Seahorse Biology & Anatomy
Seahorses, and their relatives the seadragons and pipefish, all belong to the family Sygnathidae (pronounced sing-nath-I-dee) from the Greek words syn meaning together and gnathus meaning jaw, which describes the tubular, fused snout that is common among relatives of this family. Seahorses belong to the genus, Hippocampus from the Greek words hippos meaning horse and kampos meaning sea monster.
Seahorses are a fish, being a member of the Teleosts or bony fish group. They have a skeleton made up of bony plates, they use gills to breath and have an inflatable bladder to help regulate their buoyancy in the water. All seahorses are fully marine species, although they can tolerate vast salinity ranges and some live in estuaries; where the salinity fluctuates regularly.
Seahorses are found world-wide, usually in shallow, coastal tropical and temperate waters, there are however some species that are found in water as deep at 60 meters. There are about 50 species of seahorse currently recognized. The greatest number of species is found in the Indo-Pacific region. Australia has at least 14 species and Japan at least 7 species.
The seahorse’s tail is prehensile, and is used to grasp coral, grasses or other holdfasts. Seahorses lack a caudal fin, instead propelling themselves by a dorsal fin located on their back, which beats at around 70 times per minute. There are also two pectoral fins located behind their gills, which help them to maneuver. Seahorses range in size from less than 1 inch for some pygmy seahorse species to 12 inches for the largest seahorse species.
Adult seahorses have few predators due to their bony plating making themselves unpalatable to most fish, and due to their great camouflage. Seahorses can change colors to match their surroundings and grow skin appendages to match algae filaments. Predators include crabs, sharks and rays, and angler fish. They’ve also been found in the bellies of tuna and penguins. Its thought that their number one predator though is man, harvesting millions a year.
In a reversal of sex roles, male seahorses are the ones that have the babies. Females deposit eggs into a special brood pouch the males have at the base of their tale. The male then broods the eggs for 10 – 31 days before releasing hundreds miniature versions of their parents, most under 1cm long.
Seahorse are sexually dimorphic, meaning that the males and females have physical differences. The most obvious difference is that males have a brood pouch at the base of their tail, while the female’s is squared-off where the body meets the tail. However there are a number of other differences. Males have a keel, which is a ridge that runs along the ventral side of their body, much like a boat keel. Males also have a tail that is proportionally much longer than the trunk. Females have longer snouts on average than males. There is also thought to be coloration and pattern differences between the sexes in some species.