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Molly Fish Beginner’s Guide: Care, Diet, Breeding, and More

Molly Fish Beginner’s Guide: Care, Diet, Breeding, and More

If you’re looking for a beginner-friendly aquarium pet that looks gorgeous, you probably want to consider getting a molly fish. You probably won’t find many bad things about this beautiful and versatile animal!

There is a reason why mollies are one of the most popular fish in the aquarist hobby. They are one the easiest pets when it comes to care. Not to mention just how colorful they are!

But, just because they are easy maintenance doesn’t mean there aren’t some care tips you need to know about.

Here’s everything a fishkeeper needs to learn about keeping molly fish happy: 

Breed Overview

molly fish breed overview table chart

Molly fish (poecilia sphenops) is a small fish originating from Central America, but can also be found in some parts of the Southern United States. They are most common in areas from Colombia to Mexico.

In the wild, mollies typically come in a dull, gray color. However, by cross breeding them with more colorful fish, such as their cousin sailfin molly (poecilia latipinna), breeders have produced various colorful morphs – the most common ones coming in red, black, and yellow.

These fish mostly live in freshwater conditions but can survive in brackish waters, as well. 

They have gained popularity due to their attractive appearance and very easy care. In fact, they are one of the most recommended fish for beginners on most fishkeeper forums.


molly fish in aquarium

While I’ll talk about all the various molly fish types, when most people think of mollies, they’re thinking of a common molly that is red in color. Still, I’ll leave the shade bit for later, when I explain different morphs and patterns.

Mollies have a fairly flattened body and a triangular-shaped head, with a narrow snout that’s pointing upwards. 

While females might look somewhat ordinary – apart from their lovely color – males are easily recognized for their pointy anal fin

Despite what many people think, mollies don’t have a pointed caudal fin. This is, in fact, a swordfish. This fish species is often confused with molly fish, and many breeders have been selling them under the same name. 

However, mollies will never have a pointed tail. They might have a forked one, instead. 

Molly Fish Size

While mollies aren’t the smallest fish out there, they certainly are far from being large. 

In general, males will reach the length of 3.5 inches, while females can grow fairly larger, reaching up to 5 inches in length – although most fish I had never grew longer than 4.8 inches.

Their size and the shape of their tail isn’t the only way to differentiate between genders, as males tend to be skinnier and more torpedo-shaped compared to females.

Also, different types of molly fish might have a different maximum size. While, in most cases, it isn’t entirely clear why this is the case, it’s likely due to selective breeding.

Molly Fish Types

little molly fish in aquarium

It would be very challenging to list all the molly fish types in this article, considering how there are several dozen of them. While many are the product of selective breeding, some are the result of crossbreeding mollies with other fish, such as guppies.

Some of these types and morphs are rather challenging to find. This includes:

  • Liberty molly
  • Amazon molly
  • Yucatan molly
  • Green sailfin molly

Still, to give you an idea of just how colorful this fish species is, I’ll list 7 most common types.

Common Molly Fish

Common molly fish are the most common type of molly. You can probably find them in the first pet store you go into!

They come in single colors that can vary in shade anywhere from red to yellow. Some people consider black mollies to be just another variation of a common molly, but I’ll give you one key difference in a bit.

Black Molly Fish

black molly fish

While black is a rare color for most fish species, it is, in fact, rather common in fish such as mollies or king crowntail bettas.

As their name suggests, black mollies come in a solid black shade – although some might have yellow spots or tips of the fins.

The only other thing differentiating black mollies from standard mollies is that they seem to be a bit smaller. This is likely the result of early breeding practices that kept these pets about an inch shorter.

Also, there are some reports that black mollies tend to be more aggressive than other molly types. However, I am yet to confirm that, as I haven’t seen any behavioral differences between various molly morphs.

Balloon Molly Fish

baloon molly fish
Photo: cana__jb

Balloon molly fish – also known as balloon-bellied mollies – are molly fish with a curved spine that gives them a more rounded appearance. They can come in any color and pattern other molly types might have.

A curved spine is a deformity that, unfortunately, affects their quality of life. While this is a genetic problem, unlike most other causes behind a bent spine, these fish still require some additional attention.

First of all, balloon molly fish might have some swimming issues. This can cause trouble with their tank mates, as they won’t be able to swim fast enough to keep up or run away from them.

Next, these fishies might have coordination problems. You might notice they aren’t swimming straight and that they have a hard time staying in the right direction.

Mollies with a spine deformity are also shorter than regular mollies, and they will rarely grow larger than 3 inches.

Finally, balloon mollies might be more prone to illnesses such as swim bladder disorders or dropsy.

Because of all these problems, balloon molly fish are considered difficult to keep. I would never recommend them to a beginner, as they aren’t likely to live very long without proper care.

Dalmatian Molly Fish

dalmatian molly fish
Photo: aquakolo

Dalmatian molly fishes are somewhat rare, but they seem to be easier to find nowadays than when I was just starting this hobby.

These fish have black spots, just like Dalmatians! Another common trait they share with these pups is that their base color is typically white, although other color varieties exist, as well.

Sometimes, these fish might have spots of another shade, making them tricolor.

Gold Dust Molly

Gold dust mollies are another common color morph that’s popular due to its unique shade. 

These fish come in varieties of yellow with a black spotted tail. Black spots on the head and body are also possible, although not as common. 

A popular variety of gold dusts is a 24-karat gold molly that has fairly noticeable black spots – but they are still there, differentiating them from regular common mollies.

Lyretail Molly

lyretail molly fish

Lyretail mollies are different from common mollies by the shape of their tail. 

Unlike common mollies that have a rounded tail, lyretail mollies have a forked caudal fin. This is where the differences end. 

You can find lyretail mollies in almost all colors of a common molly.

Sailfin Molly

sailfin molly fish

Sailfin mollies, as previously mentioned, are not the same as common mollies. In fact, they are their close cousins.

These fish come in various colors and morphs, but all will have a pronounced dorsal fin in the shape of a sail – hence their name.

Keep in mind that the only way they’ll develop a proper dorsal fin is if they live in a fairly large tank. This is why you might want to keep them in a slightly bigger tank compared to regular mollies.

Temperament and Behavior

In general, mollies are friendly and peaceful fish that will love being in the company of other fish. In fact, they are shoaling fish that should be kept in large groups to thrive and feel secure.

In fact, you’ll rarely see a molly fish swimming alone without the rest of its group. While they are not timid, they will feel much better this way.

However, males might be a bit aggressive during the breeding season, especially if the conditions are right for mating. They might harass females, but this shouldn’t be too stressful for them if the male-to-female ratio is around 1:2.

Males might also try to shoo away other males and fish from females they want to mate with. 

Fortunately, if you provide your mollies with a large enough tank and lots of hiding spots, you will minimize the chances of this naughty behavior.

Health Problems

Most mollies are fairly healthy fish that aren’t prone to any breed-specific illnesses. Of course, this doesn’t apply to balloon mollies, as I’ve already mentioned they are prone to a few diseases. 

However, even common mollies can still get any diseases that tend to plague aquariums, such as fish ich, fin rot, or columnaris.

Fortunately, if you keep your fish in proper living conditions and quarantine any new fish, you’ll greatly reduce the chances of illness.

Molly Fish Lifespan

The lifespan of a molly fish greatly depends on the fish type. For example, a balloon bellied molly will live shorter than a standard molly due to its genetic condition. 

If we’re talking about common mollies, they generally live between 3 and 5 years. Of course, this all depends on the care you provide your fish with. 

Care Guide

molly fish in aquarium

Mollies are easy-going fish that are fairly resilient. However, you should still attempt to mimic their natural habitat to provide them with the best living conditions possible.

They are native to warm rivers and ponds of Mexico but don’t hesitate from entering brackish estuaries. 

As responsible owners, it is our duty to do our best to make them feel at home.

Here is everything you’ll need to give your molly fish proper care.


Mollies are considered to be omnivores. This means they eat both meat-based and plant-based food. 

However, in nature, it seems that mollies prefer to eat algae and decayed plant matter more than they like to munch on small invertebrates. This is why their diet should consist mostly of spirulina and plant-based flakes and pellets

There are plenty of commercial molly foods you can find in stores, as well. While some fish keepers are strictly against it, considering it to be artificial or unreliable, I think such foods are a great choice for beginners as you can hardly go wrong with them. 

You might also want to feed your mollies with some boiled, finely chopped spinach or zucchini. 

Mollies will love to eat algae in your tank. This makes them excellent aquarium cleaners, together with corydoras, snails, and blue dream shrimp. However, you should never count on them to survive on algae only. You still need to provide them with proper food.

Tank Size

Molly fish like to live in large groups. As such, they might not be the best choice for smaller tanks, as these might not be suitable to carry an entire molly fish school. 

In general, the smallest recommended tank size is 20 gallons, but they’ll thrive in larger tanks, as well. 

In fact, larger tanks might give you greater control over water parameters, as it’ll take longer for the water quality to get ruined. Even though these fish aren’t overly sensitive, this is never a bad pro to have.

Water Parameters

As, in nature, these fish are highly adaptable, this also means you don’t have to worry too much when choosing proper water parameters. They can survive in most aquariums, although you should still try to create perfect conditions.

Mollies like warm water, but not as warm as some other tropical fish. Anything between 72°F and 80°F is perfect for them to thrive. Just keep in mind that the higher end of this spectrum might trigger breeding behaviors, but more on that later.

Also, they prefer slightly alkaline water, which is quite typical of most fish that live in brackish environments. Make sure you know how to raise the pH in the aquarium if you keep them, but don’t go overboard! Too alkaline is also not good.

It’s important to keep in mind that, even though mollies are rather hardy, they can still get sick or even die if the water parameters change too much too quickly. This is why you should always keep a testing kit nearby.

Water temperature:Between 72°F and 80°F
pH levels:6.7 – 8.5
Water hardness:15 – 30 dGH


All fish produce waste, and too much waste in your tank will raise nitrite and ammonia levels, which is toxic for all fish. As such, no matter how easy maintenance mollies are, they still need a good filter. 

In fact, as they live in large groups, a filter is of utmost importance. Without it, nitrite and ammonia levels will spike in no time.

It doesn’t really matter what type of filter you use for your molly fish, as long as it works. From sponge filters to canister filters, all have their own advantages. The choice is yours.

The problem might arise only if you keep fry. Baby fish are very small and they can get sucked into most filters. For them, having a sponge filter is the safest choice.

And no – just because you’ve cycled a tank doesn’t mean you don’t need a filter. This is especially the case if you’ve attempted an instant 24-hour cycle

Also, while frequent water changes might help keep your water properly oxygenated, this still isn’t a substitution for a good filter. You’ll only stress your fish out unnecessarily.  

Light Requirements

Molly fish don’t really care about light levels in your tank, as long as it isn’t too dark. They are one of the few fish you can keep with aquarium plants that float and don’t need substrate, as they don’t mind if the light is dim.

One thing you should never do is keep them in direct sunlight. Aquarium fish such as mollies don’t need sunlight to live. Quite the opposite, this might create many other issues, such as algae overgrowth.

While you might think that having a lot of algae is a good thing for an algae-eater, things aren’t that simple. 

Most importantly, algae will lower the amount of oxygen in the tank. As mollies produce lots of waste on their own, this means that water parameters can go crazy in no time! Don’t risk this.


Mollies aren’t bottom dwellers. They don’t care too much about the type of substrate you’ll have, as they’ll hardly have any contact with it. 

However, as they love having lots of plants and decorations in their tank, you might consider gravel or sand substrate. These two seem to truly make my mollies happy. Not to mention how this will make your tank look really pretty!


As these fish might be shy, you need to make sure your tank can help them stay hidden when they don’t feel like hanging out. This includes giving mollies lots of decorations!

Anything from PVC pipes to store-bought decorations will do just fine! You might also want to make them rock caves or any other items they can use as hiding spots. 

In fact, there are many reasons why you should want to give your mollies plenty of good hiding places

Not only will such areas keep your fish from being stressed out, but they can help improve their temper. Sure, it’s not like you need to lower aggression in mollies, but it’s never wrong to want to stay extra safe.

Caves will also help females hide from persistent males and give them a place to rest without disturbance.

More importantly, hiding spots might help keep other, more territorial fish from attacking your mollies. Mollies aren’t likely to claim a specific cave, especially not if another fish is already in it. This can serve as a truce.

Live Plants

Mollies don’t really need live plants to survive, but they’ll love having them in their tank. Plants make fantastic hiding spots, and they’ll make your tank look pretty. Not to mention how they’ll help produce oxygen and regulate water parameters!

Still, things aren’t that straightforward. 

Mollies also love to snack on live plants, especially if they are hungry. This might be troublesome, as your beautiful landscape might quickly get ruined. 

Fortunately, some plants, such as anubias, aren’t a tasty meal for most fish. As mollies aren’t strictly herbivores, they won’t eat plants they don’t like. 

Another good choice is picking one of the fast-growing aquarium plants. These might grow quickly enough to hide any potential damage. 

Molly Fish Tank Mates

Molly fish have many suitable tank mates due to their calm temperament and friendly nature.

First and foremost, you should keep them in groups of 4-6. They will love the company of other mollies and might feel stressed if they aren’t in a group. If you keep a single molly fish, their color might dull out and they can get sick and even die. 

As they aren’t likely to swim to the bottom of the tank, you might be able to keep them with semi-aggressive bottom dwellers, such as red zebra cichlids and juvenile Chinese algae eaters. 

However, as mollies tend to get stressed out when paired with territorial tank mates, this might be tricky. Fortunately, there are plenty of other, safer options, such as:

  • Loaches
  • Guppies
  • Danios
  • Dwarf cichlids
  • Rams
  • Barbs

Despite their mild temperaments, you should not keep molly fish with small crustaceans such as dwarf shrimp or snails. While mollies prefer algae, they won’t hesitate to eat your cherry shrimp!


yellow molly fish

It’s very easy to breed mollies in captivity. In fact, all you need to do is to make sure the water temperature is warm enough (around 78°F is perfect) and they’ll do the rest on their own.

This is also good news for all ethical fish keepers, as you aren’t likely to find live-caught mollies – except maybe for the wild-type molly, but this one is rather rare in the hobby as it is. You can buy your new pet without worrying that you’ll harm the environment!

Most of the time, the females get to choose the male that will fertilize the egg. Typically, this will be the largest male in the group, but this doesn’t have to be the case.

Molly fish are livebearers. This doesn’t mean that they’re giving birth like mammals, though. 

Instead, mollies will keep the eggs inside their stomach until they hatch. Then, she will release the fry that is already fully formed. This usually happens 35 to 45 days after fertilization.

While these baby fish are ready to swim on their own the moment they get out of their mother’s body, they are really tiny. This makes them a tasty snack for carnivorous fish. In fact, it isn’t rare for mollies to cannibalize their own children!

As such, it might be a good idea to keep the fry in a 40-gallon breeder tank until they are large enough not to become lunch.

Generally, mollies aren’t considered good parents. There really isn’t any purpose in keeping the fry in the same tank with their parents, so don’t feel sorry for separating the two. It’s the best choice for everyone.

Can You Breed Different Types of Molly Fish

Breeding different molly fish types is not recommended, as you won’t be able to predict the appearance of the offspring. 

For example, you might think you’ll get a black and yellow molly if you breed two solid-colored fish in the same shades. However, this isn’t how genetics work. 

There are many hidden, recessive genes that might not be apparent just by observing the fish. You are more likely to get ugly-looking morphs than to successfully guess the color of the fry. 

This is why it’s recommended to keep your water temperature closer to 72°F if you keep several types together. 

Of course, if you don’t mind being surprised by the appearance of your new mollies, there really isn’t a reason why you should keep these fish from breeding. The babies aren’t likely to suffer from any health problems, and this isn’t dangerous.

The only exception is breeding balloon mollies with other morphs. The spine defect will likely spread to the offspring, and it might be unethical to allow the bad genes to spread any further. Still, this is entirely up to you. 

Final Word

There is a reason why mollies have been a favorite of many beginner (and even some expert!) fishkeepers. They really help keep the stress out of this hobby!

While some might argue that there are more unique-looking fish out there, nothing can replace keeping a fun fish that you don’t need to worry about. Mollies are just that – relaxed yet entertaining.

Not to mention how affordable most of these fishies are!

Whether you are looking for a fish that will be an amazing first aquarium pet, or you’re just looking to expand your collection with an easy-going animal, molly fishes are for you.