WITH no new dead fish spotted since last Saturday, fish farmers hit by the recent plankton bloom have started moving their stocks back to open waters.
Over the past two weeks, large numbers of fish - more than 600 tonnes in total - have died, with farms near the East Johor Strait the worst hit. This amounts to more than 10 per cent of annual production, affecting more than 55 out of 117 floating fish farms.
Losses have been estimated at between $15,000 and $300,000 per farm, and could total between $4 million and $5 million. But farmers believe the current wave of deaths could be over. "Even the wild fish are returning to the area," said Mr Malcolm Ong, 51, CEO of The Fish Farmer.
Some affected farmers such as Mr Ong have begun importing new batches of fish fry, or baby fish. He had a batch of 10,000 delivered this week, and has another delivery planned for next week.
Mr Frank Tan, 40, who owns Marine Life Aquaculture, started restocking on Monday, and believes the water quality at his Changi farm has improved. "We don't
see any more algae in the sea, but it could be on the seabed or hiding somewhere," he said.
He also moved his surviving fish back to open sea cages after transferring them to inland tanks on Pulau Ketam when the plankton bloom struck.
Mr Wong Jing Kai, 26, of Ah Hua Kelong moved some of his surviving stock back to sea as early as Wednesday last week after noticing improvements in the water quality. However, he does not discount another plankton bloom in the near future: "It is unpredictable; there is no pattern to it."
Experts say the most accurate way to find out if plankton levels are normal is a water quality test.
As a rule of thumb, there should only be a few hundred cells of dinoflagellates per litre, according to Associate Professor Federico Lauro of the Singapore Centre on Environmental Life Sciences Engineering at Nanyang Technological University.
Dinoflagellate is the type of phytoplankton which caused the mass fish deaths. During a bloom, they multiply to tens of thousands or even millions of cells per litre.
Plankton blooms can be deadly as the plankton suck oxygen from the water, suffocating other marine life. They can be caused by unfavourable environmental factors such as a neap tide, where there is a very small difference between high and low tide levels, dry weather or pollution.
Prof Lauro said it is tempting to regard the lack of new deaths as an indication that the water is now safe, but he cautioned: "Nobody can say for sure without specific monitoring."
Mr Chan Wei Loong, programme chair of Republic Polytechnic's diploma in marine science and aquaculture, said that since the life cycle of a plankton bloom is about a week, chances are that the water has cleared up.
He added that the recent rain should have helped as plankton thrive on warm temperatures and sunlight.
Meanwhile, the National Environment Agency has declared the water quality at Pasir Ris, Changi and Punggol beaches within recreational water guidelines, after its latest round of water sampling.
But some farmers are still cautious. Mr Phillip Lim, 53, former president of the Singapore Marine Aquaculture Cooperative, is coming up with a new farming system to protect his fish from sudden environmental changes. He said: "I am not bothering to restock, I am not going to take the risk."
This article was first published on Mar 14, 2015.
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