Seahorses are amazing and unique in many ways. Even though they are fish, they have the shape of a horse and are monogamous. Most surprisingly, the male carries the unborn baby throughout gestation. How does this happen? And how do seahorses give birth? We will explain.
During courtship, the female seahorse produces eggs. When the eggs reach maturity, she will deliver them into the male’s pouch using her ovipositor. Then the male will fertilize them with its sperm internally and carry them for about twenty days. When the baby seahorses have fully developed from the egg, he will forcefully eject them into the water.
That sounds fantastic and unusual, right? But there is still more to the reproductive mechanism. Let’s discuss it in detail.
Courtship and Copulation (the act of mating) in Seahorses
Most species of seahorses are monogamous. They usually have permanent mate partners, at least during a breeding season.
However, some occasionally break this rule (tisk tisk…). Copulation in seahorses usually involves a long process that may take days.
It starts from courtship in which the pair dance together in the water. This may take several days and involves different stages. They may also change color in the process.
The courtship usually takes place in four stages. The intensity of their behavior and color changes increases from phase one to phase four before the real copulation takes place. During these stages, they will swim side by side, show body vibration, exhibit pointing behavior, and wheel around together.
The final stage of courtship will see the pair anchored to a plant at the waterbed. From that position, they will rise together in a column of water. During this time, the male will show his partner his empty pouch. It will pump water into it to make it clearly visible. The pouch is located at the ventral side of the male seahorse’s tail, and its main purpose is to keep the egg and carry the young ones until they have fully developed.
When the female is ready to deposit her egg, the pair will let go of the grass they are clinging to and rise in the water.
Then the pair will physically copulate, during which the female seahorse will insert her ovipositor into the male pouch and deposit her eggs.
The egg may be anything from a few tens to thousands. The average number is around 1000 eggs. After the eggs had been transferred, both will return to the seagrass and then separate. The female usually swims away.
However, after transferring the eggs they need to be fertilized and incubated before they can develop into young seahorses. How does this happen?
Gestation (Conception)
Fertilization in seahorses is internal. The male produces sperms and uses them to fertilize all the eggs.
During copulation, some water will enter the pouch. This water will aid the motility of the sperm. Once the eggs are fertilized, they will attach themselves to the walls of the pouch.”
The wall of the pouch will provide oxygen and warmth for the embryo, while the egg yolk will provide nourishment.
Prolactin will also be produced to strengthen the embryo. The male will also supply additional nourishment. He will carry the eggs between 9 to 45 days, with the average gestation period being around 14 to 28 days.
Humorously, throughout this period, the female seahorse will visit every morning just to greet. This is probably to increase their bond.
When the embryos have fully developed into young seahorses, they will hatch and ready to leave the pouch for a separate life in water.
Then, the male’s muscles will contract, which will force the young fish to be expelled from his pouch into the water.” The fries (babies) are left to fend for themselves afterward. This usually takes place at night, and by the morning, the male seahorse is ready to mate again.
Why the Males are the Ones Carrying the Fertilized Eggs
Seahorses are among the few species of animals in which it is the male that carries unborn babies.
In most species of organism, it is the females that usually carry the pregnancy or fertilized eggs. In beds where fertilization is external, it is still the female that normally incubates the eggs till they are hatched. But in seahorses, the role is reversed. What could be responsible for this?
Scientists believe that transferring the role to the male helps balance the energy expenditure during reproduction.
Research showed that a lot of energy is needed to generate the eggs. In fact, the energy needed to generate the eggs is more than the energy needed to carry them to maturity.
Despite the male carrying the fertilized eggs, the entire process still costs the female more energy than the male. Hence, if both roles are given to the female, the burden would have been too much for her. This is why it must be shared, with the male taking up the lesser role.
Another factor that may be responsible for the incubation role of the male seahorse is the need to produce as much offspring as possible. As there is no parental care for the young ones, it is estimated that only 5 percent of the offspring of a seahorse will survive to adulthood.
Therefore, there is a need to reproduce as often as possible. Egg production takes a significant time. This time will be further prolonged if the female still has to carry the eggs after fertilization. But by depositing them into the male, the female can start producing another set of eggs.
Summary
Every male seahorse has a pouch in its ventral part of the tail. The fish uses the pouch to carry eggs and incubate them in its body.
Seahorses reproduce by the female depositing eggs into the male pouch of the male during copulation.
The male will mix the eggs with sperm to fertilize them. After fertilization, the eggs will remain in the pouch until they are hatched into small fish. Then the male will forcefully eject them from its body. Another round of the reproduction cycle may start immediately.
