A Complete Molly Fish Care: Description, Care, Tank mates, Breeding

Molly fish are small size topical fish, generally called short-finned molly or common molly. Mollies are one of the most popular livebearers in fish keeping hobby. They give birth to young fry instead of laying eggs. In the wild environment, they are found in freshwater streams, coastal brackish, and marine water of Mexico, Central America, and southern parts of South America. Native species of mollies are dull silvery in color. However, there are three species of molly in which sailfin mollies and short-finned mollies are the most common ones. Whereas the Mexican variety is rare, difficult to breed indoor or in captivity, are challenging to care for. Nowadays, due to crossbreeding in captivity, there is a lot of different species of mollies. Mollies are hybridized with other species in the more colorful, exciting specimen. Almost all other type originates from short-finned mollies or sailfin mollies.

Molly fish are relatively hardy fish and can accept a wide range of water parameter; therefore, are easy to care for. This is the reason; mollies are favorite among beginner aquarists. However, to keep them happy and healthy in your aquarium, you need to provide a specific range of water parameters.

Mollies are somewhat similar to swordtail fish. They have a short and rectangular body, upturned mouth similar to swordtail. Male molly grows up to 8cm while female molly fish can grow up to 12cm. Males are more torpedo-shaped, and female is broader at the rear of the abdomen. Male molly has a pointed gonopodium, modified anal fins for breeding purposes.

In this article, I will be talking about my research and findings of molly fish in general. The book “Molly Care: The Complete Guide to Caring for and Keeping Mollies as Pet Fish (Best Fish Care Practices)

” helped me a lot in my research. It is a book that contains all your answers about molly fish. There are hundreds and thousands of species of molly fish around the globe. And talking about each and every species is a waste of time since, what I found through my research is that all mollies differ only is size and color, but all other information about caring, breeding, water parameter requirements, compatibility are the same.

Origin of Molly Fish

Mollies are originated from Central America to Southern America. These fish are typically found in freshwater streams where it meets the saltwater. They have quite a unique ability to live in both freshwater and saltwater. You can encounter Sailfin mollies in the streams of Texas, Carolina, Virginia, and Florida. Short-finned mollies can be found in the water of Columbia and Mexico, whereas the Yucatan molly or the Mexican variety is only found in Mexico’s Yucatan Peninsula.

Short-finned mollies
Short-finned Mollies
Sailfin mollies
Sailfin Mollies

Therefore, mollies habitat is diversified; you can encounter them in brackish water, salt water, and freshwater of different water parameter i.e., water temperature, pH, hardness.

Molly Fish Description

molly fish appearance


Molly fish are small size tropical fish. They have a short and rectangular body, upturned mouth similar to swordtail. Male molly grows up to 8cm while female molly fish can grow up to 12cm. Males are more torpedo-shaped, and female is broader at the rear of the abdomen.


Mollies are peaceful and can keep them with any non-aggressive fish. Fish like, platy, swordtail, guppy, glowlight tetra, neon tetra, etc. are best as a molly tank mates. Male and female molly live together in a tank without being aggressive to one another or any other fish in the community tank. Molly fish breeds like rabbits in your tank, so if you are planning to make some money out of molly, remember that they eat their fry, so separate them. Molly comes in various sizes and colors. Black Molly, balloon molly, gold dust molly, Mickey Mouse molly, black sailfin molly, etc. are some of the favorite breeds of molly.


Molly fish are sold at a very reasonable price, which makes it an excellent fish for beginner aquarists on budget. They usually cost around $2 to $3 per pair.

Molly Fish Care

Mollies are some of the coolest aquarium fish you can buy. They don’t need a massive tank of high-end aquarium setup. Let’s take a look at some of the most crucial aspects to keep molly fish.

With your proper care, mollies can live up to 5 years. Mollies are rarely aggressive and usually get along with most other tropical fish. Molly fish is the best choice for a beginner. Molly is a hardy fish; they can withstand different environments.

Tank Size:

The first item to check before keeping mollies in your tank is your tank volume. Most of the fish keeper makes a mistake choosing an aquarium. In my opinion, to keep molly healthy and happy, a minimum of the 20-gallon aquarium is appropriate for a small group of mollies. Mollies are very fast swimmer and swim around a lot. Therefore, 30-gallon heavily planted tank would be the best one. A larger tank is better balanced in terms of water parameter fluctuations, so why keep them in a small tank? Let them feel home in your tank. And sailfin mollies grow much larger than short-finned relatives if you are planning to keep sailfin mollies get a much bigger tank, at least 29-gallon aquarium.

Best Aquarium For Molly Fish:

These aquariums come with the whole kit that you will require. However, you will need to buy the stand separately if you don’t have a good and sturdy base of your tank.

For 20 Gallon:

Tetra 20-gallon complete aquarium kit

Imagitarium Newport Wooden Tank Stand – for 20 Gallon Aquariums

For 29 Gallon:

Aqua Culture 29-gallon aquarium starter kit

Imagitarium Brooklyn Metal Tank Stand, 29 Gallons

Water Quality:

The next most important factor is water quality. Aquarium fish are cold-blooded animals; their body temperature depends upon the temperature of the water. The fluctuation in water temperature leads to many fish diseases like fin rot, white spot disease, velvet disease, and fungal diseases, and so on. Likewise, they need a good filtration system to live a healthy life. Let’s look at molly’s requirement to live a happy life in your aquarium.

Water Temperature

Mollies are hardy fish; these fish can adapt quite a wide range for water temperature. However, you need to provide them with the temperature that they feel safe. The recommended water temperature for molly fish is 70 – 80 F (20 to 25 C). As a helping hand, keep an automatic electric heater and a thermometer so that you have an eye on the temperature since temperature fluctuation can cause stress in fish leading to various types of diseases. Buy quality brand heater because they are safer, don’t explode, and reduce your electricity use. Here are the heater and Thermometer I use.

Water pH Level and Hardness:

Molly fish live in brackish water. Fish living in brackish water can tolerate a wide range of salinities and pH. pH varies for different types of mollies where ideal pH for mollies is 7.5 – 8.5. You should change one-third of the water on a weekly basis and change water steadily to keep the changing process less stressful for your mollies. You can add aquarium salt or sea salt to your molly’s tank, ¼ cup of marine salt per gallon of water. And the ideal water hardness of the water should be between 20 to 30 dGH.

Water Filtration

Aquarium Filter Media Type

Mollies are capable of thriving in various water parameters. Although to give them the optimum water quality, a filter is a must. A filter will not only filter your aquarium water but will also help beneficial bacteria to colonize in the filter media. This will help in the Aquarium Nitrogen Cycle. If you ask any professional and experienced aquarists, they will always recommend a filter that has a higher capacity than what you need for the tank. For me, a Canister filter or a sump filter works the best.

For small aquariums i.e., 40-70-Gallon, Fluval’s C4 Power Filter works the best. It will make your aquarium look cleaner as well since it’s a clip-on filter or Hang On Back Filter.

Water Maintenance

No matter what kind of filtration system you use, or how clear your aquarium water is, you always need to maintain your aquarium water and equipment.

Have you ever wonder living in a septic tank?

What will happen to your body if you stay your whole life in a bathroom where you poop?

Will you be healthy?

Can you imagine that situation?

No right?

Then how can a fish live in a tank that is not filtered, nor maintained? Wil that poor fish be happy? This is the reason; you need to maintain your aquarium often. As an aquarium is a closed system, all the bacteria remains in that aquarium unless you… yes, YOU remove them and replace them with fresh water. Without a filter, it’s a pain in the ass to do a water change daily. So get a decent-sized filter so that you don’t need to do a water change daily. However, you need to change at least ¼ of the water every single week. Test the water parameter, I.e., water temperature, pH hardness, ammonia, nitrite, and nitrate.

Buying these test kits separate is as expensive as hell. But it’s like no pain, no gain. As if you want to go to a 5-star hotel and to expect to pay the amount you spend in a café.

If you cannot afford to spend money on your fish, then fishkeeping is not your hobby.

For those who are looking for these test kits. I recommend you to get API FRESHWATER MASTER TEST KIT. I have been using this kit for more than a year now, it’s cheap and has all the kits I need to examine my aquarium water.

Molly Fish Diet

Molly fish are omnivores, so eat all kinds of food in the market. Feeding molly fish is not difficult; you will find a variety of fish food on the web. The only thing I like to recommend is that it feeds your fish variety of food.

Imagine a situation where you are eating the same food every single day. How long can you go for a week? A month? Will you be healthy? No! Because a single food will not have all the nutrients your body needs. Likewise, fish also needs variety in the diet, you need to feed them with a fibrous meal, protein-rich food, carbs vitamins, and you name it. Therefore, feed them a mixed diet, and remember not to overfeed the fish else your water quality is going to degrade. Feed the ma pinch of food twice a day. That will be enough. Here is a list of all the fish food I give to my fish.

Molly Fish Tank Mates:

Livebearing Fish

Mollies are peaceful fish and are suitable for a tropical freshwater community aquarium with small fish. However, they are also known to nip the fins of other fish occasionally in the time of breeding. This is why some of the aquarists prefer keeping mollies in a sing species aquarium. If you are planning to keep them in a community tank, keep an eye on them as they some thine nip fish fin. Mollies are also aggressive when they are kept alone without females, so add a female to your tank to keep their attention n peace in your aquarium.

Molly Fish tank-mates

The best tank mates for mollies are other species of livebearer fish. Fish like guppy, swordtail, platy, and other mollies are great tank mates. Some of the other species like Danios, glowlight tetra, neon tetra, snails, red cherry shrimps, Amano shrimp will do well.

How Many Can Molly Fish Can my Aquarium Hold?

molly fish aquarium

When you are keeping any fish, the first thing you need to consider is the adult size of that particular fish. One inch of the size of fish requires one-gallon of water. Therefore, in the case of molly fish, they can grow up to 4 inches. So, keep four mollies in a 20-gallon aquarium if you want to keep them happy. And a ratio of two females for each male molly fish is always recommended because mollies are hyperactive and will always be chasing female mollies. This will also help you to control breeding.

If you are planning to create great scape in your aquarium with plants, rocks, and driftwood, go for at least 75-Gallon aquarium, this will be large enough for a group of molly fish. Larger tanks help you to maintain the aquarium’s water parameter as the population of mollies increases.

Lighting the Molly Tank

Mollies do not have a specific need when it comes to lighting the molly’s aquarium. However, if you are planning to keep live plants in their aquarium, you need to provide proper lighting to promote the growth of the plants. Therefore, mollies might not need great lightings, but their tank might.

Fluorescent Light Vs. LED Lights

If you are keeping mollies by themselves, a low watt fluorescent light will do fine. A fluorescent light will not only make your tank look good, but it will also save you money. If you are planning to keep live plants, buy a special fluorescent bulb that is designed to promote plant growth. But I will recommend you to buy LED lights because the fluorescent light needs to be changed every six months as they fade away and their spectrum shifts as they age. So get a LED light, they last longer than any lights and consumes far less power than any other lights. Some of them even come with a timer so that you don’t have to switch on and off manually every single day.

How Many Lightings do Molly Fish require?

Aquarium lighting is essential for the proper development of mollies. Lightening helps to mimic your mollies’ natural environment in your aquarium; it helps to regulate your mollies eating and sleeping. Plants require light for photosynthesis. For an aquarium with only your molly fish, you just need the amount of light to see your molly fish. Since low light won’t promote algae growth in your aquarium, you can light your tank for several hours. However, if you are keeping plants in your molly’s aquarium, one to five-watt per gallon of water works the best depending on what plants are you keeping. For an average, you need to light your aquarium for 8-10 hours a day.
It is essential for fish or plants to have schedule lighting, i.e., day and night, as our aquarium needs to replicate the natural habitat as much as possible. If your light does not have a timer inbuilt, you can purchase it separately. This timer costs a couple of dollars and helps so much.

Breeding Molly Fish

Like most of the other livebearer fish, molly fish are extremely prolific breeders. They breed like rabbits are quickly overpopulate your aquarium. Molly fish are known for eating their fry, so it is important to add a lot of plants and hiding places for the fry. I prefer adding a lot of java moss, anubias, and java fern in my breeding tank. If you don’t want to set up a planted tank, the other option you can choose is to separate the fry from their parents. For this, you can separate pregnant molly fish into a breeding tank and again transfer the female molly fish to the display tank. Fry are free-swimming at birth and accepts any food flakes or algae. Therefore, provide them with quality fry food to develop.

Setting up Molly Breeding Tank

Aquarium Fish

I have been breeding mollies beside breeding guppies, swordtail and platy. Setting up a breeding tank is similar to all the livebearers. The main advantage of setting up a breeding tank is that you have all the control of breeding. When I started breeding mollies, I had four mollies; three females and a male. After a couple of months, I had so many of them in my tank, had to sell them to a pet store. And after a couple of months further, I was breeding them for money.

Let’s look at the steps to set up the breeding tank.

Get a Decent Sized Tank

A 20-Gallon aquarium is a suitable sized aquarium. But as you grow the population, you need a bigger aquarium for me; I would purchase at least four aquariums a 20-Gallon, two 75 Gallon, and a 50-gallon.

  • The two 75-Gallon aquarium is for separating the male and female mollies once they reach their maturity.
  • The 20-Gallon tank is for breeding the mollies, I select the best color out of hundreds of my molly and keep them in the breeding tank where they do their job.
  • A 50-Gallon aquarium to transfer the fry from 20-Gallon since breeding pairs always occupy the breeding tank.

Decorate Your Breeding Tank

Here to decorate the tank, I mean to add plants and driftwoods and rocks so that the fry has enough hiding place. Let the tank cycle for several weeks before adding your breeding pair.

Stock Your Tank

The final stage is to add your breeding pair to the tank and let them do their work. Introduce three females to one male.

How do you know if your Molly Fish is Pregnant?

pregnant molly fish

Now that you have set up the breeding tank for molly, let them do their work, and your job is to wait and watch. After several days you will notice some changes in female molly fish. These changes are the sign that your molly fish is pregnant. The following are the signs that your molly fish is pregnant and is about to give birth.

  1. A bright-colored molly will get its color changed to a darker shade.
  2. Another sign in the bright colored female is the appearance of the black line on the lower belly.
  3. The female molly’s abdomen starts to get bigger and swollen.
  4. The dark spot at the back of the abdomen is literally the eyes of all the babies

After you notice these signs, mark your calendar as they will give birth to their fry in 60 days. Once they are ready to give birth, they will give birth to 40-100 fry.

Molly Fish Pregnancy Stages or Cycle

Molly fish are very easy to breed, and most of the time, mollies are already pregnant when purchased at a pet store. There are four stages in the molly fish pregnancy cycle; they are fertilization, gestation period, fry, and adult.


Mollies are livebearers; they give birth to laying eggs. So, the fertilization process happens inside a female’s body. A male molly will inseminate the eggs while they are inside the female. This is the reason you see a male molly chasing female mollies every single time. The female mollies carry her eggs inside her belly until the fry are fully developed and ready to release.

Gestation Period

The next stage is the Gestation Period; the gestation period of a molly fish is around 60 days. Once molly fish is pregnant, they will be giving birth to the fry after 60 days. This is the time when you will notice changes in the female body, i.e., signs that she is pregnant. One of the exciting facts about mollies is that a female molly can store sperm for months. She can even use it to fertilize the eggs without the presence of a male. I also tried this and found out that it was true. She really can get herself pregnant even if there is no male in the tank. I guess I have answered your question on How Long Do Molly Fish Stay Pregnant.

Molly Fish Fry

Molly fish fryIn the next stage, after completion of the gestation period, female mollies give birth to cute little fry. It’s sad that the young ones, even the mother hunts the fry and eat them. Therefore, to eliminate this situation, place the female to a breeding net or a tank to separate the fry from larger fish that might eat them. Once the female gives birth, transfer the female molly fish to the display tank and separate the fry to the fry tank.

Adult Molly

Feed your fry quality food, and they will grow up healthy in no time. It takes around one to two months for the molly fish fry to grow large enough to transfer them to the display tank with other fish. For a fry to reach its adulthood, it will take around 4-6 months, depending upon the food and water parameter you maintain.

A female molly fish can produce over 100 fry in one birth. The breeding cycle lasts around 40 to 60 days. You will notice an increase in belly size and spot when a female is pregnant. Place the female molly in the nursery tank as the male chases around and stress outs female. You can also use aquarium net breeder also. Stress mollies may have more aborted births and stillborn before the birth date. Mother Molly will eat her own young, therefore move her back to other fish. One male for four females is the best combination. More females aid lessen stress by spreading the pressure between several females. You should heavily plant the aquarium providing female mollies and fry with lots of space to hide. Mollies and other tank mates will eat fries, considering them as food. If you want a specific color or new varieties, get selective breeding.

Caring Molly Fry

Molly fry doesn’t get protection from their parents. Therefore, these tiny little fry needs your help to survive.

First of all, you need to separate the fry from adult fish or their parents. I would recommend you to buy a separate tank for the fry to grow. But you can also use a breeding box to separate the fry in the tank.

Feeding Molly’s Fry

I like to feed you molly fry egg yolks and brine shrimp. I just hard-boil the eggs and give the egg yolks a little at a time. Make sure you remove excess and uneaten egg yolks from the tank else, the water might get contaminated, killing all your fry.

Once they are a bit bigger prepare brine shrimp, preparing brine shrimp is very easy, you just need an air pump, a bottle, a light source, and water. Add brine shrimp eggs to the bottle and provide aeration from an air stone, give adequate lightings, and you brine shrimp will hatch the next day.

You can even feed them food pallets and food flakes, crushing them into a fine powder. Like the adult mollies, their fry is also easy to care for and will accept anything you give them. Make sure that you give them very little food at a time twice a day.

Filtration and Temperature for Molly’s Fry

fish tank setup for beginnersA sponge filter is the best filter for your fry’s aquarium. A power filter can suck the fry as they are not strong enough to deal with the water current. A sponge filter is an excellent filter to housing beneficial bacteria that will help in the Aquarium Nitrogen Cycle process. Look after tank temperature in the tank; molly fry requires a tropical temperature between 72 to 84 degrees Fahrenheit. Equip your aquarium with a high-quality aquarium heater. Change the water regularly to make sure your fry is healthy. It will take 1 to 2 months for your fry to grow larger enough to be introduced into the main tank. Fry should be larger than the mouth of an adult molly fish. So keep an eye on their growth. After an introduction to the tank, watch juveniles for a couple of days to ensure their health and safety.

Common Molly Fish Diseases

Something doesn’t look right and take a closer look at your aquarium, your molly is sick, and there are common external signs of illness. Technically, it is not a disease but a syndrome due to poor water conditions.

If your molly is swimming alone from the group, it can be an early sign of disease. In aquarium fish, rubbing up against objects may be a sign of irritated skin caused by external parasites. Crowding near the filter and gasping for air at the surface is gill disease or gill damage by parasites, bacteria, or viruses. The three pathogens cause bacterial infections: Aeromonas, Vibrio, and Pseudomonas. It is difficult to decide which pathogen is responsible. They have similar symptoms like cloudy eyes, bloody patches, decaying or frayed fins, scratching. Sometimes loss of appetite and swollen abdomen can also be a bacterial infection. If bacteria infect your fish, you need to treat the entire aquarium.

The protozoan Piscinoodium causes velvet disease. Velvet is parasitic algae containing chlorophyll. An expert often suggests darkening your tank if your molly shows a velvet outbreak. Chlorophyll requires light to survive. If your molly is suffering from velvet, you will notice clamped fins and small yellow spots. If gills are affected, your molly will be gasping for air.

Velvet has two life stages: a cyst form and a free-swimming form. Starting stage, i.e., infected, is the free-swimming stage. During this stage, the velvet parasites drive itself through the water until it finds a suitable host. Then attach to gills or skin of the molly and form cyst working on releasing 100 of free-swimming piscinoodinium. The release piscinoodinium goes in search of another host, and the cycle begins again. Therefore, velvet is very contagious.

Copper sulfate seems to the best treatment. Be extra careful, overdose with copper sulfate can easily kill or poison your mollies. You should change the water slowly after treatment is complete. But only the free-swimming stage is affected by copper sulfate, not the cyst.

Prevention is Better than Cure

As we know, prevention is better than cure; therefore, taking preventive measures is essential.

  1. Take the best tank size aquarium with heavily planted to avoid stress to your mollies.
  2. Always avoid a sudden change in the water parameter.
  3. Quarantine your new mollies for 40 days, which prevents the spreading of most parasites into the tank.
  4. Purchase your mollies from reliable sources.
  5. Always feed your mollies and its fry quality food available commercially.
  6. Avoid overfeeding and overcrowding.
  7. Do not share equipment like nets between aquariums. If you have to, soak in water above 90 degrees Fahrenheit for about 10 minutes.