Everything You Need to Know to Care for Molly Fish


Everything You Need to Know to Care for Molly Fish

Have you ever wanted to learn how to care for Molly Fish? Read on and you’ll learn everything you need to know about keeping your Mollies happy and healthy!

Mollies are freshwater fish indigenous to the Southern USA, Mexico, and Central America. They are similar to guppies, as they are of the same genus but different species.

They belong to the Poeciliidae family, with hardy properties that make them easy to care for. Those hardy characteristics make them a good choice as a beginner fish for amateur aquarists.

Mollies are quite popular as freshwater fish but can also live in brackish water and occasionally saltwater (it is even possible to convert them)!

Quick Facts

Characteristic Detail
Temperament Peaceful
Care Level Easy
Color Varied
Diet Omnivorous
Adult Size 4.5 inches
Lifespan 5 years
Water Temperature 72°F to 80°F
Water pH 7.5 to 8.5
Tank Size 10 gallons

Molly Fish Overview

Molly fish, Poecilia Sphenops, are one of the most popular freshwater fish species in the aquarium trade. They are hardy fish that inhabit slow-moving waters in the wild.

Mollies are easy to care for, making them a good choice as a beginner fish. They come in various colors and shapes that suit every aquarist’s goals. They are active and will make for a good social group in your tank.

Typical Behavior

Molly fish are active fish that love to stay in slow-moving waters. They are peaceful fish that will only show their aggressive traits when surrounded by more assertive tankmates. They will likely not show any sign of aggression if the tank is large enough to accommodate them.

Mollies are social fish that love to shoal. Keeping them in groups consisting of mostly females is good as too many males can cause harassment for the females. Mollies are fun to watch as they grace your tank with their beauty and playful demeanor.


There are various types of Molly fish, each with a distinguished appearance and personality. Most types of Molly are similar to the common Molly fish, Poecilia sphenops. The major differences between these types of fish are their patterns and colors.

They can also differ in shapes and sizes, like the Balloon Molly, depending on the species you are comparing. The common Molly has a flat body trunk that allows it to surf the waters. It has a unique body shape that is tall in the middle and narrows towards the end.

The common Molly has a large fan caudal fin that can come in transparent or colorful form. It also has dorsal fins that can flatten against its body or spread out in the form of a fan, like its caudal fin. Female mollies are usually larger than males.

The females can reach a 4.5-inch size while males grow to about 3 inches. Pregnant females even tend to have larger bodies as they have a swollen stomach that makes them appear larger. Female Mollies have an anal fin with a fan shape, while males have a pointier shape.


Life Span

Mollies have a habit of living longer when provided with adequate care. If you take good care of your Molly fish, you will likely be surprised at how long it lives.

In captivity, mollies can live up to 5 years under adequate conditions. In the wild, they tend to live between 3 to 5 years, making the importance of proper care clear. Although Mollies are a hardy fish, it is still important to meet their basic requirements.


The way size works in Mollies is quite similar to their lifespan. The size your Molly attains depends on how well you feed it and the conditions you provide. In other words, both their feeding and living condition will affect their overall size.

Depending on the species, your molly can reach over a whopping 5 inches in size under adequate conditions. They tend to reach a larger size in the wild as they have more space to explore. They can reach 7 inches and more in the wild, which might be impossible in captivity.


Sexing is quite easier in Mollies compared to some other fish that can be more challenging. It is easy to see the difference between male and female Mollies as the females tend to be larger. The males also have a sailfin that is absent in females.

You can even tell the difference even more clearly when the females are pregnant. They become more puffed up and develop a dark spot at the base of their anal fin.

Tank Mates for Molly Fish

Mollies are peaceful and hardy fish, which allows them to have a wide range of compatible tank mates. They will make good tankmates with almost all kinds of fish species you decide to stock.

You won’t have much trouble if you intend to provide your Molly fish with a companion. You only have to consider some factors before making your choice of tankmate.

Avoid having aggressive fish in the same tank as your Mollies. It would be best to keep similarly-sized fish to avoid the fish from bullying or even eating your Mollies.

Compatible tank mates for molly fish include:

Best Water Conditions to Care for Molly Fish

Water is one of the major determinants of your Molly’s wellbeing. You have to make sure you provide them with adequate water conditions and requirements for you to get the best out of them.

Temperature for Mollies

Mollies love to stay in cool waters. They will thrive in waters within the temperature range of 72 to 80 degrees Fahrenheit. You should make sure you do not exceed this temperature range for the wellbeing of your Molly.

It is recommended to use an aquarium heater to keep the recommended setting’s water temperature.


pH Level

pH level refers to the level of alkalinity or acidity of the water. You have to provide an adequate pH level for your Molly fish. Molly fish prefer slightly alkaline waters, so the pH level should range from 7.5 to 8.5.

Oxygen Level

As with most fish, these fish need to live in well-oxygenated water; for this, I recommend installing an air pump into your aquarium to ensure that the water is well oxygenated.

Best Tank Setup to Care for Molly Fish

When selecting a tank to care for your mollies, we need to consider the fish’s needs. Some essential needs of the fish include:

  • Mollies are graceful swimmers and prefer to have a large tank to swim around.
  • They love to stay in slow-moving waters, so you should have areas where they can avoid the powerful current.
  • Mollies love to have sandy substrates as it resembles their natural habitat.
  • They love to nip at plant leaves, so it’s a good idea to add live plants to the tank.
  • Mollies love to have decorations in their tank to help them find shelter.

Tank Size for Molly Fish

Mollies are fast-growing fish. They will reach their adult size within a year or two. You will need to provide the appropriate tank size for them. Providing them a large-sized aquarium will allow them to swim gracefully.

Mollies will do well in a 10-gallon aquarium. They love to shoal, so you can have 2 to 3 mollies in your 10-gallon aquarium. Remember to follow the rule of thumb that you want ~ 1-2 inches of fish per gallon of water.


The cleaner your tank water is, the more chance your fish have of thriving and living a happier and healthier life. I have always used a Fluval aquarium filter which I highly recommend – in a future article we discuss other filter types.

Tank Decorations

Mollies love to have decorations and structures in their tank. You can enhance the appearance of your tank by adding decorations to it. Here are some suitable tank decorations for your molly fish:

  • Ludwiga
  • Driftwood
  • Pondweed
  • Duckweed

Best Diet to Care for Molly Fish

How often do mollies need to be fed?

Mollies are not heavy eaters. You will only need to offer them a small amount of food. You can feed them two times a day. When feeding your mollies, you have to understand a key factor, which is moderation.

What should I feed my Mollies?

Mollies are omnivores and will feed on a wide variety of food. Their diet ranges from carnivorous food groups to plants. You can feed your Mollies with fish flakes, pellets, and vegetables.

You can also treat your Mollies to a meal of live food or freeze-dried foods for a more healthy diet. Mollies will also eat wafers, plant materials, some invertebrates, and algae.

How long can molly fish live without food?

You might be wondering if your molly can live for days without food. It would surprise you to know they can live longer than days, under adequate water and tank conditions, molly fish will live up to two weeks without food.

Breeding Molly Fish

The breeding process of molly fish is an interesting thing to experience. They are a frequent breeder and will breed several times in their lifetime. Most times, their breeding does not require human help or intervention.

One interesting fact about Molly fish is they are livebearers. They birth their young ones alive. Female mollies love to breed with larger males.

As the breeding season approaches, you will see the male and the female Mollies courting each other. After court, the female allows the male to fertilize her eggs. The eggs develop and hatch in her before releasing them to the outer world.

After fertilization, the female’s stomach starts to protrude as it accommodates her eggs. It will take up to 30 to 45 days for the babies to develop in her. It might be best to separate the expectant mother and put her in a separate tank.

If you want a higher survival chance of the fry, you will need to breed the molly fish in a controlled environment. The temperature of the water should be 78F. You will also have to remove the mother as soon as she births them.

Consider getting a breeding box:

How to tell if my Molly fish is pregnant?

The most visible sign that your Molly is pregnant is her protruded stomach. You will also notice a triangular dark spot near her anal vent. As Molly’s pregnancy progresses, the signs become more obvious.

Molly Fish Diseases

Here are some common diseases that can affect Mollies:


Constipation is one of the common diseases that affect Molly fish. It mainly occurs when you feed your Molly with excess food. It will result in difficulty indigestion. Your Molly will also not be able to pass out stool. You have to make sure you do not overfeed your Molly to avoid constipation.

Swim Bladder Disease

The swim bladder disease is also another common disease that affects Mollies. It can be a result of bacterial infections or as a result of digestive issues. This disease causes the swim bladder to malfunction and prevents the fish from swimming properly. If you do not give special attention to the fish, it can cause the fish to drown and eventually die.


Vibriosis is also a bacteria-caused disease that affects Mollies. It occurs when the Vibrio bacteria infect the fish, causing a deterrent to its health. You have to take certain actions to ensure your molly fish is in good health. You also have to maintain adequate water conditions to prevent the disease.

Frequently Asked Questions

How many Molly fish can I keep together?

Mollies are active and social fish, so you need to keep them in groups. You can keep them in groups of 4 or more. You also have to make sure you keep them in a large enough tank that will accommodate them though.

What does a pregnant Molly fish look?

The major difference between a pregnant and normal molly is the protruded stomach. A pregnant Molly fish looks inflated. You will notice her protruded belly and a dark spot near her anal vent.

How Should I Care for Molly Fish?

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