Eight people were poisoned by eating tiger groupers at a Kwun Tong restaurant, suffering nausea and numbness in their face and limbs.
They were struck by ciguatoxin poisoning, caused by a toxic marine micro-organism that is passed up the food chain and is found in grouper, snapper and mackerel.
The Centre for Health Protection received two reports of suspected poisoning involving eight people who dined at the restaurant on April 2.
In the first case, a man and three women developed symptoms of ciguatoxin poisoning, including nausea, diarrhoea, abdominal pain and limb, oral and facial numbness, about five to 11 hours after eating the fish.
The second case involved three adults and a seven-year-old child.
They developed symptoms about six to 12 hours after their meal.
None of the patients needed to be admitted to hospital. The centre reminded people to be cautious when eating coral reef fish.
Meanwhile, the centre is investigating an infestation of Chrysomya bezziana - the flesh-eating fly.
A 49-year-old man from Tuen Mun was admitted to Tuen Mun Hospital on Tuesday with pain in the groin and maggots. He is in a stable condition.
It is the second case in Hong Kong this year. Last month a 79-year-old man was found to have an infestation of flesh-eating flies.