On adult seahorses, determining the sex of an individual
is as simple as determining the presence or absence of a brood
pouch. The pouch is located only on males, and can be found
in the lower front of the abdomen, right below the anal fin.
This pouch gives the front of the male's abdomen a gentle
sloping silhouette from the lower chest to the tail.
The abdomen of the female joins the tail at a sharper angle
than that of the male, as seen on these two H.erectus.
The female does not have a brood pouch, so her abdomen joins
the tail at a sharper angle. Because of its position at the
"corner" of this angle, the anal fin of the female
is often easier to see than that of the male.
The male's pouch tapers from the anal
fin to the tail.