Special Feeding Adaptations of the Seahorse

The seahorse is one of 54 different species of fish in the marine genus Hippocampus—a word that comes from the Greek word for "horse." Only a small handful of species are commonly seen in tropical and temperate waters of both the Pacific and Atlantic Oceans. They range in size from tiny, 1/2-inch fish to nearly 14 inches in length. Seahorses are one of the only fish that swim in an upright position and are the slowest-swimming of all fishes. Seahorses are generally considered to be an evolved form of pipefish.

How Seahorses Eat

Because they swim so slowly, eating can be a challenge for the seahorse. Further complicating things is the fact that a seahorse has no stomach. It needs to eat almost constantly because food quickly passes straight through its digestive system. An adult seahorse will eat 30 to 50 times per day, while baby seahorses eat 3,000 pieces of food per day.

Seahorses do not have teeth; they suck in their food and swallow it whole. Thus their prey needs to be very small. Primarily, seahorses feed on plankton, small fish and small crustaceans, such as shrimp and copepods.

To compensate for its lack of swimming speed, a seahorse's neck is well adapted for catching prey. Seahorses ambush their prey by hovering silently nearby, attached to plants or corals and often camouflaged to blend in with their surroundings. Suddenly, the seahorse will tilt its head and slurp in its prey. This movement results in a distinctive sound.

Unlike their relatives, the pipefish, seahorses can extend their heads forward, a process that is aided by their curving neck. Although they can't swim as well as pipefish, The seahorse has the ability to stealthily reach out and strike their prey. This means that they can wait for prey to pass by their perch, rather than actively pursuing them—a task that is difficult given their very slow speed. The hunt for prey is also aided by the seahorse's eyes, which have evolved to move independently, allowing them an easier search for prey. 

Seahorses as Aquarium Specimens

What about captive seahorses? Seahorses are popular in the aquarium trade, and there is currently a movement to raise seahorses in captivity to protect the wild population. With coral reefs in danger, the native habitat of the seahorse is also challenged, leading to ethical concerns about harvesting them from the wild for the aquarium trade. Further, captive-bred seahorses seem to thrive better in aquariums than do capture wild seahorses. 

However, efforts to breed seahorses in captivity is somewhat complicated by the fact that young seahorses prefer live food that must be very small, given the tiny size of the young seahorses. While they are often fed frozen crustaceans, captive seahorses do better when feeding on live food. Live wild- or captive-raised copepods (tiny crustaceans) and rotifers are a good food source that allows young seahorses to thrive in captivity.

Resources and Further Reading

• Bai, Nina. “How the Sea Horse Got Its Curves.” Scientific American, Springer Nature, 1 Feb. 2011.
• Scales, Helen. Poseidon's Steed: The Story of Seahorses, from Myth to Reality. Gotham, 2009.
• “Sea Horse Facts.” The Seahorse Trust, Seahorse Alliance, 2019.
• Souza-Santos, Lília P., et al. “Prey Selection of Juvenile Seahorse Hippocampus Reidi.” Aquaculture, vol. 404-405, 10 Aug. 2013, pp. 35-40.
• “There's Something About Seahorses.” Birch Aquarium at Scripps Institution of Oceanography, University of California San Diego.