They might look like the carved wooden knights of a chess set, be described as having the tail of a monkey, the body of an armadillo, the pouch of a kangaroo and the eyes of a chameleon, yet these bizarre sea creatures have an evolutionary history dating back 40 million years.

No wonder they intrigue, alive in aquaria or dried and sold as souvenirs.

Sadly, since the late 1990s there has been a 64 per cent increase in sea-horse trading; a boom that coincides with, of all things, the introduction of Viagra in 1998. The reason is found in Chinese medicine, for sea horses, dried and mixed with herbs or taken with rice wine or soup, have been used as a cure for impotence by generations of Chinese. It is because they are a cheap alternative to the blue Viagra pill that demand has increased. As China’s trade with the West increases, so perhaps will demand for this remedy. However, sea horses are not only a traditional treatment for impotence, they are also used for ailments as varied as asthma and boils. But can they really be effective?

It is ironic that sea horses are used as a Viagra substitute - of all animals, the male sea horse is more in touch with its female side than any other. The reproductive habits of the sea horse are part of its fascination. It is the only male animal that becomes pregnant. Males and females go through an elaborate courtship ritual lasting several days and including colour changes and synchronised swimming, after which the female puts her eggs in a pouch in the male abdomen, where they are fertilised.

These eggs are incorporated into the lining to form a pseudo-placenta; after about six weeks, the male gives birth to about 200 young. There is no postnatal care; they have to fend for themselves. The parents, however, sustain and strengthen their monogamous relationship each morning by a quivering dance of greeting. Research has shown that a pair will remain faithful to each other even if placed in a tank full of available sea horses of the opposite sex.

Sea horses (Hippocampus) are members of the fish family Syngnathidae, which are found in temperate and tropical waters. Habitats include coral reefs, mangrove swamps and sea-grass meadows. Two species are found in British coastal waters. Their average length is between 10 and 15 cm. The head is set at an angle to the body; it has a coronet and two independently movable, turreted eyes. At the tip of the snout grins a minute, toothless mouth, while their body is enclosed not in fish scales, but armour of bony rings or plates. The finless tail is prehensile, helping anchor the fish to coral. Their single dorsal fin oscillates 35 times a second, looking like a revolving propeller, while pectoral fins move at the same rate. They steer with their head, so the sea horse, which swims stately and erect, just swivels its head in the direction it wants to go. It is not particularly agile and swims slowly in spite of rapid fin movement. It survives in seas crowded with predators, thanks to its mastery of camouflage and ability to change colour quickly. Feeding on small invertebrates as they swim past, sea horses communicate through the clicking sounds they produce as they feed, detecting others close by.

Sea horses are harvested in all seasons but especially during August and September. There are 77 nations trading sea horses with most, about 25 million a year, passing through Hong Kong and Singapore. Yet another danger to the sea horse is the destruction of its natural inshore habitat.

Urbanisation of the shoreline and pollution of the sea are destroying sea-grass meadows and coral reefs. In 2002, 32 of the 33 known species of sea horse were added to the World Conservation Union’s red list of threatened species.

There is some hope: there is now an international effort to help this charming and endangered animal. Aquaria in the UK and abroad are involved in the sea horse conservation programme organised by the Zoological Society of London.

* To find out more visit www.projectseahorse.org