Last week, the creatures were added to a global watch-list of endangered species, obliging Hong Kong and 160 other countries and territories around the world to monitor the trade in seahorses and prohibit the sale of specimens under 10cm in length.

There is an irony in the use of seahorses as a means of boosting virility. Modern research has established that, if anything, the male of the species is more in touch with its feminine side than anything else in the animal kingdom.

Seahorses are unique in being the only species in which the male gets pregnant. The female injects eggs into the male's pouch, where the eggs are fertilised and carried for up to four weeks until they are born.

Seahorses can also lay claim to being the most romantic creatures on the planet, performing a dainty daily underwater dance with partners and generally staying faithful for life - even, as experts have found, if they are placed in a tankful of single, available seahorses of the opposite sex.

More than 20 metric tonnes of dried seahorses are annually imported to Hong Kong - which with Singapore is the world's biggest trading hub for seahorses - from 20 different countries.

By 2001, the last year for which comprehensive figures were available, global consumption had reached 70 metric tonnes - equivalent to 25 million seahorses - compared to just 45 metric tonnes seven years earlier, and there is every sign that the trend is continuing.

And it all comes down to impotence, said Samuel Lee Kwok-hung, Hong Kong representative of the Marine Medicinals Conservation Programme, a joint initiative by conservation watchdog Traffic East Asia and the US-based research group Project Seahorse.

'In Hong Kong itself, consumption is not that huge,' Mr Lee said. 'The majority of the demand is from mainland China. Seahorses can be used for a variety of treatments including asthma and for impotence and sexual dysfunction.

'With China becoming more and more open for foreign investment and for exporting products out of China ... the trade in traditional Chinese medicine is on the whole increasing.'

Spiralling demand is meanwhile driving the dragnet further and further afield. Last year, South American countries including Peru and Mexico accounted for 3 per cent of imports while another 2.1 per cent came from African countries such as Mozambique and Gambia.

Hong Kong traders say the potential sales are 'limitless', raising concerns among conservationists that the trade will continue to gather pace even as the global numbers of seahorses decline.

A number of factors make seahorses more vulnerable to depopulation: small brood sizes and low levels of mobility make it slower for numbers to grow, and their 'one partner for life' tendencies make widowed seahorses reluctant to find a new partner.

They are also highly vulnerable to the dangers of their environment. Up to 50 seahorses are born at a time, yet few reach maturity due to an array of predators including crabs, tuna, skates and rays. Adults are vulnerable to the elements and many die in storms from exhaustion or being thrown ashore.

Last week's move will be a lifeline for the 34 species of seahorses. They were added to the list of protected species under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (Cites), meaning all 166 member nations will be required to regulate the cross-border trade in the sea creature.

Export permits will be required and trade will only be allowed if there is no threat to the wild populations of that species.

A spokesman for the Agriculture, Fisheries and Conservation Department said Hong Kong's Animal and Plants Ordinance had been altered as a result of the move and import and export licences would be required for seahorses from June 1.

'Because of this, we will know the trade better in one or two years,' said Mr Lee, who said the most important aspect of the Cites listing was the prohibition in the trade of specimens less than 10cm in length. Seahorses range in length from 2.5cm to 25cm.

Project Seahorse is keen to stress it is not calling for an end to the use of seahorses in traditional Chinese medicine. In developing countries, it is often the only affordable form of treatment and its rise in popularity in parallel with the Viagra phenomenon in the west is understandable. What's more, the medicines they are used in appear to be effective and boast six centuries of satisfied customers.

'We can't say 'don't buy seahorses',' said Mr Lee. 'Rather, we are asking people to use them in a sustainable way. If we collect more information, we will know more about the impact the trade has on the world population.'

The Cites listing would have an important impact on source countries. 'In the past, exports may not have been properly reported or declared to customs,' said Mr Lee. 'Now they need to abide by the Cites requirements or the penalty will be huge.'

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