Seahorses | National Geographic (2024)

What are seahorses?

The oddly shaped and upright-swimming seahorse seems an unlikely fish. Yet more than 45 species live in coastal waters around the globe. Scientists have learned their basic biology, but much remains unknown about these charismatic animals.

Physical description

Its head may resemble a horse’s, but each seahorse has a look all its own. Most are spotted, speckled, or striped, and some are decked out in skin frills, spikes, and crowns. Colors vary and can change with the twitch of a muscle to offer camouflage or to signal a foe or potential mate.

Seahorses have flesh-covered bony plates instead of scales, eyes that work independently of each other, and prehensile tails—used to grip holdfasts on the seafloor to avoid drifting and, during courtship, to link to each other.

The tiniest species is no bigger than a lima bean; the largest can reach more than a foot from head to tail tip.

Habitat and movement

Preferring calm, shallow waters, seahorses thrive in seagrass beds, mangroves, estuaries, and coral reefs in temperate and tropical waters around the world. Relatively inept swimmers, the fish get around with frantic beats (up to 70 times per second) of a dorsal (back) fin and rely on tiny pectoral fins for stability and steering. Easily exhausted, many are swept away in heavy currents or killed in storm-roiled seas.

Diet

Seahorses are ambush predators: They hold still and wait for krill, copepods, fish larvae, and other tiny edibles to float by and then nab them with remarkable speed. Toothless and lacking a stomach for food storage, the animals use their long snouts like vacuum cleaners to suck up plankton nearly continually.

Courtship

Seahorses are dancers at heart, circling one another or a floating object, flashing colors, and intertwining tails during a sometimes days-long courtship. Said to mate for life, a pair’s commitment may actually be fragile: If the two are separated for a time, or if the male’s health declines, a female may switch partners rather than stick with her original choice.

Reproduction

In a reproductive role reversal unique to seahorses and others in the family Syngnathidae (which also includes pipefish and sea dragons), males experience pregnancy. During mating a female uses a tube called an “ovipositor” to place her eggs into the male’s frontal “brood pouch.” He then incubates, nourishes, and carries the young to term—usually two to four weeks. With powerful contractions he’ll give birth to fully developed fry, from dozens to more than a thousand depending on the species. Newborn seahorses, set adrift, are immediately vulnerable to predators, and few survive their early days.

Threats

Pollution and coastal development harm seahorses, but the top threat is rampant overfishing. Commercial fishermen scoop up millions of seahorses a year as bycatch. There is also targeted fishing of seahorses to supply tourist demand for dried trinkets and an unregulated traditional-medicine market in Asia.

Population data for many seahorse species is sparse, but scientists believe the vast majority are threatened and some populations in rapid decline. How warming seas due to climate change will affect seahorses long term is unknown.

Saving seahorses

Protecting seahorses will require protecting their shallow-water habitats from pollution and destructive development, enforcing commercial-fishing laws aimed at stemming the bycatch problem, and reducing demand for these animals as trinkets and supposed medicinal supplements.