A seahorse is any of 46 species of small marine fish in the genus "Hippocampus". Seahorses are mainly found in shallow tropical and temperate salt water throughout the world.

Seahorses range in size from 1.5 to 35.5 cm (5⁄8 to 14 in). They are named for their equine appearance, with bent necks and long snouted heads and a distinctive trunk and tail.

The male seahorse is equipped with a brood pouch on the ventral, or front-facing, side of the tail. When mating, the female seahorse deposits up to 1,500 eggs in the male's pouch. The male carries the eggs for 9 to 45 days until the seahorses emerge fully developed, but very small. The young are then released into the water, and the male often mates again within hours or days during the breeding season.

The number of young released by the male seahorse averages 100–1000 for most species, but may be as low as 5 for the smaller species, or as high as 2,500. When the fry are ready to be born, the male expels them with muscular contractions. He typically gives birth at night and is ready for the next batch of eggs by morning when his mate returns. Like almost all other fish species, seahorses do not nurture their young after birth.

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