Tanks to keep fish alive during plankton bloom now in trial phase

Leong Wai Kit Channel NewsAsia 9 Mar 15;

SINGAPORE: Some local fish farms recently lost large stocks of fish as a result of a surge in plankton. Hence, five fish farms have been given grants by the Government to test out new tanks that will keep more fish alive during a plankton bloom.

The tanks are prototypes of what is known as a closed containment aquaculture system. It is basically a controlled environment that blocks out bacteria and plankton.

Sea water is pumped into a container, while a bag filters the sediment. The water is then left to sit for two weeks, to let natural sunlight kill plankton and bacteria. The water will then be transferred to another container, where the fish are kept. So far, the survival rates have been high.

Another feature is a water monitoring sensor that will sound an alert when there are unusual salt, oxygen or nitrate levels in the water.

The prototype was built in November last year, and costs between S$7,000 and S$10,000. The next step is to build a bigger system that can also filter water faster. That will take six months, and cost S$364,000.

Said Mr Malcolm Ong, CEO of The Fish Farmer, one of the five that have been given grants: "We are trying to use technology to reduce the cost of operation and reduce the cost of energy, so that this system will not add extra cost to the fish, and therefore we expect our fish to remain affordable."

During a plankton boom, larger fish can be moved from the open-sea cages into tanks. But small fish reside in these tanks on a daily basis. Such tanks help farms slash the death rate of small fish from 50 per cent, to just 10 per cent.

Said Mr Ong: "We believe that fish grown naturally tastes better, as the flesh will be better. If we put everything in a closed containment system, then the fish’s flesh will not be so good. And that is why we still have the open-sea cage.

"However at the fry stage, where the mortality is very high, we will put it in the closed containment system, so that we can increase the survival rate before we transfer them into the open-sea cage."

The Fish Farmer said it can get up to S$250,000 from the authorities to develop the system, and it will work with the authorities to help other farms build theirs.

The Fish Farmer produces about 800 tonnes of fish per year. About five per cent of its fish were killed during the recent plankton bloom.

- CNA/dl