Biological Control Measures in Malaria & Filaria Control Programmes

Biological control methods play a very important role in mosquito control activities. Two larva-eating fish are used

1. Gambusia affinis (mosquito fish)
2. Poecilia Reticulata (guppy or rainbow fish)

These two types of fish are known as larva-eating fish.

• These fish eat more larvae than adult mosquitoes.
• They survive easily in freshwater sources and are highly useful.
• Before releasing these fish into water collections, it is necessary to carefully estimate the number of eggs that will be laid there by mosquitoes.
• Fish can reduce mosquito breeding significantly in both malaria and filaria endemic areas.

1) Gambusia affinis (Mosquito fish)

• In 1928, Dr. B.A. Rao imported these fish from Italy and established a large-scale fish production center in the state of Mysore.
• Gambusia affinis is commonly known as the western mosquitofish.
• This fish is viviparous.
• Female fish are 6 to 621​ cm long, olive green in color, and suited for surface feeding.
• Male fish are 2 to 321​ cm long and smaller than females.
• Breeding Season: It varies in different provinces depending on the weather and environment, but it is usually from November to October.
• Females give birth at monthly intervals.
• They develop into mature fish within two months.
• One female gives birth to 250 to 300 young at a time.
• They eat all kinds of mosquito larvae.
• They especially prefer Anopheles larvae.

2) Poecilia Reticulata (Guppy fish)

• In 1910, India used it to reduce mosquito density under the malaria control program.
• In 1967, it was found in large quantities in the ‘Nag River’ in Nagpur, Maharashtra state, and since then it has been widely used everywhere in malaria and filaria control programs.
• The National Institute of Communicable Diseases, Delhi, started its work by bringing the above fish from Nagpur on a large scale as a larvae eater.
• Guppy fish are ovoviviparous, meaning embryos develop internally and young are released live and fully formed.
• Females can store sperm from multiple males, and brood sizes range from 20 to 40 fry every 4 to 6 weeks, enabling quick population growth.
• Guppy fish can survive even in dirty, polluted water.
• They cannot survive if the temperature drops below 10° to 11° Celsius.
• Similarly, it cannot tolerate temperatures above 42° Celsius.

Differences between Male and Female Guppy Fish

Male Fish	Female Fish
1) The stomach is flat.	1) The stomach is big.
2) It is small and thin in size.	2) The female is larger and more aggressive.
3) The pelvic fin is long and close to the anal fin.	3) The pelvic fins are small; the anal fin does not reach the pelvic fin.
4) The anal fin serves as the gonopodium (i.e., external genitalia).	4) There is no gonopodium.
5) Dorsal and pectoral fins are large and light.	5) Dorsal and pectoral fins are normal.
6) Colored spots are over the body.	6) The brown colour is everywhere.