Females, on the other fin, have one continuous larger slit, the anus located at the end of it. The slit is also located closer to the tail stock of the dolphin. The other way to determine the sex of a dolphin, if you can't reach their belly, is to look at their mellon, or head. The males tend to have a fatter, rounder mellon, while the females are more sleek and streamlined. There are various ways a dolphin has of showing that she or he is interested in sex.
Males are probably the easiest to detect.
If you are in the water, they may rub it along any part of your body, or wrap it around your wrist or ankle. Their belly will also be pinkish in colour, which also denotes sexual excitement. Females can be a little harder. The most obvious way a female dolphin has of displaying her sexual interest is the pink-belly effect. Their genitals become very pink and swollen, making the genital region very prominent.