Molly Fish Care Guide & Species Profile

Most people will have seen a molly fish at one point or another. They are one of the most commonly kept fish amongst fish keeping enthusiasts.

They are perfect for people new to the hobby as they are easy to care for.

As an active and social group, you will see plenty of interesting behaviors and unique personalities begin to develop. They are a simple way to add some beautiful fish to your tank.

Molly fish come in lots of varieties with different colors and shapes. With so many to choose from, there’s one to suit everybody.

In this article, we cover the most popular varieties as well as explain their ideal setups, preferred diet, and much more.

Molly Fish Facts & Overview

Black Molly Fish

Care Level:Easy
Lifespan:Up to 5 years
Size:Up to 4.5 inches
Minimum Tank Size:10 gallons
Tank Setup:Freshwater, planted tank
Compatibility:Peaceful community aquarium

Molly fish, or just mollies, are freshwater fish from the genus Poecilia, in the Poeciliidae family. All the species in this genus are mollies except for the Endler’s livebearer.

There are currently 40 species in this genus, so 39 of them are mollies.

These fish are native to the Americas, but their habitat can vary significantly.

An interesting fact about mollies is that, like guppies, they are livebearers. This means that they hold their eggs inside their body until they can give birth to live young straight into the water.

They are a very popular group of fish. Most species are hardy and easy to care for, making them great for beginners. They work well in peaceful community aquariums. If kept in a healthy environment, a group of mollies will thrive and can live up to 5 years.

It’s rare that you will come across a fish store that doesn’t sell mollies – they are one of the most popular freshwater fish.

Common varieties can be found for $2-$4 per fish, though rarer species cost more.

Typical Behavior

They are a peaceful bunch most of the time but can show signs of aggression when crowded or surrounded by aggressive tank mates. Therefore, it’s important that their tank is big enough, and that they have suitable tank mates (more on this later).

Some people mistake Molly Fish breeding behaviors as signs of aggression. When you have a mix of both sexes, you may spot the males chasing the females. This isn’t aggressive, it is just part of their courtship.

You may see this quite often since Molly fish mate regularly, even in captivity. They are one of the easiest species for breeding at home, so they are great for aquarists who are starting their first breeding tank.

Mollies are active and social so they enjoy schooling together. A shoal should be predominantly female since males are known to harass and stress females.

It’s easy to spot personalities in an active fish like these. Watching them for a while will quickly get you attached as you notice their individual differences.

Types and Appearance

Balloon Molly Fish
Balloon Molly Fish

There are lots of molly fish varieties – most are very similar to the common molly (Poecilia sphenops). The main differences are colors and patterns, but sizes and shapes can differ too.

The common molly has a flattened body. It’s tall in the middle and narrows towards a point at the mouth. At the other end is the caudal fin which is a large fan that can be transparent or colorful.

The dorsal fin can be raised as a fan, resembling the caudal fin, or flatter against the body.

Sexing these fish isn’t too hard and they are easy to mate. Females have an anal fin that spreads into a fan, whereas a male is pointier. Females are larger too, potentially reaching 4.5 inches. Males grow to 3 inches.

Pregnant females will look even larger. Their bellies swell to be much bigger than other females.

Here’s a summary of a few popular mollies for home aquariums:

Black Molly Fish

These fish are black all over. Apart from that, they’re virtually the same as the common molly.

Sailfin Molly

This variety is bred in lots of different colors and patterns. Its most distinctive feature is the large dorsal fin which is taller and runs from behind the head to just before the caudal fin.

Lyretail Molly

Just like the sailfin molly, the lyretail stands out because of its fins, but this time it’s the caudal fin. The top and bottom of the fin narrow into points that trail behind the rest of the fish.

Other popular mollies include the Dalmatian, Balloon, Red, White, and Orange.

Habitat and Tank Conditions

Molly Fish

In the wild, a molly’s habitat can vary. They have adapted to lots of different water conditions, including tolerance to brackish waters and high hydrogen sulfide levels.

They are mostly found in the shallow parts of rivers and streams across North and South America. Here the substrate would be sandy with rocks and debris sitting on top.

Plants would be plentiful too, they mainly use these as shelter but they’re important for reproduction as well. The rivers are in tropical climates so get a good supply of light for plant growth.

The waters would be warm and slow-moving. pH tends towards being slightly alkaline.

Tank Setup

Mollies bred in captivity for the aquarium trade are all used to similar environments, so you don’t need to worry about each variety needing a different setup.

A layer of the sandy substrate along the bottom of the tank is a good idea. Whilst they won’t spend much time down at these levels, the fine-grains are good for keeping plants.

You are free to choose your favorite plants, but taller options like Anubias nana make good shelter for these mid-level swimmers. Use decorations like rocks to create caves and crevices. They’re useful for all fish to get away from others that could be harassing them.

A tropical fish like this needs a heater in the tank to maintain temperatures of 72-78°F. Keep pH between 6.7 and 8.5, and hardness between 20-30 KH.

Some people recommend slightly brackish waters for your mollies. The benefits of this are not confirmed, and it limits the tank mates you can keep with them, so we would avoid this.

Standard aquarium lighting will be enough. You don’t need any other special equipment (like a water/air pump) either. These fish are used to slow-moving water which the filter outlet will provide.

What Size Aquarium Do They Need?

A molly fish needs at least a 10-gallon aquarium. This size would be suitable for up to four depending on the species – larger mollies like the sailfins will need a 30-gallon tank.

Each additional molly will need around 3 gallons to live comfortably.

Tank Mates

Molly Fish In Bag

As peaceful fish, they don’t cause many problems, so they go great with other peaceful species in a community aquarium.

Some good choices include cherry barbs, Corydoras catfish, Danios, dwarf gourami, Harlequin rasbora, Platies, Rosy Barbs, Tetras, yo-yo loaches, and Zebra Loaches.

There are lots more to choose from, most small peaceful community fish will be fine.

Fish to avoid are large or aggressive. Large fish will try to eat your mollies, aggressive ones may attack and stress them out to the point of death.

Unfortunately, this means that betta fish do not make suitable tank mates. They are much too aggressive and will likely harass or fight with your molly fish to the point of death.

Cichlids are a group that contains numerous bad examples. For instance, convict cichlids have an aggressive reputation and don’t play well with others. Some cichlids aren’t a problem though, like Angelfish.

Most invertebrates will be happy living alongside your mollies, they’ll mostly be ignored. Shrimp and snails are popular options, and there are plenty of species to choose from.

Keeping Molly Fish Together

You should keep them in groups of at least four or more, they naturally stick together. The group should be made of mostly females since males are known to harass them. Reproduction is usually the only cause of aggressive behavior.


As omnivores, there are lots of different food types that you can feed them. In the wild they’d eat small invertebrates, but mainly plants and algae. There are many similar foods to give them in an aquarium.

Algae is a big part of their diet, they use their lips to scrape it from surfaces. Vegetation is important too, you can use small pieces of green vegetables from your kitchen. Lettuce, spinach, and zucchini are all good options to drop into your aquarium. You can even use them to make your own homemade fish foods.

Artificial foods like flakes and pellets are an easy option. Try to supplement these with other foods to provide a wide range of nutrients.

Dried foods lose most of their nutritional content during the manufacturing process. A diet formed solely around these could lead to health problems, and it is often the cause of a fish losing its color.

Introducing carotenoids into the diet is a great way to keep your Molly Fish looking bright and colorful. They help to express the pigments across a fish’s body.

Live and frozen foods are excellent sources of protein. Bloodworms and brine shrimp will be happily accepted, but most other options work well too. Live foods are more interesting for the fish come feeding time too.

Feed them small amounts twice a day. This gives their digestive system a chance to process the food. Give them as much as they can finish in two minutes.


Dalmatian Molly Fish

Mollies are some of the hardiest and more adaptable fish out there.

Just like any other fish, the big thing is a clean tank. You need to know how to clean effectively. This includes monitoring the water conditions and checking that ammonia and nitrites are at 0ppm.

Your fish will likely start losing their color, or develop worse health problems if water conditions are poor. Monitoring the water conditions will help you to avoid reaching this point.

Your mollies may develop a condition called “molly disease” (or “livebearer disease”, or “shimmies”). This isn’t actually a disease because it’s caused by poor water conditions.

Affected fish will swim around less, wiggling and shimmying in one spot. Check your water parameters and correct any issues, once conditions return to normal you should see improvements in the health of your mollies.

In addition to molly disease, they can get a range of diseases common in many freshwater fish, such as ich and velvet. Keep an eye on your fish to spot signs of disease.

Common signs include a loss of appetite, inactivity, spots, wounds, and color changes.

Cleaning the tank and switching up their diet are a couple of easy ways to reduce the intensity of the disease. If the problems persist, there are treatments that you can purchase from stores.


Mollies are livebearers, which means their eggs develop inside their body so that live fry can be released. They are one of the easiest fish groups to breed in captivity and will mate regularly.

Conditions in a breeding tank need to be perfect, the water (and tank in general) should be clean.

Raising the temperature slightly could help to initiate mating, but don’t go higher than 78°F. Males perform a courting display for the females, when the female is ready to mate she will allow the male to fertilize her eggs. Sometimes the male tries to “sneak-copulate” where he approaches an unaware female from behind.

Females often choose to mate with the largest males.

After fertilization, it will take 35-45 days before the young are released. Larger females could release up to 100 juveniles.

The young need to be separated from the adults or they will get eaten. One option is to put pregnant mollies in a breeder’s box before they give birth, the young are free to leave the box through small holes but the adults stay trapped.

You can feed them foods like broken flakes until they’re big enough to eat the same foods as the adults. At this point, they can be mixed back in with them.

FAQs on Breeding

Q: What does a pregnant Molly Fish look like?
A: A female’s belly will swell to be much larger than usual. This is generally easy to spot, especially when comparing them to other mollies in the tank.

Q: What do Molly Fish babies look like and how do you care for them?
A: The fry looks like small versions of adults, with large black eyes. Colors will vary depending on the species. Keep the fry separated from other fish (including their parents) until they are a similar size.

Are Molly Fish Suitable For Your Aquarium?

There aren’t many reasons not to get mollies, they are a great choice for community aquariums. You just need to consider whether you have the right tank mates. You need to avoid large or aggressive fish.

Their health is also dependent on the conditions of the tank, which need to be within their preferred range. They can tolerate a wide range though, so they can go in lots of different tanks.

You won’t have a problem with their diet either, they can eat lots of different food types.

Overall, they are very easy to care for if you have the right tank. In return, you get a group of fish that are easy to breed, introduce lots of colors, and display lots of activity.

Molly Fish FAQs

About Robert 420 Articles
Robert Woods is the creator of FishKeeping World, a third-generation fish keeper, and a graduate in animal welfare and behavior. He is also a proud member of the Association of Zoos and Aquariums, the Marine Aquarium Societies of North America, and the Nature Conservancy.


  1. Dale Herrstrom says:

    Just retired at 69 years old and enjoying my aquariums again. I’m interested in a list of plecos that will spawn in captivity and what tank conditions they need to be successful. I’ve had success with albino plecos and would like to try others. Thank you. I enjoy reading your articles as they come on the fishkeeping site. Molly fish are enjoyable and the article was a good basic topic for all fish keepers. Thank you again.

  2. Heather Johnson says:

    I just got m 6 year old daughter a small, 1gal, corner tank with an xs filter. She already has a beta (in a separate tank) so she wanted something different. We ended up getting 2 mollies and a small panda cory for her small tank. But we weren’t informed that they required a heater. We’ve only had them for 24 hours, but now I’m concerned. Is there something I should be doing? Should I be rushing out to get a new tank? Or do I need a heater? Do they even make heaters for a 1 gal tank? I didn’t think that Mollies would be difficult to keep. I’m just not sure what to do.

    • Jess says:

      Yikes. Betta fish need at least 5-10gal to live happy. Its a huge myth that they like tiny tanks. As stated above, a single molly requires at LEAST 10gal. If you have other fish in with them, i cant see them living very long in such a small, crammed tank. I would consider getting a nice 20gal for the community fish, and a 10 gal for the betta since it cannot live with other fish.

    • Heather C says:

      @Heather Johnson
      2 mollies and a panda cory in a gallon tank? That is way, way, way too small of a tank. I can’t really stress enough how too small of a tank that is… hopefully by now you’ve gotten them a larger tank. If not, they’re probably dead or close to it.

    • Ukiah Moon says:

      That tank is way to small for molly fish in my opinion mollys should always be kept in a 20 gallon tank or larger. Also panda corys need to be kept in schools of three. also these are tropical fish so they definitely would need a heater.

    • Simone says:

      Definitely need a bigger tank…

    • Susan Bernal says:

      I really hope you went to the store and got a tank that’s a least 10 gallons and a heater and a lamp

    • Chi says:

      I know it’s knida late for the response…but no you do not need a heater. I have a 3.5 gallon tank and the reproduce just like my 60 gallon tank with a heater.

    • Emily says:

      Man…. that is way way way too small for that many fish. Betas need a heater too. Molliesime to live in groups if 4 or more. You need at LEAST a 10 gallon tank gor all if those fish.
      Betas alone cant even live in a 1 fallon tank. They need 2.5 MINIMUM

    • Walt says:

      U need a bigger tank with a heater and a filter

  3. kelly durfey says:

    I just got my fish today and only have one but want to get more but the people at the store didnt tell me the gender so i dont know what gender fish to get? How do I tell?

    • Julia says:

      If it is a balloon molly or any mollie a boy looks like a hook on the bottom fin and a girls bottom fin is round

    • Ukiah Moon says:

      The males anal fin will be pointed and the females will look like a normal fin. hope this helps!

    • Chi says:

      For a female, the anal fin is shape of a fan and the male is like a pointed stick. Usually the ratio is 4 females to one male so that the female will not be stressed out due to the male wanting to mate ALL the time.

    • Paisley says:

      Hey Kelly!
      I know this is quite a late reply, the female mollies have two fan-looking fins on the bottom. The males have a long-looking fin at the bottom that sticks out. It’s a little harder to tell when they’re younger, though.

  4. Aelishan Shrestha says:

    Why isn’t my fishes(guppy,molly and swordtail fishes) are not giving birth even though they have black spots on their belly?

    • Ann Watson says:

      I have over 200 molly’s under the age of 4 mo. I saved as many as I could but still lost some. Then realized I couldn’t keep them all. I stopped saving them but they also stopped eating their young!! I think I have the most beautiful Mollies, no one wants them. What can I do?

  5. Ukiah Moon says:

    Mollys also can be kept in full saltwater!!

  6. Cindy says:


    I live in Maine close to Canada. I was told I cannot buy Goldfish in Canada because it is illegal for them to enter Maine. Why? Because they are a member of the Cod fish group.
    Are Mollies members of the Cod fish group?

  7. Sydney says:

    Very informative! I’ve had a tank of female lyretail for over a year now, they live peacefully with a corry catfish and a school of neon tetras. The lyretails are mother and 4 daughters and they seem to love being together. I was looking for more information on the live bearer disease as momma keeps lying on the bottom rocking side to side, and tends to sink back to the bottom when coming to the surface. Any ideas on what could be wrong with my momma molly?

  8. Bella Smith says:

    my husband has just got some Black Molly Fish but we do not know what kind of food we should feed them. We are wondering whether we feed them by brine shrimp or bloodworms. Does anyone have experience about this and give me some advice? Thanks!

  9. Rikhin says:

    As we know mollies are good community fish. But silver molly (female) is very agressive. It attacks other fish. While other mollies are coexisting. Any suggestions?

  10. Jan Walton says:

    I have just started a tank, my friend advised me with purchasing mollies and neons plus a plecki. I bought dalmation, plus red/ Blk fin type, and some blackfish which had white eyes and a whitish stripe. These black ones killed all my damations, and ate baby guppy’s, ate half the neons too. My friend had a larger tank with larger fish, and they attacked and killed some of those. They were put in the communal tank areas, but definitely aggressive. Cannot find the name of these . Can u help ?

  11. Ravindran says:

    I want to know a Molly fish after first egg release when the fish can be breed again

  12. Brody says:

    Thank you for the advise, this will really help me in the feature. I am still deciding what freshwater fish to get, but i will keep the guppies in mind ;D

Leave a Reply

Your email address will not be published.