‘Unprecedented disaster’ for Hong Kong fish farmers: deadly red tide kills 36 tonnes of stock

A surge in a rare but harmful species of fish-killing red tides has devastated stocks in Hong Kong waters this winter in what is described as an unprecedented disaster for fish farmers.

Virtually all reports of the algal bloom involved the karenia papilionacea or karenia mikimotoi species, both of which are harmful to fish, with the latter a proven killer due to its effects on the gill tissues of fish and their breathing systems.

A Post review of statistics on the Agricultural, Fisheries and Conservation Department’s Red Tide Database from last November to the end of January indicate that most red tide reports were concentrated around Tolo Harbour and Long Harbour in the eastern New Territories.

The red tides have been linked to a massive fish kill in the area. Since late December, more than 36 tonnes of fish have died off mariculture zones in Kau Lau Wan, Yim Tin Tsai, Sham Wan, Yung Shue Au, Lo Fu Wat and Tap Mun.

Red tides, or algal blooms, are areas of seawater discoloured – brown, pink or red – by large concentrations of microorganisms that may deplete levels of dissolved oxygen. Sightings usually peak in the spring.

While there were more reports of red tides in the same period of 2014-15, distribution was more or less evenly spread, with just as many sightings around Lantau Island, Lamma Island and Tung Wan. But the red tides that winter were nearly all formedby the noctiluca scintillans species, which is non-toxic and commonly found in Hong Kong waters.