and allows for a more nuanced and effective control of mosquito larvae.