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More rohu for the Bengali plate
- aqua trick to breed carp in winter

New Delhi, Oct. 16: Three species of freshwater fish dear to the Bengali palate may soon be bred throughout the year through an aquaculture trick that could help boost fish production.

The three Indian major carps — rohu, catla and mrigal — breed in nature only during the monsoon season, although they are grown in aquaculture ponds and sold throughout the year.

Now, scientists at the Central Institute of Freshwater Aquaculture, (CIFA) Bhubaneswar, have for the first time coaxed carps to breed during winter by exposing them to artificial light and warm temperatures, simulating longer and hotter days. The altered light and warmth trigger physiological changes in the fish that induce off-season breeding.

“Basically, we fool the carps into breeding even during winter,” said Ambekar Eknath, director of CIFA. “This will allow us to produce fish seed for aquaculture ponds throughout the year.”

Thousands of natural and artificial water bodies used across the country as ponds for aquaculture currently contribute nearly half of India’s inland fish production.

The CIFA scientists exposed laboratory-bred rohu, catla and mrigal to artificial light to simulate 15.5 hours of daylight and 8.5 hours of darkness over several weeks from October through December.

Under these conditions, the carps showed accelerated sexual maturation, and the mature females of rohu and catla produced similar quantity of eggs and spawns as they do just before the onset of monsoon, the CIFA researchers said, describing their findings in the journal Current Science.

Although the mrigal also bred, it had a lower quantity of eggs, showed poor fertilisation and hatching rates, and the number of spawn — newborn fish — was low.

“This photothermal manipulation of reproduction will increase the number of times fish can be bred in a year which, in turn, will help in producing more fish seed for stocking in aquaculture ponds,” said M.R. Raghunath, head of the peninsular aquaculture division of CIFA, Bangalore, who was not associated with the study. “The more the fish seed, the higher can be the production of fish.”

Eknath said similar manipulation of reproduction had earlier been achieved by scientists in other countries in aquarium fish as well as in striped bass and Atlantic cod. “This is the first time photothermal manipulation of reproduction has been shown in an important commercial carp of India,” he said.

The researchers believe the induced breeding four or five months before monsoon will give aquaculture farmers more time to allow fish to grow in water bodies and thus harvest fatter fish for sale.

However, aquaculture scientists caution that just extra fish seed may not always translate into higher production. Factors such as nutrition and water quality will also determine harvest size.

“We’re hoping this will mean more profits for farmers,” Eknath said. However, for any meaningful impact on India’s fish production, the breeding technology will need to be moved from the laboratory into commercial aquaculture ponds.

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