Ever wonder how the world might be different if men gave birth? Taking a peek at the lifestyle of a seahorse may give you an idea – the male seahorse not only fertilizes the eggs of a female, but he carries them to term and gives birth.

Because they supply the sperm to fertilize the eggs, pregnant seahorses are undeniably male. Only a mammalian chauvinist would suggest otherwise. Here’s how it works in the world of seahorses:

At dawn, the male greets the female by quivering to get her attention. He demonstrates his masculinity by puffing out a brood pouch located on his belly. The female signals she is ready by quivering. The couple dance around one another, holding each other’s tails and pirouetting for up to 10 minutes.

During the dance, the female deposits her eggs into the male’s brood pouch, which then seals over with tissue. The male’s sperm fertilizes the eggs, and the embryos begin to grow within the pouch.

The pouch becomes, for all intents and purposes, a womb. Capillaries in the pouch deliver oxygen and other nutrients just as an umbilical cord would. Hormones within the male spur the creation of placental fluid, which gradually changes from bodily fluid to fluid similar to the surrounding water. This helps reduce stress on the young at birth.

The male carries the little bundles of joy for about a month, though some species, such as the Hippocampus zosterae or dwarf seahorse, will give birth in just 15 days. The father keeps the young safe in his pouch until they reach an advanced stage of development. In fact, the fry can take care of themselves immediately upon birth. Meanwhile, the male cannot reproduce until the fry are born.

When he’s ready to give birth, the father goes into labor. He becomes agitated and begins contracting and jackknifing to eject the young from the pouch. The fry are small replicas of the parents, ranging in size from 7 to 11 millimeters in length. They go off immediately into the world to make their parents proud by finding a suitable mate to produce more fry.

Fortunately for seahorses, they don’t have to worry about buying dad a Father’s Day gift – imagine how difficult that would be.

Seahorses, by the way, are fish that swim upright. They are classified in the same family as the pipefish, sea dragon and pipe horses (Syngnathidae), the only family of vertebrates known in which the males becomes pregnant. Unlike most fish, they don’t have scales; the skin is stretched over a series of bone plates. They range in size from less than an inch (10 to 20 millimeters) to more than a foot (300 mm). Their lifespan lasts between a year and four years, depending on the species.

Bringing Up Father

So what effect does this reversal of the traditional roles have on seahorse society? Well, unlike much of the animal kingdom, the male cannot reproduce at will; he must wait until after each birth to pass on his genetic material again. This limits his chances of reproduction, which is unusual for male fish.

Although the male gives birth, he still must attract the female by showing off his pouch and healthy colors. Once he finds his partner, though, the relationship is usually monogamous throughout their lives. Scientists suspect that males bond strongly with females because they cannot mate and then merrily leave to mate again with another female. Fortunately for the male, the female is also very devoted.

The bonding is so strong that if one seahorse is lost or dies, the other is slow to find another mate. After giving birth, the male will begin the courtship ritual again, which can last up to 9 hours until the couple mates again.

To learn more about seahorses and their suitability in a home aquarium, see the story Choosing a Seahorse.