Seahorses are a genus (Hippocampus
) of fish belonging to the family Syngnathidae, which also includes pipefish and leafy sea dragons. The seahorses are found in tropical and subtropical coastal and reef waters all over Pacific, Atlantic and Indian oceans.
Seahorses range in size from 16 mm (the recently discovered Hippocampus denise
) to 350 mm. Seahorses and pipefishes are notable for being the only species in which males become "pregnant".
The seahorse has a dorsal fin located on the lower body and pectoral fins located on the head near their gills.
Sea dragons are close relatives of seahorses but have bigger bodies and leaf-like appendages which enable them to hide among floating seaweed or kelp beds. Seahorses and sea dragons feed on larval fishes and amphipods, such as small shrimp-like crustaceans called mysids ("opossum shrimp"), sucking up their prey with their small mouths. Many of these amphipods feed on red algae that thrives in the shade of the kelp forests where the sea dragons live.
Seahorses reproduce in an unusual way: the male becomes pregnant. "The female inserts her ovipositor into the male’s brood pouch, where she deposits her eggs, which the male fertilizes. The fertilized eggs then embed in the pouch wall and become enveloped with tissues." New research indicates the male releases sperm into the surrounding sea water during fertilization, and not directly into the pouch as was previously thought. Most seahorse species' pregnancies lasts approximately two to three weeks.
Hatched offspring are independent of their parents. Some spend time developing among the ocean plankton. At times, the male seahorse may try to consume some of the previously released offspring. Other species (H. zosterae) immediately begin life as sea-floor inhabitants (benthos).
Seahorses are generally monogamous, though several species (H. abdominalis among them) are highly gregarious. In monogamous pairs, the male and female will greet one another with courtship displays in the morning and sometimes in the evening to reinforce their pair bond. They spend the rest of the day separate from each other hunting for food.
While many aquarium hobbyists will keep seahorses as pets, seahorses collected from the wild tend to fare poorly in a home aquarium. They will eat only live foods such as brine shrimp and are prone to stress in an aquarium, which lowers the efficiency of their immune systems and makes them susceptible to disease.
In recent years, however, captive breeding of seahorses has become increasingly widespread. These seahorses survive better in captivity, and they are less likely to carry diseases. These seahorses will eat mysid shrimp, and they do not experience the shock and stress of being taken out of the wild and placed in a small aquarium. Although captive-bred seahorses are more expensive, they survive better than wild seahorses, and take no toll on wild populations.
Seahorses should be kept in an aquarium to themselves, or with compatible tank-mates. Seahorses are slow feeders, and in an aquarium with fast, aggressive feeders, the seahorses will be edged out in the competition for food. Special care should be given to ensure that all individuals obtain enough food at feeding times.
Seahorses can co-exist with many species of shrimp and other bottom-feeding creatures. Fish from the goby family also make good tank-mates. Some species are especially dangerous to the slow-moving seahorses and should be avoided completely: eels, tangs, triggerfish, squid, octopus, and sea anemones.
Animals sold as "freshwater seahorses" are usually the closely related pipefish, of which a few species live in the lower reaches of rivers. The supposed true "freshwater seahorse" called Hippocampus aimei was not a real species, but a name sometimes used for individuals of Barbour's seahorse and Hedgehog seahorse. The latter is a species commonly found in brackish waters, but not actually a freshwater fish.
Use in Chinese medicine
Seahorse populations have been endangered in recent years by overfishing. Therefore, seahorse fishing is strictly illegal. The seahorse is used in traditional Chinese herbology, and as many as 20 million seahorses may be caught each year and sold for this purpose. Medicinal seahorses are not readily bred in captivity as they are susceptible to disease and have somewhat different energetics than aquarium seahorses.
Import and export of seahorses has been controlled under CITES since May 15, 2004.
The problem may be exacerbated by the growth of pills and capsules as the preferred method of ingesting medication as they are cheaper and more available than traditional, individually tailored prescriptions of raw medicinals but the contents are harder to track. Seahorses once had to be of a certain size and quality before they were accepted by TCM practitioners and consumers. But declining availability of the preferred large, pale and smooth seahorses has been offset by the shift towards prepackaged medicines, which make it possible for TCM merchants to sell previously unused juvenile, spiny and dark-coloured animals. Today almost a third of the seahorses sold in China are prepackaged. This adds to the pressure on the species.
A seahorse has highly mobile eyes to watch for predators and prey without moving its body. Like the leafy sea dragon, it also has a long snout with which it sucks up its prey. Its fins are small because it must move through thick water vegetation. The seahorse has a long, prehensile tail which it will curl around any support such as seaweed to prevent being swept away by currents.
[List of Seahorse Species