Large numbers of dead fish were found near Lim Chu Kang jetty yesterday morning, washed up on the shore or afloat at sea.
Fish farmers attributed the deaths to low levels of dissolved oxygen in the waters of the West Johor Strait, along which about 50 fish farms are located.
The chief executive of The Fish Farmer, Mr Malcolm Ong, 52, told The Straits Times: "According to my monitoring system, dissolved oxygen levels in my farm have been decreasing since July 8.
"There was a marginal increase on July 12 but after that, it came down again and has remained low since. We have been prepared and our staff are on 24-hour standby."
Mr Ong, who did not lose any fish beyond the normal losses, suggested that low oxygen levels could be an effect of the conditions of the waters near Lim Chu Kang.
"As we are not near an open coast, water is slow moving such that dissolved oxygen levels deplete more quickly," he said.
As we are not near an open coast, water is slow moving such that dissolved oxygen levels deplete more quickly.
MR MALCOLM ONG, chief executive of The Fish Farmer, who suggested that the low levels of dissolved oxygen could be an effect of the conditions of the waters near Lim Chu Kang.
Fish Farmers Association of Singapore president Timothy Ng said such occurrences are frequent in the Lim Chu Kang area. He said: "Unless the environment improves in terms of water flow, this will recur from time to time and I'm not sure how it can be stopped."
Farms tend to install aerators that churn the water and ensure there is sufficient supply of dissolved oxygen when levels are low, although these are not always sufficient to prevent deaths.
However, none of the farms contacted by Mr Ng or The Straits Times suffered serious losses.
Dissolved oxygen levels can also differ from farm to farm, said Mr Ong, who monitors the levels and uses pumps and aerators to mitigate any negative impact on his farm. His farm has had several baby fish deaths this past week, a normal occurrence when dissolved oxygen levels are low.
According to Mr Ong, the Agri-Food and Veterinary Authority (AVA) sent out an automated alert last Friday about the possibility of low dissolved oxygen levels, and asked farmers to be vigilant. AVA did not respond to queries by press time.
Both Mr Ng and Mr Ong ruled out the possibility of a plankton bloom as a reason for the low levels of dissolved oxygen.
In February last year, a plankton bloom, which gobbles up oxygen in the water, killed an estimated 500 to 600 tonnes of fish, affecting 55 out of 63 fish farms along the East Johor Strait.
Farms in the Lim Chu Kang area were also severely affected by a plankton bloom in March last year, with one of the farms losing all 35 tonnes of its fish.