Because male sea horses are the ones who get pregnant, they can be differentiated from female sea horses by the presence of a brood pouch on their abdomen.
Sea Horse Background
More than 40 species of sea horse (Hippocampus) exist. Sea horses are classified as fish. Even though they do not look like fish, they have gills and fins like fish though they lack a dorsal fin. Their unique tails allow them to grab onto grasses in the water so they can stay in one place to feed. Because sea horses lack stomachs, food passes through their intestines quickly requiring daily feeding to prevent starvation.
Determining the Sex of a Sea Horse
The only visible difference between male and female sea horses is the brood pouch. This pouch holds the fertilized eggs meaning only the males have these pouches. The pouch is located above the anal fin and below the male’s abdomen. The presence of the pouch means the male's abdomen smoothly connects to the tail giving the male sea horse's abdomen a curved appearance. The female abdomen connects to the tail at more of an angle giving her body a blocky appearance. These distinctions can be difficult to notice in small or young sea horses. As they grow larger or as the male's brood pouch becomes more pronounced during pregnancy, the differences are easier to spot. In some sea horses, the pouch is slightly darker than the rest of its body.
Sea Horse Mating
Sea horses form monogamous, long-lasting bonds with their mates. Female sea horses go into male territories looking for a partner. When she finds one, she bonds with him and reinforces their connection each morning by visiting him. During the visit, the two sea horses will change color and swim around one another for several minutes. This ritual occurs prior to mating and throughout the male's pregnancy.
When the sea horses are ready to mate, the female injects her eggs into the male's pouch using an ovipositor. The eggs are then fertilized by the male inside the pouch. Everything about the pouch resembles the womb typically found in females of most species, including fluid that feeds and protects the growing embryos.
Sea Horse Reproduction
The male will carry the fertilized eggs for two to four weeks. The gestation period depends on the species and the water temperature with birth coming faster in warmer water. The male will begin rocking back and forth while making a squeezing movement in his body to push out the babies that appear as small versions of the adults. Males can give birth to 5 to 1,500 babies at one time, although the average is between 100 and 200.
As soon as the male delivers the babies, his partner will return to court him again. He can become pregnant again right away.