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What should we do in red tide incident?

What should we do in red tide incident?

Fish farmers

A flag system is used to facilitate dissemination of early warning messages to mariculturists in fish culture zone.


For non-toxic red tide:

For non-toxic red tide but with a chance to cause oxygen depletion, a yellow flag is raised to remind the mariculturists to check closely the dissolved oxygen levels in the water, stop feeding the fish to slow down the metabolism of fish and to get ready to aerate the water when oxygen depletion occurs.



For toxic red tide:

For toxic red tide, a red flag is raised to alert mariculturists to prepare for early harvesting or raft relocation to avoid the toxic red tide and reduce the loss of fish.



Mitigatory measures


For non-toxic red tide:
Increase the oxygen content in the water by aeration using compressor, Venturi nozzle in case of oxygen depletion
Stop feeding the fish to reduce the oxygen consumption of fish and ecosystem

For toxic red tide:
Relocate the fish rafts to area clear of the toxic red tide
For short-term mitigation, enclose the fish cages with the plastic sheets to separate fish from the toxic algae and aerate the water in the cage.

Aeration by Venturi type nozzle
Enclosed fish cage with plastic sheets



Please report the sighting of red tide to AFCD including details about the location, colour of the seawater, extent of the red tide, occurrence of dead fish and other abnormal condition of the environment.

When a red tide is sighted at a bathing beach or when a red flag is hoisted at the bathing beach, avoid swimming and contact with red tide.

If any symptoms of illness observed after contact with red tide or consumption of contaminated seafood, you should seek medical advice as soon as possible.

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