Section: Fish Profile

The popular and easy to care for molly, platy, guppy, and swordtail all belong to a family collectively known as live-bearing tooth-carps, or Poeciliidae. These fish closely resemble killifish and minnows. They are all natives of the tropical and sub-tropical regions of the western hemisphere, from Central to South America, where they live in small streams. These are peaceful fish, which make them suitable for the community aquarium. None of them grow much bigger in the wild than 6 inches and in the aquarium they barely grow to 4 inches.

Breeding

What distinguishes these fish is their method of breeding. Rather than lay eggs that the male then fertilizes, these fish hold their eggs internally. The male fertilizes them with a specialized fin called a gonopodium, and the young hatch within the female and then swim free. Females can produce several hatches of young from a single fertilization.
The two genera that make up most of the aquarium species are Poecilia, which include the guppies and mollies; and Xiphophorus, which includes the platys and swordtails. While the wild species are colorful enough (Poecilia means many-colored), hobbyists and breeders have taken advantage of their easy breeding habits to create dozens of vibrantly colored varieties.

Swordtails and platys have been interbred so much that sometimes there is little to distinguish one species from another, except the elon ...

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