The Seahorse

Relatively few people will have seen the exotic seahorse in its watery environment but the stickleback, which is a far more familiar fish, shares a direct evolutionary link. Along with the Seadragons and Pipefish, seahorses belong to the family Syngnathidae and their scientific genus Hippocampus is from the Greek meaning “horse – sea monster”. Their characteristic shape has even generated the name for the hippocampus at the lower centre of the human brain.

Mythology

Based on vague drawings, the ancients thought that seahorses were the young of the full-sized horses that pulled the mighty chariot of Poseidon (or Neptune) around the seas. However in New Zealand, where there were no horses before the arrival of the Europeans, the Maori name for seahorses is Kiore-moana or sea rats. Interestingly, in an l8th century classification, seahorses were first considered to be insects!

Life-style and Locomotion

Seahorses are unusual in appearance with a horse-like head, neck, prehensile tail, chameleon-like eyes and insect-like body armour, but they are, nevertheless, a species of marine fish equipped with a backbone, gills (unusual grape-like), swim bladder and fins. The scales of the seahorse have over time fused to form the locustlike exoskeleton.

Their only form of propulsion is the dorsal fin that flutters at 35-70 times per second. The earlike pectoral fins control balance and steering. They are poor swimmers, often being killed in heavy storms. To compensate for their poor swimming ability, they have developed a prehensile tail which allows them to grip the eelgrass which in Britain forms one of their preferred habitats.

Each adult Seahorse will consume between 30 and 50 mysid shrimps per day but the Seahorse fry eat up to 3000 very small crustaceans per day (this is why they are so difficult to keep alive). Food is sucked through their snouts and disintegrates as it enters. They have no teeth to chew the food. Their gill pouch is specially adapted to increase the power of the suck. They do not have true stomachs, just a digestive tract through which the food passes. As it goes through, it is only partially digested — another reason why they are so hard to keep.

Life-history

The male occupies territory at the centre of a female’s 5 sq.m. territory and they may pair for life. It is the male that goes through a pregnancy as he fertilises eggs which the female places in his special pouch, the lining of which provides food for the young which can number between 7 and 1572 young in a brood.

These are carried for between two to seven weeks in his pouch before he gives birth to live young which are perfect replicas of the adults. These drift around in the plankton layer for up to 5 weeks; after which, if they survive (only 1 in a 1000 do) they descend to the sea floor and establish a territory. After 4-8 months of growing up, seahorses are ready to mate.

Adult Seahorses have very few enemies, it is the youngsters who take a place in the food chain being more vulnerable to predators (that is probably why so many are born).

Species Diversity

Seahorses are found in every ocean of the world except the Arctic, from the tropics to the cold of the North Sea. There are about 45 species of seahorse, ranging in size from the smallest Pygmy Seahorse Hippocampus Denise — less than 2 centimetres fully grown, right up to the Big-bellied Seahorse Hippocampus Abdominalis at an impressive 35 centimetres. Two new species were discovered in 2003.
Britain has just two species, Hippocampus guttulatus — the Spiny or Maned Seahorse, and Hippocampus hippocampus – the Short-snouted Seahorse.

Habitat

Seahorses live among sea fans, reefs, weed and especially in seagrass. They can camouflage themselves in two ways, firstly by changing colour, and secondly by growing appendages on their bodies to make themselves look very weed-like, but their main defence is keeping still.
Loss of habitat is one of the major threats to sea horses. In Britain this rich, but easily damaged habitat, so important for a large number of important species such as juvenile fish, cuttles, seahares and the snapping prawn, is receiving special attention and includes those within the Fal and Helford.

Man and the seahorse

Each year an enormous number of Seahorses are taken for the aquarium pet trade and many perish within six months.However under well- regulated breeding programmes such as at the National Marine Aquarium, some seahorses have survived for over six years.
The adults have a hard skeleton that looks like bony plates. This skeleton is their downfall – when dead they still retain their attractive shape. One million Seahorses per year are dried into shapes, deliberately killed for the curios trade.
At least twenty million Seahorses are taken for the Chinese medicine trade (£250 a pound) each year to be used as a general tonic, aphrodisiacs, cures for baldness,sore throats, etc. They may have some medicinal properties but this trade is unsustainable.
The export of seahorses, seadragons and pipefishes from Australia needs special permits and in the states of Victoria and Tasmania they can only be caught under permit. Each year the numbers caught are dwindling and many species have become rare and endangered.

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