Food Safety Focus (69th Issue, April 2012) – Food Safety Platform
Ciguatoxins, Fish and Food Poisoning
Reported by Mr. Arthur YAU, Scientific Officer,
Risk Assessment Section,
Centre for Food Safety
This article is the first of a series of three articles that focus on marine toxins that originate from small organisms (e.g. planktons) which can affect seafood safety.
What are Ciguatoxins and Ciguatera Fish Poisoning?
Ciguatoxins are a group of heat-stable, fat-soluble compounds. They are produced by a marine plankton Gambierdiscus toxicus. The plankton is very specific in where they live and they only exist in the warmer oceans between latitude of 32°N and 32°S. Ciguatera fish are confined to patches of oceans in the area. The toxins accumulate up the food chain which starts with the herbivorous fish that graze on toxic marine planktons in the coral reef, accumulate successively in the body of larger carnivorous fish and finally in humans (Figure 1).
Figure 1. Gambierdiscus toxicus, a marine plankton, can produce ciguatoxins that cause ciguatera fish poisoning in humans. The toxins can accumulate up the food chain and end up causing sickness in consumers.
The toxins are up to 50 to 100 times more concentrated in the viscera, liver and gonads of affected fish, while the fish has no symptom. As the toxins are heat-stable and cannot be removed by cooking or processing, they can affect the nerve and muscle functions of persons who consume fish contaminated with the toxins. Ciguatera fish poisoning (CFP) is now becoming more common as a type of food poisoning worldwide, due to increased international commerce in seafood. CFP is endemic in many areas, including tropical and subtropical Pacific, where many of the locally-sold live coral reef fish are sourced.
How CFP Affects Humans
After consumption of fish that contain ciguatoxins, the initial symptoms can appear within 30 minutes, while a delay of 24 to 48 hours after consumption is common. The initial symptoms can be gastrointestinal or neurological. The gastrointestinal symptoms like vomiting, diarrhoea, nausea and abdominal pain usually last only a few days, the neurological symptoms like tingling of lips, hands and feet, skin itching, change in temperature perception (cold objects perceived as hot and vice versa), fatigue, muscle and joint pain appear later and last longer, sometimes up to a few years. In severe cases, low blood pressure, slow heart rate, respiratory difficulties and paralysis are possible, but death is uncommon.
Factors like previous CFP intoxication, the consumption of alcoholic beverages, nuts and seed products can also increase the sensitivity of an individual against CFP intoxication. Such combination of food items are more likely to be found during banquets locally.
Fish Implicated in Local CFP Cases
Past investigations by the Centre for Food Safety (CFS) show that among the fish species implicated in CFP, certain species of fish are more likely to cause CFP (Table 1). CFS investigations with the trade also suggest that the most frequently contaminated fishing grounds are Nansha Island, Kiribati and Hainan Island. Size of fish involved usually ranges from 0.6 to 3 kg (1 to 5 catties), but fish outside this weight range has also been reported. The information on species and source of fish above may be biased as the information could not be verified. Cultured fish is unlikely to contain ciguatoxins as they are fed with feeds rarely contaminated with ciguatoxins.
Enhancements in Tackling CFP
After the full operation of the Food Safety Ordinance on 1 February 2012, food traders are required to keep relevant transaction records (acquisition records, supply records or capture records as appropriate). Therefore, data collected would be able to provide more accurate information on fish species and their sources. The CFS has issued a Code of Practice on Import and Sale of Live Marine Fish for Human Consumption for Prevention and Control of Ciguatera Fish Poisoning which contains the minimum requirements in importing and selling live marine fish for human consumption to ensure food safety. The CFS also issues advisory letters and newsletter to the traders after each recent CFP incident, providing information on fish source if available.
In the next issue, we shall talk about another locally well-known marine biotoxin that cause food poisoning – paralytic shellfish poisoning toxins.