Seahorses are monogamous. The males incubate the eggs that are received from the female. Females do not play any parental care after mating. Fertilization and incubation of oocytes received from female takes place in a sac-like brood pouch located under the tail. Male brood pouches in seahorses are the most advanced among all syngnathid species, opening only through an anteromesial pore. The seahorse is sex role reversed. The males exhibit higher levels of behavior patterns and males have the two most overtly aggressive behaviors in courtship, such as tail wrestling and snapping with the snout. Sex role is not synonymous of parental care.
The main idea is that male seahorses have a brood pouch which protect, osmoregulate and aerate the eggs in compartments located in the placenta. After an appropriate period of courtship (sometimes lasting up to 9hrs) female seahorses deposit their eggs directly inside the male pouch using a tube-like ovipositor. This direct insertion into the male pouch ensures that no stray sperm can get to the eggs before the male in question can mix them with his own sperm. The fertilized eggs get embedded in the pouch wall and are bathed in a fluid that proves nutrients and oxygen, as well as carefully regulating salinity levels to make sure the embryos develop normally.
The reproductive period of the lined seahorse, in Chesapeake Bay appeared to start in May and finish in October. Newborn seahorses are released by ejection from the brood pouch by body contortions and a pumping action of the pouch. The period of pregnancy may represent a high energetic cost for the male seahorse, which may reach extremes during the time they are giving birth. Fertility may vary depending on different habitats. Lockwood reported up to 1000 juveniles inside the brood pouch whereas Bohlke usually found 250-400 eggs. Gestation usually last only about two to three weeks. Then the males go into “labor”. The young emerge as little replicates of their parents and can feed and defend for themselves. In the wild there is a high mortality rate though, usually sometimes more than 90%.