A relatively large species, the common seahorse (Hippocampus kuda) is unfortunately not as common as its name suggests, and is considered Vulnerable by the IUCN (1). Like all seahorses, the head of the common seahorse 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 the seahorse steers 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).
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, when the female inserts her ovipositor into the male’s pouch and lays her eggs. The male then fertilises the eggs, which 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).
Like other seahorses, the common seahorse is an ambush predator, and lies in wait for small crustaceans to swim by; it then sucks the prey into the tube-like mouth and swallows it whole, as it does not have any teeth (5). Seahorses 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).
The common seahorse is found throughout South East Asia, Australia, Japan and some Pacific islands (including Hawaii) (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).
This species typically inhabits shallow waters, in estuaries, reefs and on mud slopes where there is seagrass or marine algae. The common seahorse has also been found in open water and attached to drifting vegetation up to 20 kilometres off shore (2).
The common seahorse 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) (6). Furthermore, habitat degradation and pollution in some areas reduces the available habitat for the common seahorse, and it is also often accidentally caught as bycatch in the shrimp-trawling industry (1).
The most pressing requirement to assist in the conservation of the common seahorse 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 (7). 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 (3). However, Indonesia, Japan, Norway and South Korea have opted out of the listing for seahorses (6). The conservation organisation Project Seahorse was set up in 1994 in response to the massive pressures facing all seahorses around the world (5).
To learn more about a Whitley Award-winning conservation project for this species, click here.
Simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.
In the fishing industry, the part of the catch made up of non-target species.
Diverse group of arthropods (a phylum of animals with jointed limbs and a hard chitinous exoskeleton) characterised by the possession of two pairs of antennae, one pair of mandibles (parts of the mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, woodlice and barnacles.
The unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans.
The fusion of gametes (male and female reproductive cells) to produce an embryo, which grows into a new individual.
Egg-laying organ in female insects and some other animals consisting of outgrowths of the abdomen (the hind region of the body in insects).
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.
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