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White's Seahorse
Hippocampus whitei Bleeker, 1855

Common name

White's Seahorse

Scientific name

Hippocampus whitei
hippo - horse (Greek)
campos - sea animal (Greek)
whitei - named after John White, Surgeon General to the First Fleet

Family name

Syngnathidae
syn - together, with (Greek)
gnathos - jaw (Greek)
idae - suffix meaning that this a family name. All animal family names end in -idae. The family name refers to the tubular snout and small jaws of fishes in this family.

Size

Seahorses range in size from 2.5 cm to 35 cm in length. White's Seahorse commonly grows to 20 cm in length.

Number of species

The family Syngnathidae contains the seahorses, seadragons, pipefishes, and pipehorses. There are 200 or more species in the family, about 35 of which are seahorses (all in the genus Hippocampus). The seahorses are not well known and further scientific study is required on the family. The strange-looking ghostpipefishes, (family Solenostomidae), are related to the seahorses.

Distribution

Fishes of the family Syngnathidae are found in tropical and temperate coastal waters around the world and seahorses occur throughout this range. White's Seahorse however, is endemic to (only found in) Australia. It occurs in depths down to about 25 m in temperate marine waters along the south-eastern and south-western coasts of Australia. It is common in Sydney Harbour.

Habitat requirements

White's Seahorse occurs in a variety of habitats. It can be found in shallow protected waters in seagrass, algae beds and under wharves. The image below shows White's Seahorse between blades of seagrass at Camp Cove, Sydney Harbour.

The Big Belly Seahorse Hippocampus abdominalis ( View images 1, 2), which is also widespread in south-eastern Australia, can be found in similar habitats to that of White's Seahorse, and also in deeper water living on sponges.

Structural, physiological and behavioural adaptations

Seahorses are beautiful fishes with some remarkable adaptations including hard bony armour on the body, a prehensile tail (which can be used for holding on), binocular vision, excellent camouflage and a most unusual mode of reproduction. Seahorses have appeared on charms, talismans and ornaments and even featured as the figurehead on Captain Cook's vessel, the Resolution.

Hard bony armour

All seahorses have bodies that are protected by strong external plates which are arranged into a series of 'rings'. These rings help to protect the body of the fish, but result in the fish having only limited flexibility of the body . The number of trunk (body) and tail rings doesn't vary much among individuals of a species, but does differ between species, so it is a handy character for telling species apart. White's Seahorse has 11 trunk and 33-36 tail rings.

Seahorses lack a caudal (tail) fin, and since this fin provides most fishes with their main swimming power, seahorses don't swim very fast. They are however very manoeuvrable, and can hover very precisely. They can swim forward or backwards by undulating their dorsal and pectoral fins.

The fins and rings of a generalised seahorse are labelled on the figure above. Also shown is the coronet on the top of the head. Differences in coronet shape are useful in separating species. Compare the coronet of White's Seahorse in the image above with that of the Big Belly Seahorse.

Prehensile tail

Seahorses all have a prehensile tail. This allows the fish to hold on to objects such as seagrass with its tail. The image at the top of this page shows a White's Seahorse holding on to a piece of encrusted fishing line under the jetty at Clifton Gardens, Sydney Harbour. The Big Belly Seahorse can be distinguished from other Australian seahorses by its deep body and higher number of trunk and tail rings. Unlike many other fishes, seahorses have no tail fin.

The image on the right clearly shows the prehensile tail of a White's Seahorse.

Eyes

Like all fishes, the eyes of seahorses can move independently. Because of their placement, it is believed that seahorses have binocular vision. This would help in catching the small crustaceans which make up much of the diet.

The image on the right shows the head of a White's Seahorse. View larger image

Reproduction

The reproduction of seahorses is truly remarkable (view detailed fact sheet). The male seahorse has a pouch (a marsupium) into which the female seahorse lays her eggs. In White's Seahorse, the male fertilises the eggs and cares for them for about three weeks (depending upon several factors including the temperature). During this time, he aerates the pouch, and most remarkably of all, nourishes the eggs through a capillary network in the pouch with his own 'placental fluids'. At the end of the 'pregnancy', the male gives birth to 100-250 fully formed young seahorses of about 1 cm in length which swim away to care for themselves. The male then 'becomes pregnant' again almost straight away. White's Seahorse is monogamous (females and males form permanent pairs) and breed from October to April. View image (and another) of a male seahorse giving birth and juveniles after birth.

Camouflage

White's Seahorse is usually very well camouflaged in various shades of brown, grey and black. Some species of seahorses even have encrusting organisms growing on them to further enhance their camouflage. Their colouration, combined with secretive behaviour, often makes the seahorse very difficult to spot in its natural habitat. Seahorses in general are known for their ability to change colour depending upon their habitat, what they have eaten, and also as part of courtship and 'greeting rituals'. During the greeting ritual, White's Seahorses change from their usual sombre colouration into far brighter shades of cream and yellow.

Seahorse relatives such as the pipefishes are also known to be exceedingly difficult to spot at times. Try finding this pipefish.

Feeding

Feeding in seahorses is very specialised and involves a rapid upward movement of the head, a lowering of the floor of the mouth, (which increases its volume), and opening of the mouth. All three occur almost simultaneously, resulting in prey being sucked in through the mouth and up the long tube-like snout.

View a low resolution movie clip (56k) of this species feeding. Go to the movies page for high and low resolution versions.

Follow-up questions

Name another family of fishes which has species that lack a caudal (tail) fin.
Seahorses are sold commercially in parts of the world. This has led to serious declines in some seahorse populations. How are these seahorses used?
What is unusual about the gills of seahorses?