It takes seven months to produce 2,000kgs of pabda (Ompok) from a fish farm the size of a football pitch. How about getting the same results in half the time from an indoor space that is hardly the size of a penalty box?One fish farmer in Bangladesh has demonstrated that it can be done. He used the recirculating aquaculture system (RAS) for the first time in the country.

An alternative to outdoor open aquaculture, RAS is a series of culture tanks and filters where water is continuously recycled and monitored to keep a suitable habitat for fish round the year. To prevent the deterioration of water quality, the water is treated mechanically through the removal of particulate matter and biologically through the conversion of harmful accumulated chemicals into nontoxic ones.

“It's innovative. It's promising. We've installed the indoor fishery unit in November for research and demonstration purposes. Once entrepreneurs start taking interest in RAS, this will further revolutionise the fish sector in Bangladesh,” said Rezaul Karim, who heads the Centre for Technology Transfer and Innovation (CTTI) at BCSIR. With an annual production of nearly 1.8 million tonnes of cultured fish, Bangladesh is the world's fifth largest producer of inland aquaculture after China, Indonesia, India and Vietnam, the UN Food and Agriculture Organisation (FAO) stated in its State of World Fisheries and Aquaculture-2016 report.

RAS' main advantage is its high stock density. Compared to one to two kgs of fish being produced per cubic metre of water in an open pond, RAS has the stock density of 20 to 60kgs per cubic metre depending on fish species.

Rezaul explained how an ideal RAS functions. He said water is purified and recirculated in the fish tanks, certain kinds of nitrifying bacteria are produced from the waste. The bacteria convert the toxic ammonia produced by the fish waste into nitrite. Since nitrite is toxic to fish, this again is converted to nitrate by the beneficial bacteria. Nitrate is not toxic, and is used by plants or algae. Prof Wahida Haque, who teaches fisheries at the University of Dhaka, told this correspondent that recirculating aquaculture is a good way of augmenting production of certain species of fish but not suitable for all kinds. She emphasised on proper treatment of the sludge to be generated from such indoor fish tanks prior to disposing those.

The RAS facility of BCSIR is established on 1,800 square feet of land while Agro3's indoor fish farm is setup on 3,000 square feet in Mymensingh's BSCIC industrial area.
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Source: http://www.thedailystar.net/frontpage/indoor-farming-novel-way-fish-yield-1358101

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