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Fresh water loving tiger prawns revive hope in shrimp farmers

The enterprising shrimp farmers of coastal Andhra Pradesh, who were adversely affected by the deadly 'white spot' disease in prawn and the subsequent Supreme Court order virtually banning shrimp culture in saline ponds near the sea, have learnt the lesson of survival from an unexpected source -- nature.

A majority of them are now growing the tiger prawn, which fetches huge foreign exchange, in fresh water as against the normal practice of its culture in brackish water the world over.

The clue was provided in 1977 when an unprecedented tidal wave, which claimed over 10,000 lives in the Diviseema region of Krishna district, moved shrimp from saline water ponds to fresh water ponds. The farmers found to their surprise that the eco-sensitive fish survived adapting itself to the new environs.

Almost 20 years later, scientists have been able to develop the tiger prawn under zero salinity conditions as against the optimum salinity of 15 to 25 parts per thousand required under normal culture.

For the farmers, hard pressed by the Supreme Court order in 1996 directing demolition of salt water ponds within the 500-metre of the high-tide line of the sea to preserve ecology, the new method became a virtual life-saver.

It involves bringing down the salinity to zero level for about 5-10 days after the seed has reached the post-larval stage. The seed then starts acclimatising to the fresh water conditions.

The tiger prawn (penaeus monodon) normally swims upstream to the fresh water for laying eggs and return. The larvae soon starts swimming downstream getting acclimatised by the time they reach saline water.

Scientists at the Union commerce ministry's Marine Products Export Development Authority in Vijayawada told this correspondent that the revolutionary technique was expected to usher in a new era of shrimp farming in the country.

Under the new method, shrimp farms can be set up in inland areas, thereby decongesting the already-chocked coastal zones and without affecting the environment.

According to available statistics, farmers in the Bhimavaram belt of West Godavari, Guntur, Nellore and East Godawari districts, who have cultivated the tiger prawn in about 6,000 hectares this year, expect a 2,755 tonne yield in the first crop itself. They had got the same yield in two crops last year.

The farmers now prefer to grow the tiger prawn in fresh water areas because this variety earns them Rs 450 to Rs 500 on 20 count. On the other hand, the scampi variety (macrobrachium rosenbergii), traditionally grown in freshwater environs, earned only half its price.

The latter has a restricted market while the former has demand the world over. The scampi held a sway on the farmers before the induction of tiger praws into the fresh water areas of the state.

India is a major shrimp exporting country in South Asia, after Thailand, Taiwan and Indonesia. The Supreme Court order on demolition of salt water ponds had affected shrimp culture in nine coastal states.

Out of about 170 hatcheries in the country, as many as 120 are located in Andhra Pradesh with each one having a capacity of 40 million seeds. The state also has a 135,000 hectare waterspread area compared to 1.2 million hectares all over the country.

A study of the area where the tiger prawn was grown under fresh water conditions has shown that there was no soil salinity and seepage unlike it happened in saline areas near the sea. The effluents were also minimal as the stocking density was less (30,000 to 50,000 per hectare) and the culture was ''modified extensive '' in nature.

UNI