Hot Water Fish

Molly Fish, Poecilia

  • Scientific name: Poecilia
  • Common Name: Molly
  • Aquarium size: 80 liters
  • Temperament: Calm
  • Temperature:  Between 24º and 26º
  • pH: Between 7 and 8.5
  • Diet: Omnivore
  • Length: 8 cm for males. 12 cms, females


The Molly is a fish of the Poecilidae family , which in turn are included in the Cyprinodontiformes group. Surely you have already realized that they are a close family of the Guppy fish , with which they share gender and family.
There are many varieties of Molly fish, some from nature and others from numerous crosses between different species.


Adult Molly can measure between 5 and 12 centimeters, depending on whether they are male or female.
They have a slim body, with a slightly pointed head and mouth, where we find very sharp teeth. Their fins have soft rays.
The coloring of the Molly fish is very diverse, the result of the different crosses made by aquarists. In its natural state this fish is black and speckled in yellow, however for sale we find Molly of black, orange, marbled, white, red, gold, Dalmatian, albino … the quantity is large and from time to time, we are surprised with a new hybrid of fish Molly.
To distinguish them from the Guppies ,Molly’s have a thicker body and their fins are not elongated , rather rounded.

Differentiate male and female Mollys, sexual dimorphism

In Molly fish, sex can be differentiated from 2 to 3 months of age . This is great information, if we want to establish a breeding program for Mollys, or maintain a good balance in the aquarium.
These are the main morphological differences between male and female Mollys:

  • Anal fin. The anal fin is the one near the tail, in the ventral area (below).
    Molly males have elongated, tube-shaped fins. This is your reproductive organ, the gonopod .
    In females, the anal fin is fan-shaped.
  • Size. Males are usually between 5 and 8 centimeters long, while females can be centimeters long.
  • Body shape. The females have a more rounded body than the males, more stylized, thin and elongated.
  • Coloration. Molly males have more striking and brilliant colors than females.

Molly types

When we speak of Molly fish we are generalizing, and including the name «Molly fish» to a good variety of Poeclilias. Some of the best known and that we can find in aquariums around the world are:

Molly Ball Fish

The Molly ball has the same characteristics as the rest of the Mollys, but is more rounded and with a prominent belly. The colorations of these fish are similar to the rest of the Mollys.

Molly swordfish or Molly swordtail

This is a fish from which there are many varieties to choose from, also all equally striking for their colors and veils. It is not usual, but sometimes this fish changes sex, transforming a female into a male.

Dalmatian Molly Fish

This is a very striking Molly, full of black polka dots on a silver background, which has earned her the nickname «Dalmatian» for the breed of dog. It is a variety of poecilia that comes from Mexico, calm and active at the same time. Ideally, you should have one male for every 4 females.


Dalmatian Molly Fish

Black molly

The Black Molly or short-finned Molly is one of the most original for its coloration, completely black in the male. It is a very calm fish that can coexist with other poecilia, even with the risk of hybridizing, since they reproduce easily.

Distribution and habitat

In the wild it can be found in many parts of the world, although they are native to the southeastern United States, Venezuela and Colombia to Mexico. Isolated populations are known on some islands in the Caribbean.
They are fish that usually live in the mouths of rivers, so they endure a certain degree of salinity in the water.
It is not usual that we buy a free-range Molly, the ones that we will find in pet stores, are fish raised in China or in Eastern Europe , just to be commercialized.

Aquarium conditions

The aquarium must have a minimum of 80 liters , if it is larger the Molly fish will be perfect. They are fish that need a lot of space to swim, and they also need an abundance of vegetation and surface plants.
The temperature of the aquarium must be in the environment of 24º to 26º , and although they are not too demanding with the composition of the water, they are in an ideal environment with water with a pH between 7 and 8.5 and a hardness 15- 30 dH.

Ideas for setting up your aquarium

  • Best complete aquariums
  • Best Small Aquarium
  • Best external filters for aquarium
  • Best aquarium heater
  • Best Aquarium Oxygenator
  • Best Aquarium LED Display
  • Better sand
  • Best substrate for aquarium
  • Best compost for plants
  • Best Aquarium Stones
  • Best aquarium logs
  • Best Aquarius Test
  • Best Ph meter 
  • Best fish food
  • Best Fish Food Dispenser


Molly is omnivorous. In the wild, it feeds on worms, crustaceans, insects, algae and plants.
In the aquarium they will gladly take prepared dry food, but from time to time, it needs a good supply of algae or spinach, to which we must add brine shrimp, mosquito larvae …
It is recommended to feed them two or three times a day, but in small quantities.

Behavior and compatibility

It is a fairly peaceful fish, although adult males can become somewhat territorial.
In stores it is easy for them to sell us a pair of Molly fish, a male and a female. The ideal is to keep between three and five females per male , since it can harass her. In nature, each male is surrounded by several females.
Good tank companions could be some rainbow fish and tetras , which are tolerant of hard water.

Molly fish compatibility

Unrestricted Molly Compatible Fish

  • Tiger Barbel
  • Scalars, Angelfish
  • Guppy
  • Neon Tetra
  • Silver dollar
  • Rasbora Galaxy
  • Kribensis
  • Betta fish 
  • Platy
  • Ancistrus

Unrestricted Molly Compatible Fish

  • Boraras
  • Cherry barbel
  • Harlequin
  • Botia Clown
  • Drunk
  • Corydora
  • Little nun
  • Ax fish
  • Telescope
  • Disk

Unrestricted Molly Compatible Fish

  • Gourami Pearl
  • Chinese neon
  • Snail Apple
  • Zebra fish
  • Ramirezi

Restricted Compatible Fish

  • Koi carp
  • Rainbow
  • Killis
  • Paradise
  • Wasp Fish

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