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The Common Molly, the Sailfin Molly and hybrids


The Molly is a very popular, livebearing fish amongst both novice and experienced aquarists.

The Molly is resilient, easy to keep, is easy to breed and comes in a wide range of colours and a wide range of fin types. Being a livebearer, it is an ideal fish for novice aquarists to breed successfully.

Origins of the Molly

The Molly is a freshwater tropical fish which can also tolerate brackish water and seawater and it is found in the wild in Mexico and Central America. There are numerous hybrids in the Molly family which result from the hybridization of the Common Molly (Poecilia sphenops) and the Sailfin Molly (Poecilia latipinna)(depicted in the featured image above) as well as selective breeding to enhance certain characteristics such as colour and finnage.

Characteristics of the Molly

The Molly can enjoy a lifespan of up to five years and it is a good community fish but it should be noted that the male of the species can display aggressive tendencies.

As is typical with livebearers, the male tends to be more ornate than the female and significantly smaller. The male Molly will typically grow to around 3.2″ whilst the female Molly will grow to around 4.8″ in size. Since the Molly is not a small, tropical fish it is recommended that it is kept in a tank of 36″ in length or greater.

Being livebearers, the male Molly has a modified anal fin called a “gonopodium” through which (by consent or otherwise) it will pass spermatozoa into the female’s genital pore.

In the wild, the Molly will congregate in large shoals indicating that this is how it will prefer to live in an aquarium. It should be noted that the Molly is quick and because it can tend to display aggressive tendencies, it is better not to include slow-moving species or fishes with elaborate finnage in the same tank, as they could easily be harassed by the Molly.

Feeding the Molly

As is evident from the positioning of the mouth, the Molly is a top-feeder. It is omnivorous so it will enjoy both flake food as well as live food (such as daphnia, brine shrimp and bloodworm). As with all fishes, the Molly should not be overfed so feeding once per day should be sufficient, providing sufficient food that will be consumed in two to three minutes.

The Molly will be happy to browse on algae and plants in the aquarium.

The Molly – Video

Breeding the Molly

A typical brood of Mollies can number up to around 120 and of these, around 70% are likely to be female. This is quite typical amongst livebearers and is also an indication that for each male Molly you should have at least two female Mollies, preferably three in my experience.

As with all livebearers, the male Molly is ever-eager to mate so having two or three females for each male gives the female some respite from the constant attentions of the male.

By choice, the female Molly tends to choose to mate with larger male Mollies but, as is the way with livebearers, the male Molly is ever-eager to mate and will dispense with the mating ritual if his advances are unwelcome and simply launch a surreptitious mating if he can catch the female unawares.

The female is also able to store the sperm packages from males for several months so, in the absence of males, the female can use that stored sperm to fertilize batches of eggs. The female can also bear the young of different males (polyandry).

The breeding cycle is around 30 to 40 days so you can anticipate the addition of 120 fry around ten times per year.

The Molly, unlike the Guppy, will tend to eat the fry so you may wish to include Java Moss in your aquarium to offer some protection from predation to the fry. Similarly, you may also wish to consider providing a bolt hole in the form of strategically arranged rocks or even a section of a round, terracotta plant pot under which the fry can safely conceal themselves from predation.

Interaction with other species

In the wild, Mollies will shoal in their hundreds and are generally good community fishes but it should be noted that, as stated above, it is best to avoid keeping slow-moving species and species with elaborate finnage in the same tank as Mollies because male Mollies, in particular, can tend to be somewhat aggressive towards these types of fishes.

Larger or aggressive fishes (such as some Cichlids) have been known to target Mollies. One such culprit cited is the Convict Cichlid.

Susceptibilities of the species

In my experience, Mollies have lived perfectly happily in soft, freshwater but others have reported that in freshwater their Mollies have developed “shimmies”. It is worth remembering that, in nature, the Molly is often found in brackish water and even seawater.

The Molly is now a very hybridized species and, in addition to being susceptible to “shimmies”, as reported by other aquarists, hybrids with more elaborate finnage can also be susceptible both to fungal infections and to fin rot.

Varieties of Molly

Through selective breeding and hybridization the original, wild Molly now comes in a wide variety of colours and fin types, which will doubtless grow over time with further selective breeding. Amongst the more common types of Molly are the following:

  • The common (or short-tailed) Molly. This is if you will, the original Molly found in the wild and is a silver-coloured fish. Curiously, despite being a quite beautiful fish in its own right it is seldom seen in aquariums, as aquarists seem to prefer the more elaborate Mollies.
Common Molly
Common Molly – male
  • The Sailfin Molly. This variant of the Molly has the elongated dorsal fin. It is worth noting that the different subspecies of Molly can be bred to produce fertile offspring and it may well be the case that the Common and Sailfin Mollies were the original subspecies from which the now large variety of Mollies were hybridized and selectively bred.
Sailfin Molly
  • The Black Molly. As its name suggests, the Black Molly is entirely black. It is worth noting that black fishes tend to be more prone to diseases than other fishes so if you keep black Mollies then additional vigilance may be prudent.
  • The White Molly.
  • The Green Molly.
  • The Gold Molly.
  • The Balloon Molly. This variant of the Molly has a quite distorted body and is, as its name suggests, quite balloon-shaped. I don’t find it to be particularly attractive and it is known to be significantly more prone to ill-health than other sub-species of the Molly.
  • The Lyretail Molly. The tail fin (caudal fin) of this Molly is quite distinctively extended at the top and bottom edges and, as the name suggests, the caudal fin resembles the lyre (a musical instrument which is part of the harp family).
Golden Black Lyretail Mollies
Golden Black Lyretail Mollies
  • The Dalmatian Molly. This variation is usually characterized by black and white or black and silver scales intermingled along its body.
  • The Mexican Molly. This variation is closer to a Black Molly and not to be confused with the Common Molly, which is silver in colour and originates in Mexico and Central America.
  • The Neon Orange Molly.
Neon Orange Molly

Mike Wheeler

I started keeping freshwater tropical fish in 1972 and it has been something of a passion ever since. In this website, my aim is to build up an everyman's guide to help the everyday aquarist get the best from this inspiring and entertaining hobby.

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