Molly Fish: Underrated Gems Of The Aquarium World

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I have had the opportunity to care for and breed several species of fish over the years.

Among them, molly fish have always held a special place in my heart due to their vibrant colors, lively behavior, and ease of care.

In this comprehensive guide, I’ll be sharing my firsthand experience and insights on these special fish that I love so much.

Molly fish are known for their hardiness and ease of care, which makes them a popular choice among beginner and experienced fish keepers alike.

Whether you are a seasoned fish keeper or a beginner, these fish are a great addition to any aquarium.

I’ll cover everything you need to know about these fascinating creatures, from their appearance and lifespan to their care, breeding, and tank setup.

So, let’s dive in and learn more about these fascinating fish!

History and Origin

The molly fish, or Poecilia sphenops, is a species of freshwater fish that belongs to the Poeciliidae family.

It is native to Mexico, Central and South America, and was first discovered in the mid-19th century.

The origin of the name “Molly” is unclear, but it is believed to have been named after a person or a place.

Some sources suggest that the name comes from the German word “moll,” which means soft, referring to the fish’s delicate appearance.

They were introduced to Europe in the late 1800s and were popularized as aquarium fish in the early 1900s.

The first molly fish to be successfully bred in captivity was a black molly, which was bred in Germany in the 1920s.

Since then, these fish have become one of the most popular freshwater aquarium fish species in the world.

They are known for their vibrant colors and unique shapes, and their ease of care makes them a great choice for both novice and experienced fish keepers.



Average Size

The average size of a molly fish is around 3-4 inches, with females being slightly larger than males.

Males usually grow to around 3.5 inches, while females can reach up to 4.5 inches in length.

When it comes to their body shape, these fish have a flattened body with a triangular head, wide mid-section, and narrow tail.

They have a dorsal fin, which runs along the top of their body, and an anal fin, which is located on the underside of their body.


Molly fish come in a wide range of colors, including black, white, silver, orange, yellow, green, and red.

Additionally, some fish have patterns such as spots, stripes, or marbled colors.

The specific color and pattern of these fish can vary depending on its species, genetics, and breeding.

Molly Fish Care


The lifespan of mollies can vary depending on their environment and how well they are cared for.

On average, they can live for around 3-5 years in captivity.

However, with proper care and attention, they can live for up to 10 years.

It’s important to note that female molly fish tend to have a shorter lifespan than males.

This is because they go through the stress of pregnancy and giving birth, which can take a toll on their overall health.

Molly Fish Types

Molly fish come in a wide variety of types, each with its own unique characteristics. In this section, I will discuss some of the most popular types of mollies.

  1. Black Molly – This type of molly fish is one of the most popular. They are entirely black and can grow up to 4 inches in length.
  2. Sailfin Molly – These fish has a large, sail-like dorsal fin that extends the entire length of its body.
  3. Balloon Molly – This fish has a unique appearance due to their rounded, balloon-like body shape.
  4. Lyretail Molly – A distinctive tail fin that resembles a lyre.
  5. Dalmatian Molly – A unique spotted pattern on their body that resembles a dalmatian.
  6. Gold Dust Molly – These fish have a shimmery gold color, hence the name “gold dust.”
  7. Mexican Sailfin Molly – This molly fish is similar to the Sailfin Molly, but it has a more elongated dorsal fin that can reach up to 4 inches in length.
  8. Marble Molly – A marbled pattern on their body, which can range from black and white to orange and silver.
  9. Short-Finned Molly – These mollies have a shorter fin than other types.
  10. White Molly – A white body color and are sometimes referred to as “silver mollies.”
Molly Fish Diet

Behavior & Temperament

I have found that molly fish are generally peaceful and social creatures that get along well with other fish.

They are normally not aggressive and rarely show any signs of territorial behavior.

However, it is important to note that like any fish, they can become aggressive if they feel threatened or if their territory is invaded.

I have read on some of the Facebook Groups that I am a member of, that sometimes a molly can be very aggressive and bully other fish.

I have not experienced this but it is worth noting.

Mollies are very active swimmers and enjoy exploring their environment.

They are known to be curious and will often investigate new objects in their tank.

They are also known to be jumpers, so it is important to have a secure lid on their tank to prevent them from jumping out.

One thing to keep in mind is that these fish are live bearers, which means they give birth to live young instead of laying eggs.

This can lead to overpopulation in a tank if not properly managed.

Overall, I have found molly fish to be a joy to keep as pets.

Their peaceful nature and active personalities make them a great addition to any community tank.

As long as their needs are met, they will thrive and provide endless entertainment for their owners.

Tank Mates For Mollies

Molly Fish Care

These fish are really easy to care for but here are some guidelines that you should follow:

Tank Size

When it comes to tank size, I recommend getting an aquarium that holds at least 30 gallons of water, but a 40 to 55 gallon tank is more suitable for larger species.

Mollies are active swimmers and need plenty of space to move around, so a larger tank is always better.

A larger tank also means that you can keep more fish without overloading the system.

Water Parameters

Mollies prefer slightly alkaline water, with a pH range of 7.5 to 8.5.

The ideal water temperature for molly fish is between 72°F and 82°F (22°C to 28°C).

A stable water temperature is crucial for their well-being, so it’s a good idea to invest in a reliable aquarium heater and thermometer.

Mollies are normally bred in brackish water in overseas fish farms and because of this they benefit greatly from aquarium salt being added to their water.

Make sure to always use aquarium salt and not normal table salt.

Throw in some after a water change to keep these fish hardy and healthy.

Additionally, they need moderate water hardness, with a general hardness (GH) of 10 to 25 dGH and carbonate hardness (KH) of 10 to 15 dKH.

Mollies breeding

What To Put Inside Their Tank

To create a comfortable and stimulating environment for your molly fish, consider adding the following items to their tank:

  1. Live or artificial plants: They appreciate the cover and hiding spots that plants provide. Live plants like Java fern, Anubias, and Vallisneria are great options, as they can tolerate the alkaline water conditions mollies prefer.
  2. Rocks and caves: Adding rocks and cave-like structures to the tank will offer additional hiding spots and create a visually appealing environment.
  3. A gentle water current: Molly fish are native to slow-moving water, so a gentle water current created by a filter is ideal. Avoid strong currents that may cause stress for your fish.
  4. Substrate: Opt for a sandy or fine-gravel substrate that will not only replicate their natural habitat but also be gentle on their delicate fins.
  5. Lighting: They do not require specialized lighting. A basic LED aquarium light that provides a natural day-night cycle is sufficient.

Tank Mates

When it comes to choosing tank mates for my molly fish, I always look for peaceful and friendly species that can coexist in the same aquarium.

These fish are generally peaceful creatures and don’t cause much trouble, but it’s important to choose compatible tank mates to avoid any conflicts or stress in the tank.

Guppies are one of my favorite tank mates for molly fish.

They are colorful, easy to care for, and have a similar temperament to molly fish.

Both species are livebearers, which means they give birth to live young, and they enjoy the same water parameters.

Guppies come in various colors and patterns, which can add a lot of life and vibrancy to the aquarium.

Another great choice for tank mates is Harlequin Rasboras.

These fish have a silver body with a black patch and orange fins, and they can reach sizes of up to 2 inches.

They are peaceful, friendly, and can coexist well with molly fish.

Harlequin Rasboras are also easy to care for and have a lifespan of around 5-8 years.

Tetras are also good tank mates.

They come in a variety of colors and sizes, and they are peaceful and active swimmers.

Some of the most popular tetra species that can coexist with molly fish include Neon Tetras, Cardinal Tetras, and Black Skirt Tetras.

Tetras are schooling fish, which means they should be kept in groups of at least 6 to 8 individuals.

Corydoras Catfish are another great choice for tank mates.

These fish are bottom dwellers and can help keep the tank clean by eating leftover food and debris.

They are peaceful and friendly, and they can coexist well with molly fish. Corydoras Catfish come in various species and sizes, and they are easy to care for.

Food & Diet

As someone who owns mollies, I know how important it is to provide them with a balanced diet.

These fish are omnivorous, which means they eat both plants and animals.

In the wild, they feed on algae, small crustaceans, and plant matter.

Therefore, it’s essential to provide them with a varied diet to ensure they get all the necessary nutrients.

When it comes to feeding, I recommend feeding them twice a day, once in the morning and once in the evening.

It’s best to feed them small amounts of food at a time to prevent overfeeding and water pollution.

Overfeeding can lead to health problems and foul water, which can be harmful to your fish.

There are many options when it comes to feeding mollies.

You can feed them flakes, pellets, frozen or live food.

It’s essential to choose high-quality food that contains all the necessary nutrients.

I recommend looking for food that contains protein, vitamins, and minerals.

You can also supplement their diet with fresh vegetables such as spinach, lettuce, and zucchini.

It’s important to note that these fish are susceptible to constipation, which can lead to health problems.

Therefore, it’s essential to avoid overfeeding and provide them with a varied diet.

You can also add some aquarium salt to their diet to help prevent constipation.

In summary, providing your mollies with a balanced diet is crucial for their health and well-being.

Feed them small amounts of food twice a day, choose high-quality food that contains all the necessary nutrients, and supplement their diet with fresh vegetables.

By following these simple tips, you can ensure your molly fish live a long and healthy life.

molly fish diseases

Common Possible Diseases

I always keep an eye out for any signs of illness or disease.

Here are some of the most common diseases that molly fish can suffer from:

Fungal Infection and Tail Rot: This disease is caused by too much exposure to uneaten food or high levels of nitrates in the water. It creates an environment where fungus can flourish. Symptoms include frayed fins, white patches on the body, and a loss of appetite.

Ich: Ich is a highly contagious disease that can spread quickly through a tank. It’s caused by a parasite that attaches itself to the fish’s skin and gills. Symptoms include white spots on the body, rapid breathing, and a loss of appetite.

Constipation: Molly fish are prone to constipation, especially if they are overfed. Symptoms include bloating, lethargy, and a loss of appetite.

Molly Disease: This disease is also known as “the shimmies” and is caused by unstable water parameters. Symptoms include a loss of balance, erratic swimming, and a lack of appetite.

Fin Rot: Fin rot is caused by bacterial infections and can lead to the deterioration of the fish’s fins. Symptoms include frayed fins, red streaks on the fins, and a loss of appetite.

In conclusion, being able to identify and treat common diseases is essential for their health and well-being.

By maintaining good water quality, feeding them a healthy diet, and promptly treating any illnesses, you can help your molly fish live a long and happy life.


It is really easy to breed mollies. In actual fact, you don’t need to do anything.

If your tank has male and female mollies then you can expect babies every 30 days or so.

They give birth to live fry so don’t be surprised if you all of a sudden find baby mollies in your tank.

She can give birth to between 20 to 100 babies at a time.

Unfortunately, mollies love to eat their babies so if you are wanting to keep the fry then make sure you have lots of plants in your tank so they can hide away.

The other option is to remove the fry to a totally separate tank or breeding net to keep them safe until they are big enough to join the main community tank.

Fry should be fed a tiny amount of finely crushed flake food a few times a day.

Freshly hatched brine shrimp is also a good option.

Why You Should Consider Molly Fish

I have come to appreciate their unique characteristics and the joy they can bring to any aquarium.

These hardy and easy-to-care-for fish are perfect for beginners and experienced hobbyists alike.

One of the most fascinating things about molly fish is their ability to adapt to a variety of water conditions.

They can thrive in both freshwater and brackish water, and can tolerate a wide range of temperatures.

This makes them a versatile addition to any aquarium.

Another great thing about these fish is their peaceful nature.

They get along well with other fish and are not aggressive. This means you can add them to a community tank without worry.

If you’re looking to add some color and personality to your aquarium, molly fish are a great choice.

With so many different types and varieties to choose from, you can create a beautiful and unique underwater world.

I highly recommend molly fish to anyone looking for a low-maintenance, peaceful, and beautiful addition to their aquarium.

With proper care and attention, these fish can live a long and healthy life, bringing joy and beauty to your home for years to come.


How many mollies should be kept together?

They need to be kept in a school. The ratio should be 2 females for every male. So, the amount of mollies will depend on the size of your tank.

Do mollies produce a lot of waste?

Yes, they produce a lot of waste. The reason is because they love to eat and scavenge the whole time. This results in a lot of poop.

Are molly fish easy to take care of?

Yes, they are easy to care for and are consider a good fish for beginner fish keepers. They are hardy and active swimmers.

Do mollies clean the tank?

Mollies are known to eat algae and will eat any algae that is growing on your tank decorations, plants or rocks.

Do mollies need to be fed everyday?

Molly fish should be fed every day. It is best to feed them in the morning and late afternoon. Feed only enough that they can eat in two minutes. Never overfeed them

Can you put mollies in tap water?

You can use tap water. Just make sure you use a dechlorinator to remove harmful chemicals. Also, test the water in regards to pH and hardness.

Photo of author


Irma Bense is the founder of She has over 42 years of experience in keeping fish.She has kept both freshwater and saltwater fish through the years.She has extensive knowledge in breeding numerous species of fish from Show Guppies, Cory Catfish, German Blue Rams to Apistogrammas.You can learn more about Irma on the 'About' page.

2 thoughts on “Molly Fish: Underrated Gems Of The Aquarium World”

  1. One thing I feel like should be mentioned is that most mollies are bred in brackish water in overseas fish farms and so benefit from aquarium salt, especially if the water is very soft and has a low ph.

  2. Yes, you are right and I totally forgot about that. Thanks for reminding me. I will add that into the article. Much appreciated.

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