A species of algae partly responsible for red tides in local waters this week may produce toxins harmful to fish and the humans who eat them, the Agriculture, Fisheries and Conservation Department said.
Tests on samples taken by the department in the East Lamma Channel found that Prorocentrum minimum was one of four algae species responsible for red tides there this week. Citing international studies, a government working group examining the red tides said the species may release toxins.
"Overseas studies showed that Prorocentrum minimum may produce toxins as reported elsewhere. However, no such reports or associated fish deaths have been recorded in Hong Kong," a spokesman for the working group said.
A 2004 study published in the journal Harmful Algae found that shellfish exposed to the algae in the Mediterranean off France contained toxins and posed a threat to humans eating the fish.
Wong Yee-keung, a local algae expert from the Open University, also confirmed that the algae species, found everywhere from cold, temperate brackish water to tropical regions, could be toxic.
The department urged fish farmers at the Cheung Sha Wan, Sok Kwu Wan and Lo Tik Wan fish culture zones to monitor the situation closely. In 1998, a red tide caused by Karenia digitata killed 80 per cent of the stock at Hong Kong fish farms.
Over the past week, the working group reported three sightings of red tides in local waters. The first one was discovered by Marine Police in the East Lamma Channel, including waters off Cyberport and South Horizons, on Saturday.
Tests showed the East Lamma Channel red tide was formed by algae species Pseudo-nitzschia delicatissima, Pseudo-nitzschia pungens, Skeletonema costatum and Prorocentrum minimum.
Two more red tides, caused by Pseudo-nitzschia pungens and Skeletonema costatum, were spotted on April 13 at Silver Mine Bay and from the West Lamma Channel to Victoria Harbour.
The next day, red tides produced by Gonyaulax polygramma were found at seas from Ocean Park to Deep Water Bay.
All the red tides had dissipated by yesterday. There were no reports of associated fish deaths.