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.

Noctiluca scintillans Makes Global Headlines for HK

As reported by Apple Daily today, a recent bloom of the bioluminescent organism Noctiluca scintillans – often known as “Sea Sparkle” – and a frequent cause of red-tides in Hong Kong (recent posts here, here and here ), has occcured in the sea near Tai Po. The bloom has attracted more and more people hoping to capture the bioluminescence on camera. Some of the images and video have even made international media reports.

But the sudden influx of night-time visitors is causing some aggravation to villagers who are complaining about the noise nuisance. Many people have also been throwing rocks into the sea to agitate the single-celled organisms into sparkling, which is harming the local ecology.  While one or two stones thrown hardly make a difference, several hundred rocks hurled into the sea does create some damage. If you are reading this and planning to go and see the blooms, please DO NOT THROW STUFF IN THE SEA, NOT EVEN STONES. If you really want to see the sparkle then wade in to use your hands or a stick to agitate the water – but I don’t advise this either.

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Some villagers have now taken to blocking beaches. Up to 100 visitors are coming to the beaches and cars are now blocking lanes causing a major disturbance to village life.

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Advice on viewing Noctiluca scintillans in Hong Kong:

1. DO NOT THROW ANYTHING INTO THE SEA. If you want to agitate the bloom use a stick or branch to swirl the water. Or just watch out for waves which will do the same.

2. Respect local villagers. Do not be noisy and obnoxious. Do not block lanes

3. DO NOT LITTER. TAKE ONLY PICTURES AND VIDEO, LEAVE NOTHING BEHIND.

4.  Use a tripod and a slow shutter speed and high sensitivity (ISO) for long exposures to capture the full sparkle.5. If you can tame your urge to see the sea sparkle in person please do, it would really help the environment (and the villagers). You can just enjoy the images and videos floating around the internet,for example this (probably copied) video:

Click here to see irresponsible behaviour in the Apple Daily article ( so you know what not to do).

Short-Finned Pilot Whale Washes Up Dead Near Nim Shue Wan, Lantau

It appears that shortly after the first sighting of a short-finned pilot in Hong Kong (see post from January 14th), we now have the first stranding of a dead short-finned pilot whale. Ocean Park’s Cetacean Stranding Response Team investigated an adult female short-finned pilot whale stranding case today at Cheung Sha Lan, Discovery Bay. It’s 365cm long and as the carcass was severely decomposed, the cause of death cannot be determined. The Team and a veterinarian have done a necropsy on site. The preliminary findings show:

• A 12cm superficial wound was found near the fluke, though it unclear if this is pre-mortem or post-mortem
• A thin blubber layer of 1.5cm (mean blubber layer thickness of adult female short-finned pilot whale is 1.91cm), indicating that the dolphin was relatively thin and weak

Image: OPCF
Image: OPCF
Image: OPCF
Image: OPCF

The team sent the head, flippers and dorsal fin to Hong Kong Veterinary Imaging Centre for Computed Tomography (CT) scanning, and collected tissue samples for further testing.

Many people asked if this short-finned pilot whale is the same one people sighted at Tsim Sha Tsui on January 13. The dorsal fins on cetaceans have unique characteristics that allow identification of individuals, but since the dolphin’s dorsal fin was severely decomposed, no identification can be made as yet. Yet, as short-finned pilot whales are rare in Hong Kong, and the length of the carcass is similar to the estimated length of the pilot whale sighted in Tsim Sha Tsui (about 3 meter), the possibility can not be ruled out that they are the same individual.

In case you are wondering how this white carcass could have come from a black short-finned pilot whale: this often happens to decomposing whales and dolphins. I once saw a 0.5 m Finless porpoise washed up dead at the Cape D’Aguilar Marine Reserve. Normally Finless Porpoises are black, but the carcass was also white.

Before and After Images of Dolphin Injured by Boat Propeller

The dolphin recently spotted with terrible dorsal fin and back injuries likely caused by an outboard motor has been identified as an individual frequently spotted in Hong Kong waters off Lantau Island (see map below). The individual designated WL212 was identified by cross-referencing against a photographic database of dorsal fin markings. This allows us to make the before and after comparison of the injuries in the featured image courtesy of the HKDCS (HK Dolphin Conservation Society).

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All images from HKDCS

Chinese White Dolphin’s Back Slashed Likely Caused by Outboard Motor

A Chinese white dolphin was spotted off the coast of Tai O with slash injuries across its fin and back believed to have been caused by a collision with a tour boat’s outboard motor.

Despite the injuries – some of which appear to be several inches deep – a marine scientist who observed the dolphin believes it still has a fighting chance. But tour guides operating dolphin-spotting excursions were warned to steer clear of it.

The dolphin was found near Tai O village at around 4.30pm on Saturday (17th of January 2015). Video and photos taken by members of the University of Hong Kong Swire Institute of Marine Science, clearly show the dolphin swimming along with large gashes on its back and tail.

Dolphin Conservation Society chairman Samuel Hung suspected they have been caused by propeller cuts from the outboard engine of a walla-walla – a type of small motorboat common in local waters which are often seen in the area for dolphin-spotting tours.

“The injuries are very serious,” said Hung, but despite the cuts the dolphin appeared “surprisingly tough” and was seen swimming, rolling around and even feeding on fish near the water’s surface.

Many more motorised tour boats arrived at the scene to view the injured dolphin by late Saturday afternoon putting the animal at greater risk. Hung urged all tour boats not to get too close to the dolphin. He also said that at this point, based on its behaviour, the dolphin would not require further intervention such as rescue or rehabilitation. “The last thing we want to do is to disturb this animal further,” he said.

The 2013 survey estimate of the number of dolphins in west, northwest and northeast Lantau areas is 62 dolphins (similar to the 2012 estimate). That is the lowest of the past decade.

News: Pilot Whale in Spotted Hong Kong Harbor

A pilot whale was spotted yesterday morning (13th January 2015) at about 10 am off Tsim Sha Tsui between the Ocean Terminal and the busy China Ferry Terminal. Unnamed experts identified the apparently 3-m long whale as short-finned piloit whale (Globicephala macrorhynchus), which can grow to 6.5 m in length (figure quoted by The Standard) – but you will find estimates of up to 7.3 m in the literature. That would make this whale a juvenile or young adult. It lingered there for approximately 3 hours before dissapearing again.

Short-finned pilot whales are rarely seen on their own and tend to appear in groups of 10 – 30 sometimes up to 50 individuals and prefer deep-water. A juvenile lone short-finned pilot whale in Hong Kong’s shallow waters is therefore sadly no cause for cheer – more of a sign of being lost, injured or sick. The video footage (below) seems to show some surficial insuries to both sides of the head as well as the lower frontal edge of the dorsal fin.

You can see more footage in the article from Apple Daily’s local news site.

Some readers may remember a similar-looking species of whale – the false killer whale – showing up at about the same time of the year in 2014 near Kwai Tsing Container Terminal. In that instance it was a group of possibly up to 100 individuals which later on left Hong Kong waters again. There is some video footage of that event I posted here.