The male guppies are about 3 centimeters long and are naturally smaller than the male black mollies. Both fishes, along with other similar aquarium pets, are viviparous; which enabled them to occupy an important niche in fish evolution.
Both the guppies and the black mollies are closely related to the swordtails, platys and mosquito fish.
Three 10 gallon aquarium tanks filled with de-chlorinated tap water were stocked with guppies and black mollies from a local supplier.