Mollies

Molly

The Molly is actually more than one species. This fact sheet is an attempt to give information common to the two species most frequently kept in aquariums. One of the most popular species of Molly is the Sailfin Molly, Poecilia latipinna. The other common Molly is Poecilia sphenops. 

The Mollies are in the same genus as Guppies, Poecilia reticulata. Mollies tend to be bigger than Guppies, and Sailfin Mollies normally grow to about 4 inches (10cm). Under very good conditions will grow much bigger than this. Mollies in the Brisbane River are reported to reach 7 inches (18cm).

Origins

The Sailfin Molly comes from North America from the Cape Fear drainage in North Carolina, USA to Veracruz, Mexico. It has also been caught in the open sea of the Gulf of Mexico.

"Poecilia sphenops comes from Central and South America, from Mexico to Colombia.

Water Conditions
The Molly is a salt loving tropical fish. They don’t do well in water that is too pure in the sense that it is lacking in salt. They will even live in pure sea water, and are sometimes added to marine aquariums. A suitable temperature is 24̊ C (75̊ F). They prefer alkaline water, and like plenty of hardness.

Food
The Molly is an omnivore with a preference for vegetable matter. They relish live food like daphnia and mosquito larvae like most fish, but also eat soft algae. A normal fish food is suitable, and some people like to supplement this with algae wafers or spirulina flakes.

Companions
The Molly can be kept as a community fish as long as you choose suitable companions. Mollies are a little bigger than many of the small fish often kept together. Mollies are generally peaceful fish, but I avoid putting them with Siamese Fighting Fish. I know of one case where two male Mollies were kept with a male Siamese Fighting Fish and repeatedly attempted to mate with it. Eventually the Mollies harried the poor fighting fish to death.
Some suitable companions for Mollies are Glass Bloodfin Tetras, Emperor Tetras, Black Widow Tetras, Peppered Catfish, Swordtails and Platies. The Guppy and the Endlers Guppy are special cases as explained under Breeding.

Breeding
Mollies are live bearers and are easy to breed. They are not quite as easy as the Guppies. The breeding of many fish is affected by day length. Guppies are encouraged to breed by a long day length. Mollies, even more so. To breed Mollies, I suggest having at least 13 hours a day of light. The light can be either natural or artificial, or a combination of the two.
Mollies are from the same genus as Guppies and Endlers Guppies. Mollies will hybridize with Guppies. (I don’t have any information about Molly-Endlers Guppy hybrids, but this also sounds possible.) The Molly-Guppy hybrid is a drab looking fish. I’ve never crossed them myself, but I’ve seen the hybrids. These hybrids are reportedly sometimes fertile. I’ve never seen the second generation from this cross.
I’ve also heard reports of Mollies crossing with Platies and Swordtails, but I have considerable reservations about these reports.

Pest Fish
Any fish released or that gets away and gets into natural waterways is a potential hazard to the native fish of the habitat. In some parts of Queensland Mollies are becoming a problem. In Queensland, Mollies can legally be kept in aquariums, but not in situations where they can get into natural water ways.

Sources and Picture Credits
I gratefully acknowledge information from a Fish Note of the Queensland Government, Aquarium Life, Aquatic Community, and Fish Lore.

Steve Challis