Seahorses (Hippocampus spp of the family Syngnathidae) are fascinating examples of bony fish. They have a unique body morphology with a horse-shaped head, large eyes, curved trunk, and a prehensile tail. Even though these charismatic creatures are banned as trade items, they are still heavily traded in the illicit international markets.

Fast Facts: Seahorses Scientific Name: Syngnathidae (Hippocampus spp)

Syngnathidae (Hippocampus spp) Common Name: Seahorse

Seahorse Basic Animal Group: Fish

Fish Size: 1–14 inches

1–14 inches Lifespan: 1–4 years

1–4 years Diet: Carnivore

Carnivore Habitat: Temporal and tropical waters throughout the world

Temporal and tropical waters throughout the world Conservation Status: Not Evaluated

Description

After much debate over the years, scientists finally decided that seahorses are fish. They breathe using gills, have a swim bladder to control their buoyancy, and are classified in the Class Actinopterygii, the bony fish, which also includes larger fish such as cod and tuna. Seahorses have interlocking plates on the outsides of their bodies, and this covers a spine made of bone. While they have no tail fins, they have four other fins—one at the base of the tail, one under the belly, and one behind each cheek.

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Some seahorses, like the common pygmy seahorse, have shapes, sizes, and colors that allow them to blend in with their coral habitats. Others, such as the thorny seahorse, change color to blend in with their surroundings.

According to the World Register of Marine Species, there are 53 species of seahorses (Hippocampus spp), though other sources number the existing species between 45 and 55. The taxonomy has proven difficult because seahorses don't vary a great deal from one species to another. They do, however, vary within the same species: Seahorses can and do change color and grow and lose skin filaments. Their size ranges from under 1 inch to 14 inches long. Seahorses are categorized in the family Syngnathidae, which includes pipefish and seadragons.

Habitat and Range

Seahorses are found in temperate and tropical waters throughout the world. Favorite seahorse habitats are coral reefs, seagrass beds, estuaries, and mangrove forests. Seahorses use their prehensile tails to anchor themselves to objects such as seaweed and branching corals.

Despite their tendency to live in fairly shallow waters, seahorses are difficult to see in the wild, since they can remain very still and blend in with their surroundings.

Diet and Behavior

Although there is some variation based on species, in general, seahorses feed on plankton and tiny crustaceans such as amphipods, decapods, and mysids, as well as algae. Seahorses do not have stomachs, so food passes through their bodies very quickly, and they need to eat often, between 30 and 50 times a day.

Although they are fish, seahorses are not great swimmers. Seahorses prefer to rest in one area, sometimes holding on to the same coral or seaweed for days. They beat their fins very quickly, up to 50 times a second, but they do not move quickly. They are able to move up, down, forward or backward.

Reproduction and Offspring

Many seahorses are monogamous, at least during a single breeding cycle. A myth perpetuates that seahorses mate for life, but this doesn't seem to be true.

Unlike many other fish species, though, seahorses have a complex courtship ritual and may form a bond that lasts during the entire breeding season. The courtship involves an enchanting "dance" in which they entwine their tails​ and may change colors. Larger individuals—male and female both—produce larger and more offspring, and there is some evidence for mate choice based on size.

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Unlike any other species, male seahorses become pregnant and carry babies (called fry) to term. Females insert their eggs through an oviduct into the male's brood pouch. The male wiggles to get the eggs into position, and once all the eggs are inserted, the male goes to a nearby coral or seaweed and grabs on with his tail to wait out gestation, which lasts 9–45 days.

Males produce 100–300 young per pregnancy and while the main source of food to the embryos is the yolk of the egg, the males do provide additional sustenance. When it's time to give birth, he'll contort his body in contractions until the young are born, over a period of minutes or sometimes hours.

Conservation Status

The International Union for Conservation of Nature (IUCN) has not as yet evaluated seahorse endangerment, but Hippocampus spp were among the first fishes brought under global trade restrictions in 1975. They are currently listed in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), which allows exports of specimens only if they are sourced sustainably and legally.

All countries which were historically exporting large numbers of them have since banned the export or are under CITES export suspensions—some banned the export prior to 1975.

Nevertheless, seahorses are still threatened by harvesting for use in aquariums, as curios, and in traditional Chinese medicine. Historic and recent fisheries and/or trade surveys in source countries with trade bans have all revealed persistent exports of dried seahorses through unofficial channels. Other threats include habitat destruction and pollution. Because they are hard to find in the wild, population sizes may not be well-known for many species.

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Seahorses and Humans

Seahorses have been a topic of fascination for artists for centuries, and are still used in Asian traditional medicine. They are also kept in aquariums, although more aquarists are getting their seahorses from "seahorse ranches" now rather than from the wild.

Author and marine biologist Helen Scales, Ph.D., said of seahorses in her book "Poseidon's Steed": "They remind us that we rely on the seas not only to fill our dinner plates but also to feed our imaginations."