Spiny seahorse  (Hippocampus histrix)

The spiny seahorse is classified as Data Deficient (DD) on the IUCN Red List (1) and listed on Appendix II of CITES (3).

Named after the spines that project from the corners of the bony plates covering the body (4), the spiny seahorse (Hippocampus histrix) is, like all seahorses, an intriguing and peculiar-looking fish. As well as its spiny appearance, this seahorse can be distinguished by its very long snout (2), which is sparsely patterned with white bars (5). The colour of the spiny seahorse is highly variable, ranging from bright yellow to pale pink or green to match its surroundings (2) (5), and the spines often have dark tips (2). Its independently-moving eyes, which enable the seahorse to scan the surrounding water for potential prey (6), only add to this animal’s bizarre appearance.

The spiny seahorse occurs in the west Pacific Ocean, where it is primarily known from Japan, south to Indonesia and the Coral Sea (5).

Found at depths of at least six metres, the spiny seahorse is often found in water over soft bottoms, amongst soft coral, sponges and sea squirts (2) (5), where there is little or no seagrass (2). It may also be found in shallower areas where algae grow on reef rubble (dead, unstable coral) (5).

While information on the biology of the spiny seahorse is lacking, it is likely to be similar to that of other seahorses (Hippocampus species). Seahorses are ambush predators that wait in the water until prey, such as a small crustacean, other invertebrate or tiny young fish, passes close by its mouth. With a rapid intake of water, the seahorse sucks the prey up into its long snout (6).

The most distinctive and arguably the most interesting feature of seahorse biology is the manner in which they reproduce. During mating, the female deposits a clutch of eggs into a pouch in the male’s tail, where they are fertilised by the male. The male then seals the pouch shut, enclosing the embryos in a protective environment in which the developing seahorses are supplied with oxygen through a network of capillaries. At the end of pregnancy, the male enters labour, which lasts for hours as the male actively forces the young out of the pouch. Immediately after birth, the young seahorses are independent and receive no further care from either parent (6).

Many seahorses are threatened by exploitation for use in traditional Chinese medicines, as well as for curios, souvenirs and aquariums (7). Although the spiny seahorse is known to be collected (5), it is less desirable than some other species for the traditional Chinese medicine trade and is rarely seen in the aquarium trade (2). There is insufficient information to determine to what extent the spiny seahorse may currently be threatened by any such activities, and thus the IUCN has classified this species as Data Deficient (1).

The spiny seahorse is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning that any trade in this species should be carefully monitored (3). It has been recommended that further research is undertaken on this little-known seahorse (1).

View information on this species at the UNEP World Conservation Monitoring Centre.

For further information on the conservation of seahorses see:

• The Seahorse Trust:
  http://www.theseahorsetrust.co.uk/
• Project Seahorse:
  http://seahorse.fisheries.ubc.ca/