Male seahorse is the only creature where the male has a true reversed pregnancy. The fertilisation and the gestation takes place in the males rather than in the females.
The female transfers her eggs to his pouch which he self-fertilises in the pouch. The number of eggs can vary from 50-150 for smaller species to 1500 for larger species.
His pouch is a complex organ that regulates temperature, blood flow and water salinity for the eggs as they hatch so the babies. They receive everything they need in the pouch from oxygen to food. Gestation time varies from 14 days to 4 weeks.
The male seahorses have evolved in this way to perpetuate their species at a faster rate. The female uses her energy for making more eggs rather than carrying fertilised ones. The males provide a safe and controlled environment for the babies.