Molly Fish (Poecilia sphenops) is a famous livebearer fish commonly available in the aquarium trade. This fish is without a doubt one of the best beginner fish. They are small but hardy fish that can live in harsh aquarium conditions. They are also available in many different colors and fin patterns which makes them desirable fish for any tank setup.
They’re low-maintenance species, making it easier for beginner aquarists to keep them happy. However, this doesn’t mean they are bulletproof species and can tolerate any toxic conditions. Having a strong base knowledge of fish keeping and also care guides for this fish will help you keep your mollies happy and healthy.
So we prepared this care guide to help you fully understand the Molly Fish. We will walk you through all the needs this fish has and will also give you tips and tricks to care for and make fish keeping easy!
Species Profile & Overview
Molly fish are native to Central America. They are often found in Mexico and southern parts of the United States. But there are traces of this fish in Guatemala, Nicaragua, and Colombia.
Mollies are freshwater species but they can also tolerate brackish waters. They are commonly found in freshwaters in Mexico where less brackish water is found in nature. As they spread towards Colombia they got exposed to coastal areas where the water is brackish.
Mollies are hardy species that are designed to adapt to any aquarium conditions. The majority of the mollies available in the aquarium trade are captive-bred. These captive-bred specimens are line bred to become more colorful and beautiful than wild specimens.
Mollies have a lot in common with Platies, Mollies, and Swordtails. They are live-bearing species that give birth to live fully developed fry. However, mollies are slightly larger and hardier of the bunch.
In the wild, mollies live in warmer waters that are well-oxygenated. They also prefer slow-moving waters that are well-planted. Recreating such an environment in your tank gives these fish the best chance to thrive.
These fish are considered beginner fish, but their beautiful coloration encourages many expert aquarists to keep them in their tanks. These fish are bred to develop beautiful patterns and colors that make them desirable for any aquarium enthusiast.
Appearance & Types
The common Molly looks very similar to platies and swordtails, but mollies have slightly bigger bodies with triangular-shaped heads.
Nowadays, Molly fish come in a wide variety of colors, fin shapes, and body patterns. They usually have flat bodies with short fins. Except for the high-fin variety that has a very large dorsal fin.
Same as many other livebearer fish, differentiating the gender of a Molly fish is very easy. Females are often bigger and rounder compared to male specimens. But the easiest way to identify the gender of a molly fish is by looking at its anal fin.
The anal fin in males is pointy and doesn’t fan out. Females have a short and round anal fin that acts as a normal fin on their bodies.
Generally, male specimens are more colorful and vibrant than females. But this can be deceptive as they can get duller if they are under stress. At the same time, these fish have been line bred for many generations so that now both males and females can develop the same colors and patterns.
Molly fish grow to about 3 inches long. However, some individual specimens can even grow to 4 – 5 inches. This highly depends on the genetics of the fish and the quality of life it lived. So don’t expect all your mollies to grow this large.
Males are often smaller than females and have flat bodies. Females are also usually more plumbed with a thicker abdomen area.
On average, molly fish can live for three to five years in captivity. However, keep in mind that many outside factors can affect the lifespan of this fish.
Things like the quality of food, quality of water, and genetics of the fish have a direct impact on the exact lifespan a specific fish might live. That said, some mollies can live well beyond 5 years when kept in optimal conditions.
To ensure your fish can live a lengthy life, you must focus on providing them with regular water changes. The food you feed them should also have high quality but you should never overfeed. More on this later in this guide.
Behavior and Temperament
Molly fish are generally very calm and peaceful species. But there are times that you might see your molly fish act aggressively. This can happen when too many fish are kept in a smaller tank and you have added a few aggressive tank mates.
Mollies are considered schooling fish, but they don’t school tight. Their swim pattern is more like a tight social behavior. Some variants are showing signs of schooling while others might not show any signs of schooling.
The tank setup and size also have a direct effect on the schooling behavior of this fish. When you keep a large number of mollies in a large aquarium then it’s easy to see them all swimming together in a school.
These fish are very active and will swim nonstop. They are often in the middle and upper sections of the tank. But can also explore the bottom of the tank looking for food.
The males also need to have access to more females to prevent aggression. So for every male, you should have at least 2-3 females. Having more females will calm the males down and they will not pick fights over females or chase females to mate.
Mollies are hardy fish and can tolerate a wide range of water parameters. However, creating the right tank environment will let them thrive and live healthier lives.
Recreating their natural habitat is the best way to keep them healthy long term. These fish are used to warm tropical waters and require a clean environment. Their natural habitat of mollies is also very well planted and has many different natural food sources for them to feed on.
In the next few sections, we will explain how you can achieve a similar environment in your tank so your fish can thrive. We will walk you through all the information you’ll need to give your mollies the best possible life.
Mollies are small species but some specimens can grow larger. They are also slightly aggressive compared to other livebearer fish. So the minimum tank they need is 10 gallons. In a ten-gallon tank, you can keep up to 3 mollies.
The best combination for this fish is to keep one male and 2 females in a tank of this size. However, if you want to keep more mollies you will have to invest in a larger aquarium.
To see the true nature of this fish we recommend getting a 50-gallon tank and adding 10 or more mollies. These active fish will constantly swim in a school in your larger tank. A tank of this size will also house more beneficial bacteria to keep the tank cleaner for your fish.
What To Put In A Molly Fish Tank
This fish isn’t picky about its surroundings and will do OK in any aquascape or tank. So this is the area where you can fully articulate your creativity.
That being said, you need to be cautious of the types of decorations you want to use. Artificial decorations can be a good choice as they won’t alter the water’s chemistry. But they lack the natural beauty of live plants and rocks.
We strongly encourage you to use only natural decorations to decorate your aquarium. With natural decorations, you can create fascinating natural-looking aquascapes. At the same time going all natural can make a better and healthier living environment for your mollies.
Live plants, driftwood, and aquarium rocks are all great items to decorate a tank with. Your main focus should be on placing lots and lots of live plants in your tank. Mollies love to live in planted aquariums.
Live plants will also help your molly tank to hold more stable and clean water parameters. They will constantly filter out the waste in the tank. This will keep the water clean and as a result, your fish will stay healthier.
The other benefit of live plants is that they can help newly born mollies survive. As we mentioned mollies will eat their fry so newly-born fries need to have a place to hide. By placing densely grown plants, you can expect a greater percentage of your Molly Fish fry to survive.
If you are new to plant keeping we recommend easy plants like Guppy Grass, Water Sprite, Java Moss, Hornwort, and Moneywort. These plants can survive in harsh conditions and do not need planted substrate.
A planted substrate will be necessary if you choose root-feeding plants. We prefer to add black-colored substrates to our tanks as they look much more beautiful with green plants and our colorful mollies.
Mollies are hardy and adaptable fish but they can be sensitive to fluctuations in water parameters. These fish are one of the hardiest types of fish you can own. But this doesn’t mean you can keep them in poor water conditions.
The best approach to setting water parameters in a molly tank is to recreate the natural parameters they have in the wild. These fish need a slightly warm tank that replicates the weather in their natural habitat. The water also needs to be super clean and well-oxygenated.
Keep in mind that warmer water means more active fish and that means they need more food. Feeding heavily can easily pollute the water so make sure to only feed once or twice per day. They should only receive enough food that they can eat within 2 – 3 minutes. Never leave any uneaten food in the tank to rot.
The water current in the tank is also important. Mollies prefer to live in still waters so you should not add any internal filters or powerheads to your tank. An ideal aquarium for a Molly Fish is an aquarium that it doesn’t have to waste energy fighting with the currents.
Mollies live in a diverse range of water parameters in the wild. They also live in brackish areas so they are perfectly able to tolerate some salt in their tank. Salt also helps them to keep their muscle intact and prevent diseases.
Considering all the key points we mentioned, here are the ideal water parameters you can keep Mollies in:
- Temperature: 75 – 80 Degrees Fahrenheit
- PH: 7.0 – 8.0
- TDS: 100 – 250 PPM
As long as your water parameters remain in the range mentioned above your mollies will thrive. The most important thing is to keep the water stable with no quick fluctuations.
Mollies prefer natural sunlight. In the wild, they live in shallow waters where sunlight can easily penetrate the water. Having a strong light will give them a sense of being at home.
These fish also develop better coloration when kept outside under direct sunlight. However, this is probably not possible for most of us who live in colder areas.
The good news is that most planted aquarium lights are full spectrum and can be great for a molly tank. A full spectrum light will bring out the true beauty of your molly fish and is highly recommended for plants. So we strongly recommend investing in a good aquarium light.
Your light should be on a timer to turn on and off at specific times. Having the light on a timer will make the mollies and plants adjust to a natural day and night schedule.
A good filtration system is necessary for these fish as they can produce a lot of waste. A good filter is a filter that can keep the water clean and process the fish waste quickly. Strong biological filtration is the most important part of keeping mollies.
Most Filters are great for Mollies but you should prevent internal filters that have a strong powerhead. Mollies don’t like fast-moving waters.
Common Diseases and Prevention
Mollies are very fragile when diseases spread in a tank. They are at risk of contracting almost all aquarium diseases. So it’s important to follow the basics of fishkeeping to prevent the disease from being introduced to your tank.
Some of the most frequent diseases seen in Mollies include bacterial infections, fungal issues, and parasite infestations. These diseases are usually introduced by sick fish to a tank and get triggered by poor water conditions.
More specifically, mollies are at risk of developing Ich, swim bladder disorder, and fin rot. These diseases are often caused by excessive stress levels. Low water quality is another major contributor to the spread of several illnesses.
Each new fish you add to your aquarium can bring pathogens into your system. So you should always quarantine new fish for two to six weeks before adding them to your aquarium. Regular water changes will also keep the water stable and can prevent diseases and worms.
Diet and Feeding Requirements
Molly fish feed on small invertebrates and plant matter. They also eat low amounts of algae but you shouldn’t expect them to clean all the algae in your aquarium.
To make it simple, they are not picky eaters! You can feed them any available food and they will happily eat it. Mollies are omnivore species so they will eat almost anything that fits in their mouth.
Fish flakes, pellets, bloodworms, and brine shrimp are among the favorite types of food you can give them. Their diet should be mainly plant-based and high-protein foods like bloodworms and brine shrimps should be given as snacks.
Depending on the temperature of your tank, you will want to feed your mollies once or twice a day. You should only feed as much as they can eat within 2 – 3 minutes. Never let food sink to the bottom of the tank as it can get stuck in between the cracks and start to rot.
Mollies are great hunters and will catch any small creatures that wiggle in the water. This includes insect larvae, worms, and even their own babies. Giving your fish a diverse diet is the best way to keep them happy.
Flake foods and pellets are one of the best commercially made foods you can give these fish. These foods are designed to provide most of the nutrition your fish need and are often easier for the fish to eat. It’s best to have a few different types of these foods so your fish can get all the nutrients it needs.
You can also feed them fresh vegetables like cucumber, spinach, carrot, zucchini, and sweet potatoes. You can cut thin slices of these fruits and boil them just enough to become soft so your fish can eat them. When you first add fresh vegetables your fish might not recognize them as food. So if they don’t eat it, just wait, don’t feed them anything else as they will never eat fresh vegetables when high protein foods are available.
Like all livebearers, Mollies are super easy to breed. Just by having a few males and females in a tank, you can expect to get some breeding activity. However, not all the fry might survive as these fish will hunt and eat their fry.
To ensure a high number of hatched fry can survive, you must separate the female or add a lot of live plants to your tank. It is best to separate the female and place it in a breeding box if you have one available. These breeding boxes are specially designed to separate the mother from the fry so a higher number of fry will survive.
You can also add a lot of densely grown plants in your tank if you don’t have a breeder box. Live plants will protect the fry from adult fish. Any densely grown plant can make a good job of protecting the fry, but our favorite plants are Guppy Grass, Water Sprite, and Hornwort.
A female Molly can breed almost every month and each time she can give birth to 40 to 100 tiny fry. The fry is fully developed into tiny mollies right after birth.
Feeding high-protein food to your Mollies will encourage them to reproduce more frequently.
Mollies are peaceful species and can live with most small and similar-sized fish. But they tend to show aggressive behaviors when the tank is too crowded. At the same time, because of their small size, you should not keep any large fish in their tank.
Mollies will also eat any small creature that fits in their mouth. So your only options are to keep them with similar-sized fish unless the bigger fish are super peaceful!
Considering these points, here are a few of the fish and inverts you can keep with your Molly Fish:
- Freshwater Snails
- Platy Fish
- L397 Pleco
- Bristlenose Pleco
- Other Types of plecos
- Neon Tetra
- Most Gouramis
- Bamboo Shrimp
- Vampire Shrimp
Mollies are one of the easiest fish to keep and breed by beginner aquarists. These fish are fun to watch and are very low-maintenance fish. This makes them a desired fish for many beginner and expert aquarists.
These hardy species of freshwater fish are very smart and can recognize you. There are many color fin variants of them now available which makes them very diverse and beautiful. We highly recommend this fish if you are thinking about getting some.