Seahorses and pipefishes are notable for being the only species in which males become “pregnant”.
Seahorses are a genus (Hippocampus) of fish belonging to the family Syngnathidae, which also includes pipefish and leafy sea dragons. There are over 32 species of seahorse, mainly found in shallow tropical and temperate waters throughout the world.

Seahorses are unique in appearance, resembling an amalgamation of body parts taken from numerous animals: a horse-like head, a monkey-like prehensile tail, chameleon-like eyes and insect-like body armour, but they are, however a peculiar species of fish equipped with a backbone, (unusual grape-like) gills, swim bladder and fins.

When the female’s eggs reach maturity,they deposit the egg in male brood pouch where the male fertilizes.The fertilized eggs then embed in the pouch wall and become enveloped with tissues.But recent say fertilization occurs outside(I still need to find that article and later update again with correct info.)Male seahorses compete with each other to become pregnant for three weeks (during which time they cannot move around to search for the best food), go through 72 hours of labour and exhausting final contractions to release up to 200 baby seahorses.

The question of why it is the males who undergo pregnancy rather than the females is actually not entirely known.Sea Horses are believed to evolved 40 million years ago with undergoing minimal change in body plan.It resembles a mythological character thats the reason why it attracts artists and poets.

Sex Role Reversal

Since the males sea horses are pregnant, much speculation has been made as to whether or not they are sex role reversed. Sex role reversal involves the female competing for males as a mate. Male parental care is not a determinant in sex role reversal. Research by Vincent and others (1992) has shown that sea horses are not sex role reversed, though several species of pipe fish are. Also, the sea horses demonstrate a monogamous relationship. Males provide parental care for the young. While the young are in the pouch, males give oxygen through a capillary network, transfer nutrients, and change the atmosphere in the pouch. The atmosphere change in the pouch makes the inside of the pouch contain more salt water so the young will be prepared to go into the ocean water when they are born (Vincent, et. al 1997).

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