Guppies come in a large assortment of colors and variations. They can be different sizes, and can have colors ranging from drab gray to white, yellow, brown, red, blue, gold, and iridescent. Even the females can be quite colorful and beautiful, though not usually so showy. So how do you tell the difference between female and male fancy guppies?
It is far easier than most people might think. It should be stated at the outset, though, that judging the sex based solely on the color isn't always successful. As previously stated, female guppies can be tremendously and surprisingly colorful. In many animal and fish species, the female is the drabber of the two sexes, however judging based only on color may not say much when trying to determine the gender.
There are some male guppy specimens, which may be rather dull, with just a small amount of color. There may also be females that are much more colorful than those male individuals. Still, there are some things that set the two apart.
For one thing, except for when the guppies are immature, female guppies are nearly always larger than the males. A large adult male may be close to the same size as a small adult female, however even then the female tends to be much more full bodied, both top to bottom and side to side.
This is necessary since the offspring will develop inside the female who will then give live birth to her young. The male doesn't have this restriction, so he can grow both smaller and less full bodied without causing a problem with reproduction of the species.
The fins of the female also differ from those of the male. As with many fish species, males need to be 'showier' to attract the females. This can include being more colorful, but as previously mentioned, the females can at times also be colorful (most tend not to be, there are simply exceptions to this rule).
However the caudal fin or tail fin in a male is nearly always quite large for his body size, and most often has almost a shimmering quality to it as the male swims through the water. In contrast, the female has no need to attract a mate, and her fins, especially the tail fin, are generally small and functional rather than being primarily designed to attract a mate. They are also more rounded than the caudal fins of the males, which can be nearly straight from top to bottom and extend much above and below the base of the tail. Some males may even have tails that are longer on top than on the bottom, again unlike the more rounded fin of the females.
The size and shape of the caudal fin is one of the easiest to recognize differences between male and female guppies, and one that can be seen even at a distance.
If you are new to having guppies, it will probably not take you very long to be able to tell the difference between the males and the females with little more than a glance. In fact, since there are so many visual differences, guppies are one of the easiest aquarium fish to be able to identify by gender.