FIA is community supported website. When you purchase through links on our site, we may earn an affiliate commission. Learn More.

Molly Fish Profile, Types, Care, Tank Setup & Breeding

Molly fish is one of the most popular freshwater fish adopted by hobbyists around the world.

They are easy to provide for, extremely peaceful, and don’t require much maintenance. It makes the them perfect for beginners who are new to the hobby.

They’re extremely social creatures and will develop unique personalities and interesting behaviors.

In this article, we’ll provide you with in-depth care instructions for mollies, the ideal tank setup, preferred diet, breeding, and a lot more.

Species Overview

Level of CareVery easy
TemperamentVery peaceful
AppearanceVaried appearance
Life ExpectancyLive for over five years
SizeMax 5 inches
DietMeat and vegetables
Tank Size10+ gallons
Tank EnvironmentFreshwater with caves and rocks
Tank MatesVery peaceful fish

Mollies (scientific name: Poecilia Sphenops) belong to the Poeciliidae family and are classified as freshwater fish. Except for the Endler’s livebearer, all species in this genus are mollies. There are 39 subspecies, all of which have different colors, shapes, sizes, and behaviors.

These are mostly native to American waters and live in varied habitats.

Like guppies, mollies are livebearers, and pregnant ones will store their eggs inside their bodies until their eggs are ready to hatch straight into the tank.

Most Molly species are exceptionally hardy and don’t require special equipment for survival, making them ideal for beginners.

They live in communities and don’t attack other fish.


Mollies can be found in plain dull colors as well as extremely bright colors.


They can grow up to 5 inches and bring color to your Aquarium.

Females are larger and will reach a maximum size of 5 inches. Males are much shorter and may only get 3 inches.

A pregnant molly fish will grow even larger as their bellies swell in size to accommodate their eggs.


Molly will have a flat body. They are long in the middle and narrow towards their mouth.

At the tail end is the caudal fin, a large fan that can be either colorful or transparent. They can raise their dorsal fin as a fan, which closely resembles the caudal fin.


There are differences in the life expectancy of molly species, but they are known to live for around 3 to 5 years.

You can maximize their lifespan through proper care and attention.

Behavior & Temperament

Mollies are social and active creatures that enjoy schooling together.

The ideal Aquarium will have more females than males at a ratio of 3:1. It is because males will chase around females and stress them out. More females will not curb this behavior, but it will spread the tension equally among other females.

It is a very peaceful species but may show signs of aggression in an overcrowded tank or surrounded by too many aggressive fish.

It is really important to ensure that the tank is large enough and that their tank mates are compatible with them.

As social creatures, you will notice mollies develop unique personality traits in the tank. It can be addicting to spot these differences as you become aware of them.


Although you won’t find them easily in the wild, you can easily purchase a group of mollies from pet stores because they are the most popular freshwater fish ever.

Commonly available ones, such as the black molly fish, can be purchased for as little as $3 per fish. Rarer species may cost a lot more.

Types of Molly Fish

Below are a few of the more popular mollies:

Lyretail Molly

Balloon lyretail molly

Their most distinguishing feature is the caudal fin which has a unique shape – the bottom and top of the fin narrow into tiny points that trail behind the rest of the Molly.

Sailfin Molly

Sailfin molly

These fish are a result of extensive selective breeding to produce vivid color patterns.

Like the Lyretail molly, their most noticeable feature is the large dorsal fin which is longer and goes from behind the head to before the caudal fin.

Black Molly

Black molly

The black molly fish has a skin condition known as melanism, which gives it a completely black appearance.

You may find streaks of silver or yellow running down the dorsal fin or on the flanks in some cases.

Tank Requirements

Your goal should be to mimic Molly’s natural habitat in the tank to maximize their rate of survival and lifespan.

The waters should be slow-moving, and warm. The pH should be just a little alkaline. If you don’t meet the recommended community aquarium conditions, these can easily become sickly, stressed out, and even die

 Some members, particularly the black molly fish, are the most delicate of livebearers. If the right environmental conditions are not met, they will develop a disease commonly known as ‘shimmies.’ More on that later.

The good news is that they are hardy fish that can thrive in a wide range of conditions. They can even live in brackish water conditions with high levels of hydrogen sulfide. Just make sure to add a substrate layer (ideally with sand) at the bottom of the tank.

While mollies are not known for spending too long near the bottom, a well-established substrate can provide a place for keeping plants.

You can choose your favorite varieties when it comes to plants, but the best option would be something taller like the Amazon Sword, Java Ferns, and Hygrophila. Taller plants provide a good amount of shelter to mid-level swimmers.

Tank Setup

  • Tropical freshwater fish like this needs to be kept at a temperature of between 71 to 80° Fahrenheit.
  • Keep the pH slightly alkaline at around 6.5 to 8.7 pH, and the water’s hardness levels should not exceed 30 KH.
  • To make your Molly feel more comfortable, choose at least a 25-gallon aquarium that can provide enough growing room for fry (although there won’t be much of those to worry about).
  • It is best to go for a really large tank (50-gallon or more) to prevent unnecessary aggression or harassment.
  • Although these are not known for being untidy, it is recommended to change 33% of the water every week.
  • Mollies are known for feeding on their fry, so it is important to give them a place to hide. Plants are a good spot as any for fries to hide.

They love to move around, and should you decide to keep them in larger groups,

Some aquarists report that mollies thrive in heavily filtered tanks, although they can live in various environments. To give them a high quality of life, make sure to provide them with high water filtration.

Pro Tip: Do not create disturbance in the water while you change it to minimize your mollies’ stress.

They can be a little sensitive to water parameters once they’ve adjusted to them. It is extremely important to keep the water’s parameters consistent without causing undue stress to your Molly.

They love a well-decorated aquarium, so the more plants you have, the merrier.

Tank Mates

Golden black molly fish pair

The molly fish is relatively peaceful and won’t run into any problems with its tank mates.

Just make sure only to select compatible fish that are known for their passive natures. Avoid aggressive species like Oscars.

As a general rule of thumb: avoid larger or aggressive fish because they will either eat your mollies or attack and stress them to the point of illness and even death.

Some good tank mates include

Mollies like to stick together, so make sure you have at least 4 in the tank. Adhere to the 3:1 female to male ratio to avoid male aggression.

Food & Diet

As omnivores, Mollies are very easy to provide for and will eat all kinds of foods. In their natural habitats, their preferred diet involves plants and algae,

but they may eat small insects from time to time. You can easily recreate these conditions in the Aquarium. Algae form the bulk of their diet. Mollies will scrape algae from surfaces using their lips.

As just as important, small pieces of vegetables use a combination of lettuce, zucchini, and spinach. Prepare a batch of small vegetables and drop them in the tank. Mollies will start nibbling away at them.

You can either prepare food at home or buy pellets and flakes from pet stores. Make sure to supplement these with other foods to keep them nutritionally satisfied.

Frozen and live foods make for a great source of meat. Some examples include brine shrimp and bloodworms, which they will easily gobble up.

Feed your mollies twice a day. Anything too high, and their digestive system will struggle to process the extra food.

As a rule, give them as much as they can finish in under 2 minutes. Clean up any leftover food residue right after to prevent disease and illness.

This practice will ultimately help them stay healthy and ensure your water parameters are not disturbed at all.


As mentioned above, mollies are extremely well equipped to look after themselves and thrive in various environments. However, they are not completely immune to diseases.

A clean tank is a key to their survival. You will have to learn how to clean the tank effectively. It includes monitoring the water’s conditions and checking for nitrite and ammonia levels (they must be 0ppm at all times).

It may be tempting to use tap water, but do keep in mind that some areas include small levels of chlorine that could be enough to kill your fish.

Mollies can develop several diseases, the most prominent of which are shimmies.

This condition is easy to spot and cure right away. It mostly occurs because the water’s parameters are not compatible with Molly’s preferred living conditions.

In addition to shimmies, they can also contract other diseases, including velvet and ich. Make sure to spot signs of diseases and take preventive care as soon as possible.

Clean out the aquarium and provide them with a well-balanced diet to reduce diseases

If the problems don’t go away, you can always purchase treatments from pet stores.

Common symptoms of a disease to watch out for include inactivity, loss of appetite, wounds, spots, and rapid color changes.

Spotting and Curing Shimmies

If your mollies develop shimmies, they will rock back and forth. Their bodies will seem to be shivering.

They will swim around the tank but do not seem to get anywhere. Mollies’ fins will tightly clamp to their bodies.

If you don’t do something soon, they will die. The sooner you intervene, the better.

The first thing you should do is raise the temperature to around 79°. Secondly, add about one teaspoon per gallon of salt to the tank.

Breeding Guidelines

Baby mollies
Baby Mollies

To initiate breeding, you’ll have to create the right conditions in the Aquarium. For starters,

the water should be really clean. Secondly, you should raise the temperature of the tank to about 79°.

As mentioned earlier, males are always chasing the females around for mating. Once the female is ready to reproduce, she will allow the male to fertilize her eggs

Males may try to mate with females when she’s unaware sneakily. Most females have a preference for larger males.

Once the eggs have been fertilized, it will take around 30 to 40 days for the pregnant Molly to release her fry. Larger ones are known to terminate over 100 little mollies at a time.

Fry Care

As mentioned earlier, they are known to eat their little ones.

It is why it is recommended to keep the fry in a separate tank and feed them there until they’re big enough to defend themselves from bullies.

You could also provide fry with a space to hide by adding lots of artificial plants to the tank.

Should feed the fry at least five times a day with baby brine shrimp or powdered flakes. You can diversify their diet with algae and live plants.

Do keep in mind that fry mollies have a very small mouth and have a harder time eating food.

It is better to crush food in powdered form to help the young ones eat their food. Remove the uneaten food from the tank with the help of a net or skimmer.

If you decide to separate the fry from their parents, it is better to find a large enough tank with about 5 to 10 gallons of water to raise the fry.

Young ones are fragile and lack a properly developed immune system, which makes them prone to diseases and death

It is why it is extremely important to keep tank conditions clean and sterile. You will also need filtration to keep the water clean.

Make sure to choose appropriate filtration depending on the size of your Aquarium.

Keep the water at around 79° Fahrenheit with the help of an aquarium heater. To monitor the temperature, install a thermometer at the other end of the tank. It is to ensure you get accurate and consistent temperature readings.

Even though you may have installed a filter, it is just as important to change the water regularly to keep your fry healthy. Borrow some of the water from the parents’ Aquarium. It will help them quickly acclimate to their new home.

Your goal should be to change about 20% of the Aquarium’s water every day. It means if you have a 20-gallon tank, you should remove 4 gallons a day and replace it with 4 gallons of water from the regular tank.

Fry will need about four months to change into adults completely. Babies don’t have well-defined colors, but they will acquire them after reaching adulthood.

Where to Buy?

You can easily buy mollies from regular pet stores at an affordable price. Rarer species may be hard to come by, but you can obtain them from hobbyists in forums and online stores.

Final Thoughts

Mollies are ideal pets for beginners who are still learning how to care for freshwater fish.

You can also experiment with passive fish to create vibrant communities in your tank. You shouldn’t face any problems with diet and tank conditions either.

Mollies are active, live long, and are extremely social creatures – it won’t be long before you’re addicted to them.