Male pregnancy

Male pregnancy is the incubation of one or more embryos or fetuses by male members of some species. In nearly all heterogamous animal species, offspring are ordinarily carried by the female until birth, but in fish of the Syngnathidae family (pipefish, seahorses and the leafy seadragon), males perform this function. There are different ideas concerning whether a human male could become pregnant, and, by some definitions of gender identity, human men have become pregnant. Male humans incubating fetuses are also a recurring theme in speculative fiction.

The Syngnathidae family of fish has the unique characteristic of a highly derived form of male brood care referred to as "male pregnancy". The family is highly diverse, containing around 300 different species of fish. Included in Syngnathidae are seahorses, the pipefish, and the weedy and leafy seadragons. The males of some of these species possess a brood pouch on the trunk or tail; in other species, the eggs are merely attached to the male's trunk or tail when the female lays them. Although biologists' definitions of pregnancy differ somewhat, all members of the family are considered by ichthyologists to display male pregnancy, even those without an external brood pouch.

Fertilization may take place in the pouch or in the water before implantation, but in either case, syngnathids' male pregnancy ensures them complete confidence of paternity. After implantation in or on the brood pouch or brood patch, the male incubates the eggs. Many species osmoregulate the brood pouch fluid to maintain proper pH for the developing embryos. In at least some species, the male also provisions his offspring with nutrients such as glucose and amino acids through the highly vascularized attachment sites in or on his body.

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