10 million Gambusia fish released to combat malaria and dengue

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Context

State of Andhra Pradesh has recently released millions of Gambusia fish in many water bodies of state in a bid to control malaria, dengue and other mosquito-borne diseases.

Other Details

As per Union Ministry of Health and Family Welfare, Government of India (MoHFW), in 2022, there were approximately 6,391 dengue cases and 2,022 malaria cases in the state.
State of Andhra Pradesh saw a significant rise in the dengue and malaria cases.
- In last 6 months the state witnessed 2,339 dengue and 1,630 malaria cases.

Gambusia Fish

The fish belongs to family Poeciliidae and genus Gambusia.
This fish species shows a high breeding capacity for instance 900 and 1200 offspring could be produced during the lifespan of a single female Gambusia.
The fish is also known as mosquitofish or gambezi.
It is used as a biological agent for controlling mosquito larvae across the world.
G affinis has a sister species, Gambusia holbrooki (G holbrooki), also known as the eastern mosquito fish.

Features

These fishes are small in comparison to many freshwater fishes.
These can grow up to 7 cm (2.8 in) in length and can survive in diverse environments.
They are generally larvivorous however they also eat zooplankton, small insects and detritus material.
A full grown fish can eat as much as 300 mosquito larvae per day.

Habitat and distribution

It is considered one of the most widespread freshwater fish in the world.
They are commonly found in shallow waters which are protected from larger fishes.
As per MoHFW,
- Native region of Gambusia affinis (G affinis) - waters of the southeastern United States.
- Native range of the mosquitofish - southern parts of Illinois and Indiana.

Concerns

Concerns of Invasive species

A high breeding capacity, which is 900 and 1,200 offsprings per female fish, during its lifespan lead to an imbalanced high population of this species in aquatic ecosystems.
A season is 30 days long on an average and young ones are released in broods of 25-30 at a time.
- It may lead to more competition between other species for resources.
- They may prey upon native species thus harming the natural biodiversity in the state’s freshwater bodies.
- They are known to eat the eggs of competing fishes and frog tadpoles; Chase other fishes and restore to fin-nipping.
Gambusia is one of the 100 worst invasive alien species in the world according to International Union for Conservation of Nature (IUCN).
For example in Nainital India, mosquitofish was introduced in 1990 for controlling mosquito borne diseases. It had affected the ecosystem health of the Nainital lake.

Other Concerns

Introduction of this fish, however a good biological control method for source reduction, can only be a part of an integrated approach that involves various other methods like chemical spraying.
There are no conclusive studies about the effectiveness of Gambusia as a viable mosquito control.
G holbrooki may be ineffective for mosquito control, as mosquito larvae comprise a negligible part of its diet.
Not much monitoring and regulation of operations like Gambusia breeding, distribution and introductions and
No data availability for taking remedial measures.

History and Background for Disease control

For more than 100 years Gambusia has been used to control mosquito borne diseases across the globe, including India.
In India, this Mosquitofish, since 1928, has been part of various malaria control strategies and previously introduced in freshwater bodies across the country, like Andhra Pradesh, Chandigarh and Uttar Pradesh.
However few reports suggested that Gambusia’s predatory efficacy is reduced in running water streams, water bodies with high insecticide levels and waterbodies with thick vegetation.

More corrective measures

Reducing and frequently cleaning the number of mosquito breeding sources like puddles and open drainages. – kerosene oil could be used to hamper/destroy lava growth.
Vegetation can be cleared which host mosquitoes feed.
As per WHO this fish species should be used in man-made breeding habitats, like swimming pools and garden ponds, and not in natural environments.
Biologists and fish taxonomists should be encouraged to identify river basin-based lists of native fish species that can control mosquito larvae.