Seahorses belong to the genus Hippocampus, hippo meaning ‘horse’ and campus meaning ‘sea monster’ in ancient Greek. Despite this title, they are some of the most loved fish species, and are iconic symbols of the salt and freshwater regions they inhabit.
Seahorses are found in waters less than 20 m deep in coastal tropical and temperate waters. Most are fully marine and live among seagrasses and seaweed, in flooded mangrove forests, soft- bottom or among corals.
Their range is roughly between 50 degrees North and 50 degrees South, with the greatest number of species found in the Indo-Pacific. We have two seahorse species in UK waters, however: the short-snouted seahorse Hippocampus hippocampus and the long-snouted or spiny seahorse Hippocampus guttulatus.
Masters of disguise
Seahorses are masters of camouflage, able to change colour in a matter of minutes to match their surroundings or grow extra skin filaments to imitate fronds of seaweed. They also allow themselves to become clothed by encrusting organisms such as bryozoans and algae to camouflage them even further.
These fish need such extensive camouflage because their body shape is more suited to manoeuvrability than quick getaways. Their dorsal fin is the only source of propulsion and their ear-like pectoral fins below the gills provide stability and steering.
Seahorses tend not to move around much as a result, but use their prehensile tails to anchors onto plants and coral and independently orbiting eyes to look around inconspicuously. This camouflage, their immobility and defensive bony spines are so successful, however, that seahorses have few predators.
An unconventional arrangement
Virtually all seahorse species mate for life and are completely monogamous. In many seahorse species their bond is reinforced with daily greeting rituals where pairs will dance together in the mornings, changing colours, twirling around a common holdfast and promenading together across the bottom with linked tails. Seahorses can also make clicks using their skulls, that are are clearly audible both in and out of the water.
Male seahorses are unusual in that it is they who become ‘pregnant’. At the climax of a 9 hour mating courtship, females deposit large, pear-shaped eggs into the males’ pouch through an egg duct, where the eggs are fertilised by sperm. Male pregnancy lasts between 10 days to six weeks, depending on species and water temperature, after which the male gives birth to fully developed and independent young.
A confiscated seahorse Threats and ZSL’s work with seahorses
Seahorses are severely threatened by overexploitation for traditional Asian medicines, aquarium fishes and curiosities/souvenirs with millions being caught and sold every year. Another big threat is habitat degradation through human activities and climate change
- Our major work with seahorses is through Project Seahorse , founded in 1996 in response to the destructive, global seahorse fishery. It has so far helped to establish 34 no-take Marine Protected Areas and catalysed the protection of seahorses under CITES. Find out more about Project Seahorse .
- We are keeping tabs on the two British seahorses as part of our Thames fish monitoring. In April 2008, new legislation was brought into effect protecting seahorses under the Wildlife and Countryside Act 1981. Find out more about our Thames monitoring .
- We have also had great success breeding these British seahorse species in out ZSL London Zoo Aquarium. Find out about seahorse breeding at the ZSL London Zoo Aquarium
Watch the video about seahorses breeding at ZSL London Zoo: Play this video