Algae scourge hits fishing ponds

The algae bloom that killed thousands of fish off Singapore's east coast has spread inland.

It has affected fish farms and fishing ponds at Pasir Ris and Changi that use seawater.

The fishing pond at Pasir Ris Town Park, managed by D'Best Recreation, has seen large numbers of its fish go belly-up.

Mr Daryn Ho, 18, who is waiting to enter national service, was with his friends at the fishing pond on March 1 at 11pm.

The four friends paid $172 for fishing rods and some bait for overnight use, but were not told that there was something wrong with the water.

He said: "When we went to the pond itself, there was an overpowering stench of rotting fish and we could see a pile of about 10 dead fish floating in front where we were fishing.

"I was shocked that they did not tell us about it when we paid."

Mr Ho usually brings home about five fish on his weekly fishing trips, but he caught none on his seven-hour overnight fishing session that day.

Two other anglers, Mr Sashi M. K., a business owner, and his brother, Mr Sanjay M. K., a safety officer, go to this Pasir Ris pond about once a month.

Mr Sashi said: "We were told by cleaning staff that they had cleared 300kg of dead fish over the previous weekend."

The place is usually packed with anglers, but when The New Paper went there last Wednesday at 1pm, there were only about 10 people fishing.

The brothers, who are both 30, said they were not aware of what had happened and were only told that the "bite rate was not good" when they approached the counter staff.

SOMETHING WRONG

It was only when they got to the pond that they realised that something was wrong.

Mr Sanjay said: "The fish were behaving abnormally. They were swimming very close to the edge of the pond and sometimes they toppled sideways when swimming to the surface."

The two men usually catch about four fish each on their monthly fishing trip, but they only caught one fish in total that day.

When asked, a D'Best Recreation spokesman said it was aware of its problematic pond water and its dying fish.

It closed the main water inlet to stop affected seawater coming into the pond and added more aerators and water pumps to increase the supply of oxygen for the fish.

Although affected by the algae bloom, D'Best Recreation said it is operating as usual and it claimed that the water is suitable for fishing.

An Aquarium Iwarna spokesman said it noticed a problem with the seawater on Saturday when it noticed the fish floating in the tanks.

However, the fish farm was not as heavily affected because they used preventative measures such as treating raw seawater with ozone or chlorine, and filtering it before use.

It said that even though costs are higher, it guaranteed that the water is safe after the treatment.

Dr Hans Eikees, 43, head of Environmental Technology and Chemistry at DHI, said the algae bloom that caused the fish deaths at inland ponds is the same one that caused fish deaths at sea.

The algae are harmful only to fishes, not humans, and eating fish that have been affected by the algae bloom has no known negative effects on us.

The Agri-Food and Veterinary Authority (AVA) said it is helping fish farmers affected by the fish deaths to recover and restart their operations and enhance their resilience against environmental threats.

Why the fish died

Two main causes for the recent fish deaths in seawater are algae clogging up their gills and suffocating them, and increased ammonia in the water that irritates fish gills, says an environmental expert.

The high level of ammonia in the water comes from the decomposing algae and other organic matter.

The ammonia causes swelling and irritation of the fish gills, and the algae clogs the gills, killing the fish, said Dr Hans Eikaas, 43.

Dr Eikaas is the head of Environmental Technology and Chemistry at DHI, a not-for-profit group offering environmental consultancy and water-modelling services.

For freshwater fish, ammonia is more harmful as it also changes the acidity of the water to be alkaline, making it hazardous for the fish.

He said that algae blooms are a natural phenomenon and can occur in clean, unpolluted waters, but it happens more often in nutrient- rich environments.

There are hundreds of species of algae that bloom, collectively called Harmful Algae Blooms, but he believes the species of seawater algae causing the recent fish deaths is Karlodinium.

It has no known detrimental effects on human health.

When asked why fish deaths have spread inland, he said it was likely they had common causes as the fish deaths at sea.

A prolonged dry period followed by short intense rainfall stirs up sediments that are loaded with nutrients, causing algae and bacteria to thrive.

He feels that fish farms should leverage on technology like chlorophyll and acidity sensors to get a heads up on rising algae levels.

Ideally, farms should isolate the fish from the surrounding water with canvas bags or tanks, or use UV filtration to minimise algae and bacteria numbers.

This article was first published on March 9, 2015.
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