Among aquarium fish, few fish are as easy to breed to the guppy. This makes it easier to selectively breed guppies than most fish. As such, dozens if not hundreds of true-breeding strains or varieties of guppy have been produced by dedicated breeders. Guppies with selective breeding are called "fancy guppies."
One common type of guppy is the feeder guppy. These guppies are sold as food for other fish. They often resemble the original, wild guppy. However, many feeder guppies are culls -- fish rejected for selective breeding. This gives some feeder guppies bright colors and patterns more like fancy guppies.
Guppy hobbyists have selectively bred a wide variety of fin shapes. Most fancy guppies in pet shops have either fantails or deltatails. Guppies breeds with these fin shapes have long, flowing fins. However, fancy guppies at fish shows often have other fin shapes. The swordtailed guppy has a tail fin with a sword-shaped extension on the tail fin. Lyretailed guppies take this a step further, where the top and bottom of the caudal fin jut out, resembling a lyre. Swordtail and lyretail guppies show up at fish shows more often than pet shops.
Solid Color Guppy
Breeders have fixed a number of solid-color strains, also called uni-color guppies, which come in colors including blue, green, red and yellow. Some breeds of solid-color guppies from Russia, called Moscow green and Moscow purple, are hardy, long-finned fish. They have made appearances in guppy circles, but are not yet widely available in pet shops.
Some breeds are defined by a pattern instead of a solid color. In tuxedo guppies, the rear half of the body is black, but the tail and front of the body can be various colors. Some tuxedo guppies have an iridescent gold sheen. Snakeskin guppies also have a distinctive pattern: golden squiggly lines over a darker base color. In still another pattern, the peacock, darker spots stand out against a lighter background. Breeders have selectively bred numerous different color patterns and variations on them.