Temporal range: Lower Miocene to Present
Seahorses are a type of teleost fish. They are in the genus Hippocampus. They are called 'seahorses' because their head looks like a horse's head. There are about 32–48 species of seahorse. Seahorses live in tropical oceans.
Seahorses are unique because the male hatches the eggs in a pouch on his belly. The female inserts her ovipositor into the male’s brood pouch. She places dozens to thousands of eggs in the pouch. As the female releases her eggs, her body slims while his swells. The male releases his sperm directly into the water. The sperm then fertilize the eggs in the pouch. The fertilised eggs are then embedded in the pouch wall. They get nutrition and oxygen from the fluid in the pouch. In the pouch, the salinity of the water is controlled. This prepares the newborns for life in the sea.
Throughout gestation, which in most species requires two to four weeks, his mate visits him daily for 'morning greetings'. They interact for about 6 minutes. The female then swims away until the next morning, and the male vacuums up food through his snout.
The number of young released by the male seahorse averages 100-200 for most species, but may be as low as 5 for the smaller species, or as high as 1,500.
When the fry are ready to be born, the male expels them with muscular contractions. He 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 take care of their young after birth. Infants are susceptible to predators or ocean currents which wash them away from feeding grounds or into temperatures too extreme for their bodies. Fewer than 0.5% of infants survive to adulthood. This is why litters are so large. These survival rates are actually fairly high compared to other fish, because of their protected gestation. This makes the process worth the cost to the father. The eggs of most other fish are abandoned immediately after fertilization.
Seahorses are the only fish that experience true male pregnancy. 
- The Seahorse Project
- Milius, Susan (2000). "Pregnant—and Still Macho - seahorses | Science News | Find Articles at BNET.com". Findarticles.com. Retrieved 2009-11-11.
- "Seahorse fathers take reins in childbirth". News.nationalgeographic.com. Retrieved 2009-11-11.
- Connor, Steve (2007-01-19). "Sex and the seahorse - Science, News - Independent.co.uk". London: News.independent.co.uk. Retrieved 2009-11-11.