Softly, with a nearly imperceptible rocking motion, seahorses ride the gentle reef currents, drifting from one coral head to another, or attaching themselves to sea fans waving in the liquid breeze. Appropriately named, seahorses are actually nothing more than upright swimming fish, classified among the bony fishes (teleosts), which includes most of the living fish species today. Their unique appearance and graceful style attract aquarists and under the best circumstances they can thrive in a well-established reef tank.
Seahorses are classified in the same family as pipefishes, sea dragons and pipe horses (Syngnathidae), the only family of vertebrates known in which the males – not the females – become pregnant. And if that isn’t odd enough, almost all species of seahorses are strictly monogamous, with a courtship and mating ritual that could be described as tender or even loving. A seahorse couple mates repeatedly and exclusively within and between the reproductive seasons. Throughout their life together, the pair reinforce their bond with elaborate greeting dances performed daily soon after dawn. The female swims to the male and both change color, promenading and pirouetting for several minutes. They then separate for the rest of the day.
When her eggs have developed, the female lays them at the entry of special brood pouches found on the male’s belly. The pouch seals shut and the pregnant male then fertilizes the eggs. He keeps them in his pouch until they’ve reached a relatively advanced stage of development. When the male is ready to give birth, contractions and jack-knife contortions eject the live young from the safety of their father’s pouch. The fry are miniature replicas of their parents, ranging in size from only 7 to 11 millimeters in length, but yet are fully independent from the moment of birth.
The morning after the male gives birth, the usual female greeting is intensified, becoming a full courtship that can last up to nine hours in which the couple mates again. Throughout their partnership, the couple ignore all other seahorses. Should their mate disappear, they are slow to seek a new partner.
Thirty Species of Seahorses
Only thirty species of seahorses are known, all classified into a single genus, Hippocampus, a Greek word meaning “bent horse.” They are found mainly in temperate and tropical waters (usually between 45 degrees N and S latitude), favoring coral reef, mangrove, sea grass and estuarine habitats. Their size can range anywhere from 20 millimeters (less than an inch), as in the newly discovered Australian species, Hippocampus minotaur, to 30 centimeters (over a foot) as in the large Pacific seahorse, Hippocampus ingens. The lifespan of these fish, of which little is known, is thought to range from about one year for smaller species to about four years for medium-sized and larger species.
Seahorses have eyes that move independently of each other, making it easier to spot their prey of small crustaceans (brine shrimp) and plankton, which they suck into their tube-like mouth with a rapid snap of their head. Having no stomachs, these creatures have voracious appetites to satisfy their inefficient digestive system. In the aquarium it is hard to get them to eat anything but live food.
Seahorses don’t have scales like other fish, but rather skin stretched over a series of bony plates, giving the belly and trunk its ringed appearance. Although most seahorses have a natural brownish, beige or even black color to match their surroundings, they change color during greetings and courtship, and also to hide from predators. Depending on the species, some seahorses can make themselves fluorescent orange to deep purple.
Seahorses Are Difficult to Raise in Aquarium
Before acquiring seahorses for your aquarium, consider that they are delicate and their numbers have been severely depleted by over-harvesting for traditional medical use in Asia, by being what fishermen call by-catch. These “extra” fish are caught in nets but have no economic value, and are finally taken by the aquarium trade. They are classified as “vulnerable,” on the IUCN’s Red List of Threatened Animals.
Because of the declining seahorse population and because these fish are so difficult to rear and care for in captivity, only experienced aquarists should undertake keeping them. Virtually all seahorses in pet stores have been caught in the wild. While efforts are underway to create seahorse farming and aquaculture in Southeast Asia, these are only small operations and not yet producing large numbers of the animals.
If you decide you are ready to keep seahorses, make certain you determine which species you will be getting in order to match its habitat needs. The tank needs to be large, at least 25 gallons. You must also be able to provide live food – artemia and ghost shrimp – a least twice a day. If you keep them well, you’ll be rewarded with a truly unique aquarium experience, a chance to see them breed, and the extraordinary sight of the birth of their young.
Before you begin, go to www.projectseahorse.org the site of The Seahorse Project, the work of scientists who study seahorses and work for their conservation. If you raise or keep seahorses, they are interested in hearing from you.