Biology of sea horses
Sea horses are bony fish (or teleosts) in the family Syngnathidae, which includes about 230 species in 55 genera, most of which are pipefishes. The "true" sea horses comprise some 25 species in the genera Hippocampus and Phyllopteryx, which make up the subfamily Hippocampinae.
Species of sea horses occur in warm-temperate and tropical waters of all of the world's oceans. The usual habitat is near the shore in shallow-water places with seagrass, algae, or corals that provide numerous hiding places for these small, slow-moving fish. Sea horses may also occur in open-water situations, hiding in drifting mats of the floating alga known as sargasso-weed or Sargassum. The lined sea horse (Hippocampus erectus) is one of the more familiar species, occurring on the Atlantic coast of the Americas.
Sea horses have an extremely unusual and distinctive morphology. Their body is long, narrow, segmented, and encased in a series of ring-like, bony plates. Sea horses have a long, tubular snout, tipped by a small, toothless mouth. They have relatively large eyes, and small, circular openings to the gill chamber. The head of sea horses is held at a right angle to the body, and it has a superficial resemblance to that of a horse; hence the common name of these small fish.
Sea horses swim in an erect stance, buoyed in this position by their swim bladder. Sea horses lack pectoral and dorsal fins, but use their anal fin to move in a slow and deliberate manner. Sea horses have a prehensile tail, which is used to anchor the animal to a solid structure to prevent it from drifting about.
Because they are so slow-moving, sea horses are highly vulnerable to predators. To help them deal with this danger, Sea horses are cryptically marked and colored to match their surroundings, and they spend much of their time hiding in quiet places. Sea horses mostly feed on zooplankton and other small creatures, such as fish larvae. The size range of the prey of sea horses is restricted by the small mouth of these animals.
Sea horses take close care of their progeny. The female sea horse has a specialized, penis-like structure that is used to deposit her several hundred eggs into a brood-pouch located on the belly of the male, known as a marsupium. The male secretes sperm into his marsupium, achieving external fertilization of the eggs. The male sea horse then broods the eggs within his pouch until they hatch. Soon afterwards, swimming, independent young are released to live in the external environment.
Because sea horses are such unusual creatures, they are often kept as pets in saltwater aquaria. They are also sometimes dried and sold as souvenirs to tourists. Sea horses for these purposes are captured in the wild. Sea horses are also prized in eastern Asian herbal medicine. Millions of sea horses are caught for these uses each year, particularly the medicinal uses. Unfortunately, the exploitation is much too intense, and is causing the populations of most species to decline precipitously. Consequently, all species of seahorses are considered to be vulnerable to becoming extinct. Regrettably, although their perilous situation is well known, seahorses are not yet being well protected from the over-exploitation.
Scott, W.B., and M.G. Scott. Atlantic Fishes of Canada. Toronto: University of Toronto Press, 1988.
Whiteman, Kate. World Encyclopedia of Fish & Shellfish. New York: Lorenz Books, 2000.