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See a Male Seahorse Give Birth

Unlike almost all other animal species, it is male seahorses who become pregnant and birth young

Korean seahorse

Korean seahorse (Hippocampus haema) releases young into the water off the coast of Japan.


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In all of the vast animal kingdom spanning the planet, seahorses (and their pipefish and sea dragon relatives) are the only species whose male members give birth to young. This underwater photograph shows a male Korean seahorse (Hippocampus haema) releasing juveniles into the water off the coast of Japan. The tiny species, which was only recognized in 2017, generally grows to between about five and nine centimeters long and is native to the Korea Strait and the seas to the east of the Korean peninsula and to the south and west of Japan. After an elaborate courtship “dance,” females deposit their eggs into a male’s brood pouch, where he fertilizes them. As the embryos grow, the male’s abdomen becomes distended, just as in a human pregnancy. When he is ready to give birth, the abdomen opens, and contractions expel the juvenile seahorses. Some newborns resemble miniature versions of adults, while others may still be curled up and covered by some of their egg membrane. A male and female seahorse pair can have multiple broods. It is unknown why seahorses have this sex reversal when it comes to procreation, but one idea is that having the male bear young leaves the female free to start producing the next batch of eggs.

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Andrea Thompson is an associate editor covering the environment, energy and earth sciences. She has been covering these issues for 16 years. Prior to joining Scientific American, she was a senior writer covering climate science at Climate Central and a reporter and editor at Live Science, where she primarily covered earth science and the environment. She has moderated panels, including as part of the United Nations Sustainable Development Media Zone, and appeared in radio and television interviews on major networks. She holds a graduate degree in science, health and environmental reporting from New York University, as well as a B.S. and an M.S. in atmospheric chemistry from the Georgia Institute of Technology.

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