DONG THAP - More than 150 tonnes of red tilapias have died en masse in the past week in Cao Lanh District in the southern province of Dong Thap, resulting in losses of VND35 billion (S$2.2 million) for aquaculture farmers.
Red tilapias are the world's most popular farmed fish. They are fast growing and low in mercury.
The dead fish were being raised by 41 households along the Can Lo River. It was the first time such a disaster has occurred.
"Tests on the fish and water samples reveal the deaths were caused by frequent ebb tides and the high densities of fish kept caged in pens," said Vu Thi Nhung, head of the provincial Department of Natural Resources and Environment's Environmental Protection Division.
The tests were conducted by the department and Can Tho University. Nhung added that ebb tides created high amounts of organic substances in the water, which helped make oxygen levels below regulated levels.
The density of the fish in pens was 130-200 per square metre, much higher than the 90-150.
"The more organic substances deposited, the less oxygen in the water. This is what killed them," said Nhung.
She added that the department did not have any plan to support local farmers who lost their fish. But it will hold training courses to make sure farmers understand the proper technology for raising the fish.
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