How do male seahorses brood eggs?

While the order Gasterosteiformes includes a diverse range of fish, such as sticklebacks and trumpetfishes, it is specifically the seahorse—a member of the family Syngnathidae—that exhibits a unique form of male pregnancy.12

After an elaborate courtship dance, the female uses her ovipositor to deposit eggs into a specialized brood pouch located on the male’s abdomen or at the base of his tail. The male then releases sperm into the pouch, where fertilization occurs.342

The developing embryos remain in the pouch for 10 days to six weeks, depending on the species. During this period, the male provides essential care by regulating the internal fluid chemistry, gradually transitioning it from his own body fluids to salt water. The pouch lining also supplies the eggs with oxygen and nutrients. Once development is complete, the male undergoes muscular contractions to expel the fully formed, miniature offspring into the water.43