Common seahorse  (Hippocampus kuda)

Classified as Vulnerable (VU A4cd) by the IUCN Red List 2003 (1). All seahorses are listed on Appendix II of CITES (3).

The common seahorse is a relatively large species, which is not common as the English name suggests, but is classified as Vulnerable by the IUCN Red List of Threatened Species (2). Like all seahorses, the head is held at right angles to the body, the eyes can move independently of each other, and the tail is prehensile. Instead of having scales, as in most other fish, seahorses have a layer of skin stretched over bony plates that are visible as rings passing around the trunk (4). Swimming is powered by the rapidly oscillating dorsal fin, and they steer using the fins on either side of the body (the pectoral fins) (5). The common seahorse has a deep head and body and a thick, robust snout. Individuals are often completely black or they may be yellowish or cream with large dark spots. In common with other seahorses, this species is a master of camouflage, and may occasionally be sandy in colour in order to blend in with the background (2).

Found throughout South East Asia, Australia, Japan and some Pacific islands (including Hawaii). There is much confusion as to the taxonomy of this seahorse, and the name Hippocampus kuda has been widely applied to all non-spiny seahorses in the region, however further research is needed to fully understand the status of this seahorse (1). Surveys on seahorse trade carried out by Project Seahorse in 2000 and 2001 have shown that the populations of this species have declined throughout the entire range, with fishers reporting massive decreases (1).

Typically inhabits shallow waters, in estuaries, reefs and on mud slopes where there is seagrass or marine algae. They have also been found in open water and attached to drifting vegetation up to 20 km off shore (2).

Perhaps the most unique and unusual feature of seahorse biology is the fact that it is the male and not the female who becomes pregnant. When mature, males develop a pouch on the belly, known as the brood pouch. Breeding takes place in spring and summer; the female inserts her ovipositor into the male’s pouch and lays her eggs. The male then fertilises them and they become embedded into the wall of the pouch. The pouch is very similar to the womb found in female mammals; a placental fluid removes waste products and supplies the eggs with oxygen and nutrients. As pregnancy progresses, this fluid gradually becomes similar to the surrounding seawater, so that when the young seahorses are ‘born’ the change in salinity is not too great a shock (4). After 20 to 28 days of pregnancy the male goes into labour, typically at night when there is a full moon (2) (4). After hours of thrusting, the miniature seahorses, which look exactly like the adults, are released from the pouch. (4). The offspring are fully independent after birth and must fend for themselves (4). They are pelagic in the first stage of life, or hold onto floating debris at the surface with their tail (4).

Seahorses are ambush predators, and lie in wait for small crustaceans to swim by; they then suck the prey into the tube-like mouth and swallow it whole, as they do not have any teeth (5). They do not have many natural predators, as they rely on their excellent camouflage for protection, and they are unpalatable due to their bony-plated bodies (5).

This species is sold locally and internationally for use in traditional medicines, in the aquarium trade and as curios (1). It is one of the most valuable seahorses in traditional Chinese medicine and is very popular as an aquarium species. In 2001, the global consumption of seahorses was estimated at 25 million seahorses (over 70 metric tonnes) (3). Furthermore, habitat degradation and pollution in some areas reduces the available habitat for the species, and it is also often accidentally caught as by-catch in the shrimp-trawling industry (1).

The most pressing requirement to assist in the conservation of this species is the need for further research. In order to effectively conserve a species, its biology, ecology, range and abundance must be fully understood and the threats facing it must be known (6). In November 2002 all seahorses were listed on Appendix II of the Convention on International Trade in Endangered Species (CITES); this means that the massive trade in seahorses must be regulated to ensure that the survival of wild populations is not threatened. However, Indonesia, Japan, Norway and South Korea have opted out of the listing for seahorses (3). The conservation organisation Project Seahorse was set up in 1994 to in response to the massive pressures facing all seahorses around the world (5).

For more information see Project Seahorse:
http://www.projectseahorse.org/

For more on the trade in seahorses see:
http://seahorse.fisheries.ubc.ca/trade.html

• Dorsal fin: the unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans.
• Ovipositor: egg-laying organ in female insects and some other animals consisting of outgrowths of the abdomen (the hind region of the body in insects). The stinging organ and poison sac of worker bees and non-reproductive female wasps is a modified ovipositor.
• Pectoral fins: in fish, the pair of fins that are found one on each side of the body just behind the gills. They are generally used for balancing and braking.
• Pelagic: inhabiting the open oceans.
• Prehensile: capable of grasping.

1. Project seahorse 2003. Hippocampus kuda. In: IUCN 2003. 2003 IUCN Red List of Threatened Species (March 2004): http://www.redlist.org
2. Fishbase- Hippocampus kuda (March 2004): http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=46324&genusname=Hippocampus&speciesname=kuda
3. Project Seahorse- Trade (March 2004): http://seahorse.fisheries.ubc.ca/trade.html
4. Project Seahorse- Biology of seahorses (March 2004): http://seahorse.fisheries.ubc.ca/biology2.html
5. Seahorse Conservation Programme (March 2004): http://www.angleseyseazoo.co.uk/seahorse.htm
6. Project Seahorse- Conservation (March 2004): http://seahorse.fisheries.ubc.ca/conservation.html