Initial figures showed all 57 cages were affected. Most of the dead fish, weighing 0.5 to 5 kilogramme, were ready for harvest, leaving many households facing heavy losses.
Farmers said they had moved cages to the An Hai anchorage to avoid seasonal winds. From March 31, fish showed unusual symptoms, including loss of appetite, mucus loss and reddening of the abdomen, before dying rapidly and spreading across farms.
Nguyen Van Huy, chairman of Ly Son Special Zone, said authorities were assessing the damage and working with provincial fisheries officials to inspect the site and collect water and fish samples to determine the cause.
“In the immediate term, we are guiding farmers on water treatment and monitoring remaining cages to limit further losses,” Huy said, adding that longer term support and enhanced environmental monitoring would be proposed.