Clay solution to fish farmers' plankton woes?

Clay solution to fish farmers' plankton woes?
Dead fish at Lim Chu Kang jetty in early March.

Dumping clay into the water could be a lifeline for fish farmers here in the event of a plankton bloom, such as the last episode that killed 600 tonnes of fish.

Clay flocculation, also referred to as clay spraying, involves the spraying of clay particles into the water so that they can bind to the plankton before they aggregate and sink to the seabed.

It is one solution the Fish Farmers Association of Singapore will be proposing to the Agri-Food and Veterinary Authority (AVA).

Timothy Ng, the association's president, told The Straits Times that it will submit the proposal in one to two weeks' time, following a members' meeting on Tuesday. The proposal will also include an appeal for financial help to restart their businesses.

Fish farmers here are still reeling from the deadly plankton blooms late last month and early this month, which wiped out almost all their fish stock overnight.

While coastal farms in Changi were most badly hit, those in Lim Chu Kang and off Pulau Ubin were not spared either.

On clay spraying, Mr Ng said he does not know of any farmer here who has tested it.

"We hope we can go on study trips to find out more about it. Currently, what we know is from the Internet," he said.

"We don't want to take the risk and restart our business unless there is some confidence that these methods can work."

According to the United States Environmental Protection Agency's website, clay has been effectively used during red tides in South Korea and Japan. Red tides refer to algal blooms that turn the water red.

Experts, however, warn that more research needs to be done to study its effectiveness in the local context and the impact it could have on marine life.

The plankton said to be the cause of the recent fish deaths here is "much smaller" than the ones found in the algae blooms in South Korea, said Gustaaf Hallegraeff from the Institute for Marine and Antarctic Studies at the University of Tasmania.

"It would be difficult to quantitatively remove these minute cells by clay flocculation," he said.

It should be used only as an "emergency procedure", as settling clay could have "adverse impacts" on bottom-dwelling marine life.

Federico Lauro from the Asian School of the Environment at the Nanyang Technological University added: "If they are planning to use natural clays, the problem is that algae are precipitated, but not killed. Some of the algae can escape and still be deadly to the fish."

Another solution proposed by the farmers is to tow floating fish farms to areas with better water conditions, such as off Pulau Tekong. The use of bags to store fish and a closed containment system are two other methods proposed.

AVA said yesterday it is working with the fish farmers to recover and build up resilience against similar incidents in future.

"This includes putting in place robust contingency plans and conducting contingency exercises," said AVA.

It added that it will help the farmers learn from those who have installed resilient systems.

"Farmers can also tap on AVA's Agriculture Productivity Fund to purchase relevant equipment to enhance their resilience. Beyond these, we are also exploring further assistance for affected farms to restart their operations."

Last Friday, AVA met about 10 fish farmers to discuss how they can move forward, said Mr Ng.

The authority shared with them possible improvements to contingency plans, such as having a colour-coded system to warn them of adverse water conditions.

Stressing the importance of financial help, Mr Ng said: "We have to spend six months to a year growing new fish fry with no income in between."

He added that fish feed usually makes up about 60 per cent of operating costs.

Last year, the Government co-funded a portion of the cost needed to help farmers buy fish fry and new equipment to strengthen their resilience.


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