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History of red tide / HAB in Hong Kong

History of red tide / HAB in Hong Kong

The Agriculture, Fisheries and Conservation Department (AFCD) started to record the occurrences of red tide in Hong Kong waters since 1975. From 1975 to 2023, a total of 995 red tide incidents were recorded in Hong Kong waters. Amongst these incidents, only 28 were associated with fish kills.

A total of 86 algal species have been recorded to form red tides in Hong Kong, but the majority of them are harmless. 24 of these algal species are considered as harmful or toxic. Amongst these harmful / toxic algal species, 5 of them resulted in fish kills and the other two caused contamination of shellfish by toxin in Hong Kong. The red tide associated fish kill events were mostly recorded in the 80's and early 90's.

Algal species causing harmful effects on fish 
Karenia digitata
Chattonella marina 
Chattonella marina var. ovata

Algal species producing shellfish toxins  
Alexandrium catenella
Alexandrium tamarense
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