Seahorses and their close relatives,
Although seahorses are the only fish that experience true male pregnancy, the males of two close relatives, sea dragons and pipefish, carry eggs attached to an area beneath their tails.
In seahorses and pipefish, it is the male that gets pregnant and gives birth. Seahorse fathers incubate their developing embryos in a pouch located on their tail. The pouch is the equivalent of the uterus of female mammals. It contains a placenta, supporting the growth and development of baby seahorses.
After he has given birth, the seahorse dad does nothing more for his babies. They must look after themselves and hide from predators, as they have no parents to protect them. The seahorse father does not eat until several hours after he has given birth.
Seahorses and their close relatives, sea dragons, are the only species in which the male gets pregnant and gives birth. Male seahorses and sea dragons get pregnant and bear young—a unique adaptation in the animal kingdom.
Male Seahorses Get Pregnant and Give Birth
After the male and female seahorses spend time courting, the female deposits her eggs inside the male's pouch. The male then fertilizes the eggs inside the pouch. Instead of growing their babies inside a uterus like human moms do, seahorse dads carry their babies in a pouch.
A pregnant dad gestating up to 1,000 babies
This organ is called the brood pouch, in which the embryos develop. The female deposits eggs into the male's pouch after a mating dance and pregnancy lasts about 30 days.
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.
Males produce the sperm (the smallest gametes) and females produce the eggs (the biggest gametes). But in seahorses, the sperm-producers are also the ones that get pregnant.
The gastric-brooding frog is the only known frog to give birth through its mouth. According to researchers at the University of South Wales, the frog lays eggs but then swallows them.
Most animals that procreate through parthenogenesis are small invertebrates such as bees, wasps, ants, and aphids, which can alternate between sexual and asexual reproduction. Parthenogenesis has been observed in more than 80 vertebrate species, about half of which are fish or lizards.
So, the animals, reproducing the babies of their own kind, by directly giving birth, are called mammals. For example, human beings are mammals. Cats, dogs, cows, horses, elephants, goats, pigs, lions, rats, squirrel etc.
Clown fish begin life as males, then change into females, and kobudai do the opposite. Some species, including gobies, can change sex back and forth. The transformation may be triggered by age, size, or social status.
The deep-sea anglerfishes' mating ritual goes something like this: Boy meets girl, boy bites girl, boy's mouth fuses to girl's body, boy lives the rest of his life attached to girl sharing her blood and supplying her with sperm. Ah, a tale as old as time.
By human standards, seahorse courtship is viewed as very romantic. They are monogamous with one partner for their whole lives. Every day they meet in the male's territory and perform a sort of dance where they may circle each other or an object, change colour, and even hold tails.
Most Seahorses are bisexual
Seahorses already defy gender roles, with the males bearing eggs and giving birth to their young, but it also turns out almost all seahorses are bisexual, forming relationships with both male and female partners.
The seahorse has an unusual method of reproduction. In seahorses and pipefish, it is the male that gets pregnant and gives birth. Seahorse fathers incubate their developing embryos in a pouch located on their tail. The pouch is the equivalent of the uterus of female mammals.
Unlike most animals, it is the male seahorse that gives birth. A female seahorse places up to 2,000 eggs inside a pouch on the male's abdomen. The eggs grow there for two to four weeks. As the eggs develop, the father barely moves.
How long do they live? The natural lifespans of seahorses are virtually unknown, with most estimates coming from captive observations. Known lifespans for seahorse species range from about one year in the smallest species to an average of three to five years for the larger species.
Ripe seahorse eggs are usually orange, pear-shaped, and about a tenth of an inch in diameter. Larger females have larger eggs, which usually become larger young. Since in most fish species larger young have higher survival rates, I suspect that male seahorses prefer larger females, although I have not yet tested this.
Seahorses and pipefish are in the same family and both species have males become pregnant. However, seahorses trump pipefish in the fight for Ocean Father of the Year because of their commitment to monogamy—once the males are pregnant, they will carry their young until they're ready to hatch.