Thousands of fish have died en masse at waters around Lim Chu Kang jetty and in nearby fish farms.

This has been attributed to the warmer weather recently, according to The Straits Times on April 30, 2019.

Losses of S$3,000 to S$4,000 each

Dead fish started surfacing in Lim Chu Kang waters in the last few days of April 2019, reported Simon Ho, a communications officer at the Fish Farmers Association of Singapore, who cited warmer temperatures as the reason.

Four to five fish farms in the vicinity were allegedly affected, with each reportedly incurring losses of one to two tonnes worth of fish, which amounts to S$3,000 to S$4,000.

Ho added that the fish farmers have since sent out motorboats to retrieve and dispose of the dead fish.

Warmer temperatures lead to low oxygen

Preliminary tests carried out by the Singapore Food Agency (SFA) found that the waters contained low levels of dissolved oxygen.

With the recent rise in weather temperatures, the temperatures of waters increase as well and will lead to decreased solubility of oxygen.

This means that warmer waters are unlikely to hold as much dissolved oxygen as compared to colder waters.

Low oxygen levels in water could also be due to algal or plankton blooms, which are known to proliferate in warm waters.

The growth of algal blooms will then consume large amounts of oxygen, to the detriment of marine life.

This was the case in 2015.

Some 600 tonnes of fish died, severely impacting around 50 fish farms, incurring losses of S$50,000 to S$100,000 for each farm.

However, it is uncertain as to whether algal blooms are behind the fish deaths this time.

"Not unusual"

According to Ho, this incident is "not unusual", as phenomenon like this happen once or twice a year.

Ho, a fish farmer for 10 years, said experienced farmers can tell from the fishes' behaviour when oxygen levels in the water are less than normal — the more active fishes will move less than usual.

Some fish farms also have machines that help replenish oxygen in the waters.

Ho stated that the SFA is currently working with fish farmers to develop contingency measures for similar events in the future, including aerating waters and deciding whether or not to reduce feeding.

Ho also added that such incidents are costs that fish farmers would have to bear from time to time.

He also mentioned the unpredictability of nature.

"With nature, you can never tell. Anything can happen."

Top photo from Jimmy Tan, Flickr