A Seahorse Dad Gives Birth in the Ocean


When it comes to seahorses, the miracle of birth has a twist. Out of the entire animal kingdom, seahorses (and their close relatives, the pipefish and seadragons) are part of an elite group where the males take on the role of pregnancy and birth.

Depicted in this series of images is the cycle of courtship, transfer of eggs from a female to a male, and the birth of tiny Korean seahorses (Hippocampus haema). The species, which is native to the waters of Korea and along the southern and western coasts of Japan, is a relatively recent discovery – officially described for the first time in 2017. There is limited information about this fish, and minimal observation in the wild.

Photographer Tony Wu spent time in June 2020 observing the 8cm tall seahorses, to develop an understanding of their behaviour. He finally felt like he had a good idea on his final night of diving with them: “I will say that it is the first time I have felt fish exhibit affection for one another,” says Wu. “My heart melted as I watched one mating pair interact. I do not have words adequate to describe the intimacy.”

In Japan, the breeding season spans several months, from early spring through summer. The seahorses form pairs through elaborate and beautiful courtship that involves ritualised greetings and swimming patterns that Wu likens to a “dance.” The seahorses maintain eye contact when separated and often intertwine their prehensile tails (behaviours seen in the images below). They seem—for lack of a better description—to exhibit affection.

Getting pregnant

Although male seahorses carry the eggs, they first have to acquire them. The courtship rituals reach their climax when the female deposits her eggs inside the male’s brood pouch. His abdomen becomes distended in readiness for the precious payload, and the male fertilises the eggs inside the pouch. Ta-da! He’s now pregnant, and will carry the developing young for the next three to ten weeks. As for the female, her parental role is now over. It extends no further than provisioning the eggs with nutrient-rich yolks that help feed the developing embryos.

New research published this month by the University of Sydney and La Trobe University in Australia suggests that papa seahorses also provide nutrients to their young in the pouch – most likely in the form of energy-rich fats. Although the babies are not connected to the male’s bloodstream by an umbilical cord, it seems the tissue inside Dad’s brood pouch has at least some capability of delivering oxygen as well, possibly even immunity to protect the growing young from infection. As the embryos grow and take up more room, the male’s pouch begins to swell, much like the belly of a very pregnant human. During this time, the hormone oestrogen is secreted by the male, starting a cascade of genetic signals, which culminate in birth.


The birth itself is a prolonged process. Males seem to prepare their soon-to-be-born young with a series of jerky movements. When the father is ready, he usually seeks relatively high ground in order to cast his babies into the water column. Like human mothers in labour, seahorse dads give birth through a series of muscular spasms. The abdomen opens, and the male undergoes a series of full-body contractions to eject the juveniles. Some emerge in recognisable form. Most catapult into the world still curled-up in the foetal position, partially covered by their egg membrane (barely visible in some of the photos). Some unfurl soon after being ejected. Others sink as they take time to adjust. Brood size depends on the individuals and time of the breeding season, but it can range from several dozen to hundreds.

After hatching the juveniles, the male engages in courtship with the female again, and can bear multiple broods throughout the spring and summer breeding season. The bond between breeding pairs appear to be stable through the season, though there is occasional hanky-panky, notes Wu. “Females sometimes attempt to lure males away from their chosen partner, employing charm and subterfuge to tempt males to accept their eggs (as depicted in one of the photos). Not to be outdone, males sometimes do the same for committed females. But when a male is up to no good, he lacks the subtlety of the fairer sex, preferring to chest thump, body slam and head butt his way towards an egg transfer.”

An Unsolved Mystery

Why male seahorses get pregnant in the first place—when females have this responsibility in almost all other animals—is a mystery yet to be solved. Some scientists theorise that the sex role reversal speeds up the reproduction process, allowing more babies to be born in less time. After all, if the male is bearing the young, the female can start preparing the next batch of eggs.

While seahorse dads go the extra mile to give birth, they offer no parental care to their tiny offspring once they are born. However, the protection the babies receive in Dad’s pouch gives them a strong head start in life. Some 60-70% of all known fish species simply abandon their eggs to the mercy of the ocean after fertilisation, but a seahorse delivers—literally—before sending the kids on their way.