Seahorses and their relatives the pipefishes belong to the fish family Syngnathidae. These fishes have highly-modified bodies. Their scales are replaced by a series of jointed bony rings that encircle the flexible tail and interlocking plates that cover the rigid body.

Seahorses, named for their loose resemblance to horses, are actually weak swimmers that hover or glide slowly from place to place by undulating the small dorsal and pectoral fins; their pelvic fins as well as a true tail fin. Their unusual posture — with head up and tail down — contributes to their equine look. Seahorses live and move at right angles compared to most fishes and often maintain position by holding onto seaweed or other objects with their flexible tail. The long, tubular jaw is adapted for sucking small crustacean plankton from the water.

Seahorses and most of their kin are best known for their unusual reproductive pattern. Males have a special patch or pouch on the belly surface that provides incubation for the female’s eggs. A female and male engage in daily “bonding” activities, swimming together each morning, side by side with their tails entwined. Then, in a pairing unlike most marine fishes, female seahorses deposit their eggs into a brood pouch on the males’ abdomen where they are fertilized. The developing embryos spend one to three weeks in the protection of the pouch. When development is complete, the quarter-inch young are expelled, looking like miniature versions of the adults. There is no larval stage as in most marine fishes, but there is a short pelagic stage before they settle into the benthic environment.

Seahorse populations are threatened by heavy harvesting for markets in dried seahorse trade and due to accidental fisheries by-catch. The aquarium hobby trade accounts for about 4% of the seahorse harvest, but efforts by aquariums and other institutions are involved in developing reliable rearing techniques that provide alternatives to collecting seahorses from the wild.