This varies greatly between species. It can be as short as 60 days after birth, or as long as 12 months. Body size is the determinant for sexual maturity. In general, males reach sexual maturity shortly before females.
Seahorses are monogamous for the gestation period. The length of the breeding season and the time of the year in which it occurs varies between species and is affected by nutrient availability and temperature. Once males are sexually mature, they begin looking for a mate.
The males become aggressive toward other males and their behavior includes: pushing snouts and tail hooking to show strength. Once a female is wooed, she deposits her eggs into the male’s brood pouch with her accessory organ.
The brood pouch on male seahorses is located in its tail. Soon after, the male releases his sperm into the pouch. Seahorses have very few sperm in each testicle (as few as 150 per testicle in some species).
The embryos begin to develop, and the male’s tissue inside the brood pouch changes. The brood pouch is lined with a muscular wall and layer of stroma and epithelium. This creates an “incubation cavity” for developing zygotes. All of the roles of the pouch are not understood, but determined roles include: protection, thermal regulation, nutrient transfer, immunoprotection.
The gestation period of seahorses varies between species, but can be as short as three weeks. During this time, the males do not move (as little as a few centimeters a day in some species). The females attain food for the impregnated male.
The fry are then hatched out of the pouch and left to fend for themselves. Soon after (has been documented as a few hours) the male begins searching for a mate.
Seahorses do not mate for life, a new suitor can produce the next batch of fry.