Mollies 101 (Interesting Facts, Diet, Care, Breeding, Etc.)

Mollies 101 (Interesting Facts, Diet, Care, Breeding, Etc.)

Molly in a tank

Mollies are a popular choice for novice aquarists as they can survive in various conditions.

These fish are peaceful and social. So, many aquarists house them with other fish species.

Let’s learn about mollies in more detail.

Molly Species Overview

The molly fish, part of the Poeciliidae family, inhabits the waters of Central America and parts of the southern United States.

Wild mollies have a dull, silvery-gray hue, while captive mollies come in various colors.

Mollies mainly inhabit freshwater habitats but can thrive in saltier environments such as brackish waters.

Mollies are also known to inhabit shallow marine habitats such as harbors and waters surrounding mangroves.


Beautiful molly

The body of a molly has a wide midsection and a triangular head, tapering to a point at the snout.

Its tail has a fan shape, tapering off at the bottom.

Male and female mollies can be identified by their size, with males usually being smaller.

Additionally, a male molly’s anal fin is pointy, whereas a female’s fin is broad and fanned.

Many female mollies also have a “gravid” spot which indicates pregnancy since it’s used to hold their young ones.

Names of Molly Species

Mollies belong to the genus “Poecilia” in the family Poeciliidae. Currently, there are 40 known types of mollies.

Mollies inhabit various environments across the Americas and Mexico.

The different species of mollies are listed below:

  • Amazon Molly,
  • Balloon Molly,
  • Balsas Molly,
  • Black Molly,
  • Broadspotted Molly,
  • Catemaco Molly,
  • Cauca Molly,
  • Dalmatian Molly,
  • Dwarf Molly,
  • Elegant Molly,
  • Hispaniola Molly,
  • Liberty Molly,
  • Lyretail Molly,
  • Mangrove Molly,
  • Mountain Molly,
  • Pacific Molly,
  • Peten Molly,
  • Sailfin Molly,
  • Shortfin Molly,
  • Sulphur Molly,
  • Yucatan Molly, etc.


Most mollies live longer in the wild than in captivity.

This is because since aquariums are closed environments, it’s easy to upset the water balance in them.

You also can’t compare aquarium conditions with those of the natural habitats of the fish.

The typical lifespan of a molly in captivity is between three and five years.

However, the average life span can vary depending on the specific molly species.

So the best you can do is to provide them with a conducive aquarium environment and a well-balanced diet to extend their lifespan.

Average Size

In the wild, mollies are known to grow up to 5 inches in length, slightly bigger than the mollies living in captivity.

When kept in a captive environment, an adult molly grows up to 4.5 inches in size.

Female mollies are usually bigger than males. Male mollies grow only around 3.5 inches in length.

Due to their small size, these fish don’t need large aquariums and can be easily kept in a smaller setup.

Sailfin molly can grow up to five or six inches in length, making them quite large among all the molly species.

Mollies Tank Setup

Molly tank

Mollies are incredibly comfortable living in an environment that replicates their natural habitat.

So it’s important to maintain appropriate water conditions and provide a suitable tank ecosystem to keep the mollies healthy.

Let’s understand the tank requirements of mollies in more detail.

Tank Size

Due to their tiny size, mollies don’t need large tanks to thrive. They can flourish in small aquariums of 10 gallons or more.

The aquarium size can be determined by the number of mollies you plan to keep.

A small-sized aquarium of 10 gallons is adequate for up to four mollies.

An additional three gallons of water per fish is required for all the inhabitants to live comfortably.

Tank Equipment and Decorations

Create a natural environment for mollies in your fish tank with vegetation and shallow waters.

When setting up your tank for mollies, put sand or gravel substrate at the bottom.

You can use the substrate to anchor aquatic plants like Java Fern and Anubias.

These plants will provide the required shelter to mollies.

Add caves, rocks, and decorations to the tank to provide more shelter to your mollies.

Moreover, algae will grow on these surfaces and be an excellent food source for your fish.

For optimal well-being, these fish should be kept in well-lit tanks to support aquatic plants.

However, the lighting shouldn’t be overly bright.

Given below are the items needed in a molly fish tank:

Maintenance is vital to keep the pH levels of the tank water within the desired range.

This will ensure that your fish are comfortable and happy.

Molly Fish Care

Healthy molly

Mollies are extremely popular with aquarists because of their easy-going nature. They can also thrive in a variety of conditions.

However, like any fish species, it’s essential to take proper care of them and provide a well-balanced diet.


In the wild, mollies feed on invertebrates and plant matter like algae.

So provide your captive mollies with similar food to mimic their natural diet.

Mollies mainly feed on plant matter.

They aren’t considered top algae-eaters, but they enjoy a light snack of algae every now and then.

They use their lips to scrape off the delicious algae from rocks, wood, or glass surfaces.

In addition to algae, these fish like to munch on boiled veggies such as lettuce, spinach, and zucchini.

As omnivores, you can feed them fish flakes and live and frozen food to meet their protein requirements.

It’s essential to provide mollies with a nutritious diet to keep them happy and healthy in captivity.

Some of the live food that you must feed your mollies are:

  • Brineshrimp,
  • Bloodworms,
  • Daphnia,
  • Insect larvae,
  • Small-sized insects, and
  • Glass worms.

Mollies shouldn’t be fed for more than a couple of minutes at a time to prevent overloading their digestive system.

Feed them a pinch of food twice daily. It will ensure that they remain healthy and active inside your aquarium.

Water Parameters

Mollies are found in various natural habitats, from freshwater rivers to brackish waters and even the open oceans for short spans.

This wide distribution of mollies is quite remarkable.

The ideal water parameters for mollies are:

Water Temperature: 72°F to 78°F. (22.2°C to 25.5°C)

Water pH: 7.5 to 8.5

Water Hardness (dGH): 15 to 30 dGH

Tank Maintenance

Regular water change is a great way to keep an aquarium in good condition.

Water in freshwater aquariums should be changed by 10% each week for initial setups and 25% once a month for long-standing tanks.

Regularly cleaning your aquarium’s filter, substrate, and decorations will also help to maintain them in good condition.

Using an algae scrubber, water conditioner, and gravel vacuum can simplify tank upkeep and guarantee proper hygiene.

Finally, to keep the aquarium’s water well-conditioned, use a liquid test kit to monitor its parameters.

Common Diseases

Mollies, like other fish, can contract various diseases.

Given below are some of the common diseases that can affect mollies:

  • Fin rot,
  • Flukes,
  • Ich,
  • Bacterial infections,
  • Parasitic infections,
  • Shimmies (Molly disease),
  • Tail rot, and
  • Velvet.

To keep your fish healthy, change the water regularly and scrub its bottom thoroughly to prevent infections.

Mollies Behavior and Temperament

Mollies are shoaling fish. So it’s best to keep at least four of them together.

A group of more than four mollies is ideal. These fish are peaceful and do well with other fish species too.

Mollies often swim together to explore the tank, then separate to do their activities.

However, keeping them in cramped conditions or with aggressive tankmates can lead to aggressive behavior.

Mollies are an ideal choice for community aquariums because of their peaceful behavior.

Molly Tankmates

Molly with tankmates

Mollies are peaceful and social in behavior. As a result, they are often part of community aquariums.

However, mollies can exhibit aggression when kept in overcrowded tanks or with other aggressive fish.

To ensure mollies feel comfortable, they should be housed with other non-aggressive fish and in an adequately large tank.

Moreover, buying at least four of these fish is recommended before introducing other types of fish into your aquarium.

Some of the compatible tankmates that you can keep with your mollies are:

Avoid keeping mollies with goldfish because their water temperature requirements are different.

Besides, mollies can nip at goldfish fins.

On the other hand, bettas are territorial and aggressive. They will attack any mollies that intrude on their territories.

Mollies can also nip back at bettas fins. So it’s best not to keep them together.

However, there are ways to keep mollies and bettas together.

Given below are some fish species that you should avoid housing with mollies:

Keep mollies with compatible tankmates to maintain peace and harmony inside the aquarium.

Breeding Mollies

Mollies are livebearers, meaning they give birth to live young fry instead of laying eggs.

To breed mollies, select male and female mollies that are compatible.

Female mollies usually breed with the most prominent male in the aquarium.

Breeding mollies in a controlled environment is the best way to ensure a high survival rate for their fry.

Set up a separate tank for breeding with a warmer water temperature, up to 78°F.

To mate, the male molly will start a courtship dance.

The male molly will fertilize the consenting female by inserting his milt into her body through his anal fin, called a gonopodium.

Female mollies can produce up to 100 offspring and usually take up to 35 to 45 days to give birth.

Before giving birth, she will move to a dimly lit corner of the aquarium.

Once you notice this, immediately move the female fish into a breeding box.

Mollies show no parental care and try to eat their offspring.

So the breeding box can hold the female while the fry pass through a separate opening at the bottom.

An adult female molly can have up to 100 babies at a time.

The newly born fry should be fed with infusoria or powdered fish food.

Once the fry grow, transition them to baby brine shrimp until they can eat regular food.

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