Wanted: A 'closed system' to protect fish stocks

Feng Zengkun The Straits Times AsiaOne 9 Oct 14;

Fish farmers in Singapore hurt by massive die-offs in recent years could soon get help to prevent them from happening again.

The Agri-Food and Veterinary Authority (AVA) has asked firms for proposals to design and develop a "closed containment aquaculture system" to help the 116 coastal fish farms here.

Most of the local food fish supply is produced by farms using open net cage systems, made up of net cages submerged in the sea to house the fish.

"The fish stocks are exposed to environmental changes which the farmers have no control over," the AVA said, adding that massive algae blooms and spills from maritime activities could harm or kill the fish.

In January and February, 39 coastal farms lost 160 tonnes of fish due to plankton blooms, the latest in a series of die-offs in recent years.

Experts said there are several methods to prevent such problems, including two closed containment systems - the flowthrough system and the recirculated aquaculture system (RAS).

They told The Straits Times that, unlike net cages, these systems separate the water where the fish are kept from the water in the natural environment.

These can be tanks or bags submerged in the sea or placed on barges or on land.

In the flowthrough system, sea water is treated as it flows into the tank to remove potentially harmful bacteria, viruses and algae. It is then cleaned up again before it flows out of the tank.

"In recirculated aquaculture systems, you pump in the water once and it is recycled over and over again," said Dr Guillaume Drillet, a marine biologist dealing with aquaculture at research and consulting group DHI Water and Environment.

These systems give fish farmers control over the water quality, but are considerably more expensive than net cages due to the technology involved.

Singapore Aquaculture Technologies, a seabass farm near Pulau Ubin, has installed both the flowthrough system and RAS.

Co-founder Dirk Eichelberger said its RAS, which can hold 20 cubic metres of water, costs $50,000, while a flowthrough system is $25,000 to $30,000 for 50 cubic metres. "The systems get cheaper as you scale them up," he said.

The hefty investment is worthwhile, he added, as the closed systems can support up to 50kg of seabass per cubic metre, compared with just 15kg for the net cage systems.

Fish farms here must produce 17 tonnes of fish per 5,000 sq m of farm space a year to keep their licences. Dr Eichelberger said: "In the same amount of space, with this technology, we believe we can produce 250 tonnes to 400 tonnes.

These systems could help improve Singapore's food security by a lot."

The AVA said that if a suitable system is developed, fish farmers will be able to tap the Agriculture Productivity Fund to install it.