Ciguatera: Another Good Reason To Avoid Large Reef Fish

Hongkongers love their seafood – a quick glance at the local restaurants scene will more than proove that point. Per capita HK has one of the highest seafood consumption rates in the world. For many locals, expats and tourists a trip to Sok Kwu Wan on Lamma for a seafood meal would not be complete without a big steamed grouper (also called garoupa). But aside from concerns about over-fishing and sustainability, eating these fish can be a health risk, too. That is because these large reef fish are more likely than others to give you ‘Ciguatera fish-poisoning‘. Ciguatera (‘see-gwa-terra’) is a food born toxin harbored by large reef fish. Originally the toxin (CTX) comes from a microscopic organism called Gambierdiscus. Gambierdiscus is a dinoflagellate – a single-called organism with a thin shell and two beating hair-like whips called ‘flagella’ that move it through the water.

Marine plankton Gambierdiscus toxicus can produce ciguatera toxins (Image taken by Dr. Maria A. Faust, Department of Botany, National Museum of Natural History, Smithsonian Institution, Washington D.C., U.S.A.)
Marine plankton Gambierdiscus toxicus can produce ciguatera toxins (Image taken by Dr. Maria A. Faust, Department of Botany, National Museum of Natural History, Smithsonian Institution, Washington D.C., U.S.A.)

Gambierdiscus sticks to coral, seaweed and algae in tropical and sub-tropical regions (like HK) and is eaten by smaller fish feeding on the coral and algae. These fish in turn are eaten by predator fish and so the toxin moves up the food chain, finally accumulating in its greatest concentration in the large reef fish.

Figure_2_1_sTissues like the roe (fish eggs), head, skin and insides are particularly good at concentrating CTX. CTX is odourless and tasteless and very heat-resistant – so conventional cooking will not destroy or inactivate the toxin.

So how bad is CTX poisoning?

Ciguatera causes a combination of gastrointestinal, neurological and cardiovascular symptoms. The gastrointestinal symptoms include nausea, vomiting, abdominal pain and diarrhoea. That might not be that bad, right? But the cardiovascular symptoms are more serious: a slowing of your pulse to under 60 beats per minute (sinus bradycardia) and low-blood pressure (hypotension) which can be life-threatening but can also be treated. The common neurological symptoms include a sensation of tingling, tickling, pricking, or burning of a person’s skin, numbness of lips, tongue and the four limbs, reversal of hot-cold sensation, muscle pain, muscle weakness, joint pains, itching and fatigue and these symptoms can last for weeks or even months.

CTX in Hong Kong

Because ciguatera is a matter of food safety the HK government requires by law that the reporting of all diagnosed or suspected cases and as a result there are some good statistics on ciguatera in Hong Kong. From 1988 to 2008 there were between 3 and 117 outbreaks annually causing between 19 and 425 people to fall ill. Groupers were responsible for almost 60% of those cases, with snappers causing another 32%. The rest of the cases were caused by moray eels, triggerfish, parrot fish and other reef fish. Past records of ciguatera fish poisoning cases in Hong Kong show that the following fish are more likely to contain ciguatoxins: Moray Eels, Potato Groupers, Speckled Blue Groupers, Tiger Groupers, High Fin Groupers, Hump Head Wrasses, Areolated Coral Groupers, Black Saddled Coral Groupers, Lyretails, Black Fin Red Snappers, Flowery Groupers and Leopard Coral Groupers.

HK Ciguatoxin poisonming cases 1989 – 2008

The most recent suspected case was in September 2014 when a 38-year old man became ill. Before that 19 people aged between 23 and 71 became ill after a shared seafood meal on Lamma in June 2013.

Ciguatoxin cases reported in HK
Ciguatoxin cases reported in HK

Ciguatoxin is very difficult to detect in fish samples so quality control measures are very difficult to implement and suspected cases are often not confirmed because either a sample of the eaten fish is not available anymore or chemical test are not able to detect the ciguatoxin well enough.

How to avoid CTX poisoning

To avoid this nasty CTX poisoning your best bet is to avoid large reef fish especially groupers. Any reef fish over 2 kg in weight is especially risky. And if you do chose to eat such fish stay away from the high-risk body parts of head (sorry, no more sought-after cheek meat), insides, skin and roe (eggs).

coralfish_e

The HK government’s guidelines for the prevention of CTX poisoning are:

  • Buy coral reef fish from reputable and licensed seafood shops. Do not buy the fish if in doubt.
  • Consume less coral reef fish, especially marine fish over three catties (1.5 kg).
  • Only eat small amounts of coral reef fish at any one meal and avoid having a “whole fish feast” in which all the dishes come from the same big coral reef fish.
  • Avoid eating the head, viscera, skin, and roe of coral reef fish which usually have higher concentration of toxin.
  • When eating coral reef fish, avoid alcohol, peanuts or beans as they may aggravate ciguatera poisoning.
  • If you are suffering from ciguatoxin poisoning you should refrain from coral reef fish. The intoxication will sensitize patients and they will suffer from ciguatoxin poisoning even if they are exposed to a lower concentration of toxin.
  • Seek medical treatment immediately when symptoms of ciguatera fish poisoning appear. The unfinished fish should be brought to FEHD (Food & Environmental Hygiene Department) for testing.
  • There is HK Centre for Food Safety Info-Poster on Ciguatera Fish-Poisoning Prevention you can download here.

 

Interesting side notes
  • Ciguatoxins are actually a group of about 20 chemically related toxins. The most potent of these is Pacific-CTX-1 (PCTX-1) which is found in the Pacific Ocean.
  • Ciguatera fish-poisoning was described as early as 600 BC by the Chinese and Captain James Cook’s log details effects felt by his crew on a voyage to Tahiti in 1774.
  • The clinical description of the syndrome came from Portuguese biologist Don Antonio Parra and were published in Havana in 1787. Parra said, “some [fishes] cannot be eaten because they are `ciguatos’ and some others are suspicioned because they carry with them the poison..I can speak from personal experience, because on 15 March 1786, twenty-two of us ate a Cubera, and we all developed those symptoms to a greater or lesser extent. All were prostrated, but each one was suffering various types of discomfort, although the most common type of difficulty was the extreme exhaustion accompanied by more or less pain. I observed that I had extreme difficulty in breathing, which caused great pain and a feeling of suffocation. My tongue became rough and I developed a sour taste in my mouth.”
  • There is commercially available test kit for consumers called Cigua-Check®, however studies have shown it to have a lower than desired reliability and I do not encourage its use over the HK government’s advice cited above.
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Ciguatera Fish Poisoning Case Reported in Hong Kong

The Hong Kong Centre for Health Protection (CHP) of the Department of Health is investigating a suspected ciguatera poisoning case affecting a 38-year-old man. The patient, with good past health, developed symptoms of ciguatera poisoning including facial and tongue numbness, skin itchiness over the forehead and the neck, abdominal pain and diarrhoea about two to three hours after eating a marine fish at home on September 24.
He attended the Accident and Emergency Department of Pamela Youde Nethersole Eastern Hospital on September 25 and was subsequently admitted. He is now in stable condition. The CHP’s investigations are ongoing.

Ciguatera fish poisoning is not uncommon in tropical areas. More than 400 species of fish have been implicated in this food borne illness that’s relatively common in several areas of the world. This toxin is the result of the accumulation of marine algae and the toxins they produce passing up the food chain. These marine algae hang on to dead coral and seaweed. They are then eaten by herbivore fish which are subsequently eaten by predatory reef fish which concentrates the toxin in its tissue.
The toxin accumulates in the fish body, in particular in internal organs, through eating small fish that consumed toxic algae in coral reef seas. A larger fish is therefore more likely to carry higher amounts of the toxin. However, it is not easy to tell from the appearance of the fish whether it contains the toxin. The reef fishes are more likely to get contaminated during storms and other turbulence.

People affected may show symptoms of numbness of the mouth and the limbs, vomiting, diarrhoea, pain in the joints and muscles. An unusual characteristic that is common in ciguatera is temperature reversal. This may be seen from 2 to 5 days after eating the fish. Hot objects seem cold and cold objects can give a shock-like sensation. There have been serious injuries because a person was unable to recognize extremely hot sensations. Other odd symptoms are food may taste metallic and teeth may seem painful or loose.Most people affected by ciguatoxin would recover without long-term health effects, but if excessive toxins are consumed, the circulatory and nervous systems can be affected.
Symptoms may come back after ingesting certain foods and drinks; alcohol, caffeine, nuts and fish.
There are no laboratory tests to diagnose this disease and it’s based on clinical symptoms and a history ofeating an offending fish.

Ciguatera fish poisoning is the most common form of neurotoxin poisoning associated with the consumption of fish in Hong Kong. From 2000 to 12 June 2013, the Centre for Food Safety had received 284 referrals of CFP from the Department of Health (see Figure). A total of 867 persons were affected.

IMG_7061.JPG

Number of ciguatoxins cases from 2000 to 2013 (Up to 12 June 2013)

The reporting of CFP occurred year round. However, it was observed that over 60% of total cases were reported in March to July of the year. The number of person affected also provided similar observation.

Different kinds of coral reef fish caught in the wild were known to be associated with CFP. Black fin red snapper, Tiger grouper, Lyretail, Leopard coral grouper, Areolated coral grouper and Moray eel were the top six common types of fish linked to CFP, accounting for over 50% of CFP cases. Farmed fish which was usually fed by formulated pellet or trash fish was not likely the source of toxins.

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Fish commonly involved in CFP from 2000 to 12 June 2013.

The toxin cannot be destroyed by cooking. To prevent ciguatera fish poisoning, you should observe the following measures:

* Eat less coral reef fish;
* Eat small amounts of coral reef fish at any one meal and avoid having a whole fish feast in which all the dishes come from the same big coral reef fish;
* Avoid eating the head, skin, intestines and roe of coral reef fish, which usually have a higher concentration of toxins;
* When eating coral reef fish, avoid consuming alcohol, peanuts or beans as they may aggravate ciguatoxin poisoning;
* Seek medical treatment immediately should symptoms of ciguatoxin fish poisoning appear; and
* Coral reef fish should be purchased from reputable and licensed seafood shops. Do not buy the fish when the source is doubtful.

Hong Kong Centre for Food Safety Ciguatera page

Red Tides, Fish Kills and iPhone Apps

Here are some images of some pretty right red tide patches. But what on earth is it that makes the water go red like this and is it dangerous?

red tide in DB
Floating patch of red tide in Discovery Bay 4/6/2014

Red tide is the collective name for phytoplankton blooms that tend to colour the water. Phytoplankton is made up of microscopic plants that drift through the sea. When conditions are right (mostly when there is nutrient-rich water and a stable water column) some species of these micro-algae form red tides. Depending on the pigments, the massive growth of algal cells may turn the water into pink, red, brown, reddish-brown, deep green or other colours.

"Pink" Red Tide on Tai Pak Beach
“Pink” Red Tide washing ashore on Tai Pak Beach in Discovery Bay 4/6/2014

 

Red tides are a relatively common sight in Hong Kong with 20-30 reports a year. The immediate reaction from most people is to think that they are the result of some terrible pollution. In fact the phytoplankton species are perfectly natural and normally occur in Hong Kong waters, but under certain conditions they can grow faster and form patches on the sea surface which we call ‘blooms’. Phytoplankton blooms by different species occur all over the world and are often seen by satellites with colour sensors.

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Bloom of the phytoplankton species Emiliania huxleyi in the English Channel as seen from space by a satellite. The light blue comes from the seawater and the white calcium shell of the algal species.

Some red tides produce natural toxins, and can cause depletion of dissolved oxygen or other harmful effects, and are generally described as harmful algal blooms (HAB). The most conspicuous effects of these kinds of red tides are the deaths of marine and coastal species of fish, birds, marine mammals, and other organisms. This happens either as a direct effect of the toxins produced or because of oxygen depletion (known as hypoxia) which happens when the algae die and bacteria consume all the oxygen in decomposing the dead algae.
Only some species involved in red tides however are toxin-producing and cause fish kills. The bioluminescing species Noctiluca scintillans which I wrote about in an earlier post, is not toxic but still can cause red tides.
For Hong Kong this is an economic concern because of the many fish farms and aquaculture areas. When a toxic red tide drifts into a fish farming zone only early warning will help the farmers avoid large economic losses from fish kills by temporarily evacuating their fish cages or transferring their fish to tanks.
The Agriculture, Fisheries & Conservation Department (AFCD) of Hong Kong runs a red tide monitoring network which relies partly on fish farmers and members of the public.  The AFCD follows up reports by taking samples from the red tides and identifying the contributing species under the microscope to determine the risk to aquaculturists and the public. The majority of the reports are caused by non-toxic species. If you would like to know more about the network, the AFCD now has a fantatsitc  app for iPhone and Android (pictured below) with weekly updates and the functionality to report red tide sightings (which I proudly did today) with this new app, including submitting  pictures. (I would also recommend some of the other Hong Kong apps for marine enthusiasts out there:  HK Geopark, Wetland Park, Reef Check, Red Tide Information Network and the WWF Seafood Guide).

 

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The AFCD’s “Red Tide” App for iPhone (also for Android). You can get weekly updates and also report red tide sightings. Available in Chinese (traditional and simpliefied) and English.

 

The AFCD started to record the occurrences of red tide since 1975. From 1975 to 2013, a total of 875 red tide incidents were recorded in Hong Kong waters. Amongst these incidents, only 27 were associated with fish kills.

77 algal species have formed red tides in Hong Kong, but majority of them are harmless. 19 of these species are considered harmful or toxic. Amongst these harmful/toxic algal species, only 5 of them caused 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.

So are there dangers to human health? If a red tide is identified as a harmful algal bloom (HAB) – then, yes, there is a risk:
The consumption of shellfish (e.g. mussels, clams) is one of the most common ways for algal toxins to impact human health. Each species has it’s own toxin so the health effects they cause are also varied. One example is Ciguatera fish poisoning. This type of fish poisoning is caused by eating fish that contain toxins produced by a the marine microalgae Gambierdiscus toxicus, which has been recorded in Hong Kong waters. Barracuda, black grouper,blackfin snapper, king mackerel, groupers and any large predatory fish can carryciguatoxins. People who haveciguatera may experience nausea, vomiting, and neurologic symptoms such as tingling fingers or toes. They also may find that cold things feel hot and hot things feel cold.Ciguatera has no cure. Symptoms usually go away in days or weeks but can last for years. People who haveciguateracan be treated for their symptoms. In Hong Kong with its rapacious appetite for seafood, ciguatera fish poisoning occurs quite frequently. For example, in 2004 it made up 7.9% of all food poisoning cases recorded that year. In June 2013, fourteen men and five women, aged 23 to 71, fell ill with ciguatera poisoning after eating coral reef fish at a restaurant in Sok Kwu Wan (Lamma Island). The fish in this case actually came from the Pratas/Dongsha Islands out in the South China Sea. Ciguatoxin’s is very stable, so cooking, drying or refrigerating fish will not destroy the poison. There is also no effective way to test fish for ciguatoxin, yet. If you want to play it safe avoid large predatory fish like tuna, grouper and others alltogether (they are mostly overfished already, especially blue-fin tuna, so you would be doing the planet a big favor).

So eating shellfish or fish which has been exposed to HABs is the main danger to humans. There are instances of skin irritations and breathing difficulties after direct human exposure to HABs but these are rarer and not as well understood. So to be absolutely safe, I would advise you to avoid contact with red tides – no swimming in, diving under or touching them!