Warning from the deep

PUBLISHED : Sunday, 25 January, 1998, 12:00am
UPDATED : Sunday, 25 January, 1998, 12:00am

It starts about an hour after a fish dinner, with a mounting feeling of nausea, followed by vomiting, abdominal pain and diarrhoea.

Then, as the toxins take hold, a strange numbness spreads around the mouth. It moves downwards over the next few days as the ability of the nerves to conduct impulses is inhibited. From the shoulders, down the arms to the fingers, and down the legs to the feet.

These are the symptoms of ciguatera poisoning, according to Professor Julian Critchley, head of the clinical pharmacology division at the Prince of Wales Hospital.

Since the beginning of this year, 113 people have been struck by it, compared to 95 cases in 1997, and 305 from 1993 to 1996.

They had all eaten coral-reef fish imported live, sparking worries about the safety of the trade.

'The [gastro-intestinal] symptoms usually wear off in a matter of days,' Professor Critchley said. 'The neurological symptoms usually resolve in a couple of days as well, but in a few unlucky people they can last for weeks. And there are cases of people claiming they've had numbness for over a year.' Ciguatera is caused by a build-up of toxins in fish from poisonous dinoflagellate algae.

And man may be partly to blame. The use of cyanide, which devastates coral, is a favourite method for many fishermen.

There is evidence that destruction of reefs can increase the population of dinoflagellate algae, said Dr Yvonne Sadovy, fish biologist at the Department of Ecology and Biodiversity at the University of Hong Kong.

A 1992 study in the Caribbean showed that the algae flourished on a patch of coral damaged in the construction of a pier, and it is possible that the same happens after coral is killed by cyanide.

Small enough for hundreds to fit on the head of a pin, these algae are eaten by minute zooplankton, which are in turn consumed by shrimps and small fish.

They then become food for large carnivorous fish such as garoupas and snappers, which are much favoured by Hong Kong gourmets.

The toxins cannot be destroyed by cooking.

It has never happened in Hong Kong, but severe ciguatera cases could lead to death, said Professor Critchley, due to dehydration or because of paralysis of the respiratory muscles through nerve damage. But that would take an unusually toxic fish and rare gluttony, he added.

'Even if that happened to you, in Hong Kong you'd have a very good chance of surviving. We'd put you on a ventilator and keep you breathing artificially until you spontaneously recovered. We can ventilate somebody as long as necessary - weeks, months, even years.' According to Dr Gloria Tam Lai-fun, Assistant Director of Health in charge of hygiene, coral-reef fish are randomly subjected to a battery of tests to determine whether they are fit for human consumption, including checks for ciguatera - but only if they are dead.

In the Public Health and Municipal Services Ordinance, which lays down laws on foodstuffs, live fish - along with live animals and birds - are specifically excluded from the definition of food, so they are not tested.

'This is very much an international practice,' Dr Tam said.

'It's nothing peculiar to Hong Kong. I do not see any legal or public health reason for changing the present situation.' Last weekend, the Department of Health warned consumers to avoid fish larger than three catties in weight.

That advice was over-simplistic and misleading because different species of fish grow to different sizes, according to Dr Sadovy.

Laymen would not be able to tell if a fish was large or small for its species, she said.

On Thursday, the Agriculture and Fisheries Department (AFD) issued more detailed guidelines.

The department has been monitoring the trade since January 1997, but to preserve dwindling fish stocks rather than safeguard public health, said Dr Leung Siu-fai, head of the department's fisheries management and marketing division.

Not even the AFD is sure how many live coral-reef fish are imported into Hong Kong each year.

It gets regular reports from the Customs and Excise Department, which compiles figures from import-declaration forms filled in by live fish importers.

But import declarations are not required by local vessels, so the AFD tries to track them through a monthly voluntary verbal survey of mainly land-based traders.

Of about 150 firms involved, 10 have agreed to be questioned, Dr Leung said.

They were believed to be the largest dealers and were thought to control about one-third of the local vessels' catch.

The AFD's estimate for the live coral-reef fish trade last year was 2,100 tonnes, or about 2.1 million fish in total.

But most other estimates are sharply higher.

Dr Vaughan Pratt, president of the International Marinelife Alliance, a Manila-based non-governmental organisation which has been monitoring the business for more than a decade, believes it was over 10,000 tonnes.

One Hong Kong non-governmental organisation says that 10 times the AFD figure would be 'reasonable'.

What is agreed is that Hong Kong is the world's biggest consumer, accounting for around 60 per cent of the trade.

The only other significant markets are Guangdong, Taiwan, and ethnic Chinese in Malaysia and Singapore.

Nor is anyone sure exactly where the fish in the restaurant tanks come from, although Dr Leung said the AFD has 'a general idea'.

That apparent vagueness worries Dr Sadovy.

Ciguatoxic fish which cause ciguatera poisoning are concentrated in distinct 'hot spots', she said.

Some have been identified around the South Pacific archipelagos, such as the Marshall Islands and Kiribati, where fishing boats are now venturing.

'If we knew where live imports were coming from, we could do more careful checking of fish from risk areas,' Dr Sadovy said.

The fact that live coral-reef fish are hunted around those remote islands at all is because reefs closer to the Asian mainland have already been laid waste, largely by cyanide fishing, Dr Sadovy pointed out.

Marine ecologist Dr Bob Johannes, based in Tasmania, has tracked boats arriving in the South Pacific.

'We keep hearing of companies that have moved on,' he said. 'They seem to have to move out further all the time: 'Here's a new island, let's try here.' 'It would appear the Philippines are playing out. If you look at exports of humphead wrasse, which is the most expensive fish and probably the most endangered, there would appear to be none left there. And the numbers are going down rapidly in Indonesia,' he said.

'This industry,' Dr Pratt said, 'is one of the most biologically expensive trades on earth. The amount of damage that's done to collect these fish is devastating to the environment. Once the coral dies you don't have any more fish because there's no breeding. It's a vicious cycle.' Cyanide squirted from plastic bottles by divers stupefies fish by inhibiting their respiratory systems. They can then easily be caught and hopefully revived with a flush of fresh water.

By the time they reach Hong Kong dinner bowls, maybe several weeks later, the fishes' livers have sufficiently broken down the cyanide toxins, so the consumer is not poisoned.

Up to 90 per cent of the live coral reef fish imported in Hong Kong have been caught with this technique, which destroys the sensitive coral, according to Dr Pratt.

Cyanide fishing is an offence in Hong Kong, with a maximum penalty of a $10,000 fine and six months' imprisonment.

The AFD planned to increase the fine to $200,000, Dr Leung said, but the law only applied to offences committed within Hong Kong waters. The AFD does not test arriving fish for traces of cyanide.

Dr Leung insisted that almost all live coral-reef fish imported into the SAR were caught with hook and line.

'But we can't say that 100 per cent [of the fish] are caught with non-destructive methods,' he added.

The International Marinelife Alliance tests batches of fish bound for export from the Philippines for cyanide. In 1991, around 70 per cent tested positive; now it is more like 30 per cent.

By March, Dr Pratt said, the testing could be mandatory there under law.

But the Philippines is a pioneer. And, according to AFD figures, the Philippines were the source of just 2.5 per cent of last year's imports.

In Indonesia, where 80 per cent still came from in 1997, and elsewhere, there was little testing.

For Dr Johannes and Dr Pratt, the ciguatera outbreak in Hong Kong is a stroke of luck, despite their sympathy for the victims.

'We have to stop the demand [for live coral-reef fish],' said Dr Pratt.

'We've had all kinds of education campaigns to make the people in Hong Kong aware of it, but they just don't care.

'We've always said wouldn't it be nice if [the fish] came down with ciguatera because then people would stop eating them. If they stop eating them, they'll stop catching them.'