The round shape of its tail must be the reason for its name though that having said, every female nearly always has a round tail no? Amazing how much variety you can create with guppies. It took me half a year before i could go create colours myself years ago. Roundtail guppies have a short tail with curved, rounded edges that extend to about half the length of their body. The shape is similar to tails seen in wild stock, but recent interest from European breeders have increased the popularity of this morph.