GUIDELINES ON THE USE OF LARVIVOROUS FISH FOR
Fish have been widely used in public health, since as early as 1903. One of the most successful and widely used biological control agent against mosquito larvae is the top water minnow or mosquito fish Gambusia affinis. Fish other than Gambusia which has received the most attention as a mosquito control agent is Poecilia reticulata, the common guppy.
Fish have been extensively used for mosquito control in the urban malaria scheme under the National Anti Malaria Programme. In recent years some of the states have extended the use of fish Gambusia and Poecilia to rural areas in suitable breeding places as a supplementary measure for vector control. All the states have also been advised to upscale the use of fish as biological control method in rural areas. The following guidelines have been prepared to guide the states in the use of fish for vector control.
1.1 Advantages of use of Fish
1.2 Characteristics of Larvivorous Fish
2. SPECIES OF FISH
2.1 Gambusia affinis
Gambusia affinis has been in use in India since 1928. It is an exotic species and has been distributed throughout the warmer and some temperate parts of the world.
It is a very hardy fish and can adapt to wide variations in temperature as well as to chemical and organic content of the water but does not tolerate very high organic pollution. The optimum temperature for reproduction ranges from 240C to 340C but the fish can survive at freezing temperatures. The most suitable pH of water is between 6.5 and 9.9. Gambusia frequents areas especially suitable for the mosquito larvae. It lives and multiplies in ponds stocked with larger fish provided pond is shallow and has protective vegetation for refuge.
2.1.2 Size and Longevity
The maximum size attained by a male is 4.5 cm. and by a female 5.2 cm to 6.8 cm. Its life span is approximately 4+1 years.
2.1.3 Breeding Habit
The female matures in about 3 to 6 months. Each ovary contains approximately 120 eggs. Young ones are released in broods of 25–30 at a time. The young females have two gestations per season while the older females may have upto six generations per season. A season lasts about 30 days.
A single female may produce between 900 and 1200 off springs during its life span.
2.1.4 Breeding Season
Gambusia breeds throughout the year after maturity, especially in tropical conditions. In relatively colder climate such as is found in north and north-west India breeding period lasts from May to September and in warmer climate of southern India from April to November.
2.1.5 Larvivorous Efficiency
The larvivorous efficiency of Gambusia is due to following characters:
2.2 Poecilia reticulata (GUPPY)
Like Gambusia, Guppy is also an exotic fish introduced in India in 1910. It is easy to care for, and it reproduces quickly and prolifically. It is now widely distributed in India and is an important larvivorous fish.
It is a very hardy fish and survives in all types of water bodies. It tolerates high degree of pollution with organic matter. The temperature range suitable for breeding is from 240C to 340C. It can survive in water with pH ranging from 6.5 to 9.0 However, it can not survive in cold water (often below 100C) and stock may need replenishment if the temperature fall below 100C.
2.2.2 Size and Longevity
The male is 3 cm long, whereas the female is upto 6 cm in length. The Guppy lives for 4 + 1 years.
2.2.3 Breeding Habitat
The guppy takes about 90 days to mature. Each ovary contains 100 to 160 eggs. The female gives birth to young ones in broods of 5 to 7 at a time. About 50 to 200 young ones are released by the female every four weeks.
2.2.4 Breeding Season
Reported to breed throughout the year at about four weeks interval after maturity. However breeding season will depend on climatic conditions. In warmer climate it may breed from April to November.
2.2.5 Larvivorous Efficiency
The larvivorous efficiency of Poecilia is due to following characters:
3. FISH HATCHERIES
The Hatchery for larvivorous fish can be established in:
3.1 The Natural water body
Criteria for selecting a water body for a fish hatchery are:
3.2 Special Hatchery
Following points may be kept in view, while constructing the special hatcheries for the rapid reproduction of the fish:
4. TRANSPORTATION OF FISH
4.1 Collection of fishes
4.2 Precaution during Transportation
5. RELEASE OF FISH
5.1 Precautions during release of fish:
6. WHERE TO USE FISH
o Whether fish have been introduced or not
o Whether the fish are surviving or not
o Identification of possible reasons, in case the introduced fish are not surviving.