The Department of Public Health has instructed all
districts in the State to take up biological methods such as introducing
larvivorous fishes to control mosquito breeding, especially the malaria
vector.

The fish are to be introduced in all unused
wells in rural and semi-urban areas besides in freshwater such as
stagnant ponds and slow-moving streams before the mosquito breeding
season in order to maximise its impact.

R. Damodharan, Deputy Director of Health Services, told
The Hindu
here on Monday that Coimbatore district had already begun rearing
Gambusia affinis
, a species that originated from the U.S. that can adapt to local water
conditions. Distribution of the fish began in the city on Sunday through
the primary health centres.

While indigenous
larvivorous species such as haplochilus and barbus were also available,
he said these species had low tolerance to changes in temperature and
oxygen levels.

Each well must have at least a dozen
fish, with the male to female ratio being in the ratio of 1:3 in order
to effectively control mosquito breeding. Care must be taken to ensure
chlorination was not done in the water bodies where the fish were being
introduced.