Molly Fish: The Complete Guide for Beginners

 The Molly fish is a freshwater fish in the Poeciliidae family. Among the many types of molly fish are the black molly fish, sailfin molly fish, Dalmatian molly fish, balloon molly fish, and lyretail molly fish. Mollies come in a range of colors, including red, white, silver, black, and orange.

Molly Fish: The Complete Guide for Beginners
Molly Fish: The Complete Guide for Beginners

 Due to their ability to adapt to almost any environment, molly fish are popular among beginner aquarists. Mollies are peaceful and get along well with other species, making the fish a good addition to a community aquarium.

This is an informative article. Nodisk One is not permitted to make a diagnosis or recommend any form of veterinary care. If your pet is in pain or ill, we recommend that you take him to the vet.

Molly Fish Facts & Overview

- Scientific name: Poecilia sphenops.

- Common names: molly, Molly fish, short-finned molly, common molly.

- Distribution: southern United States and Central America.

- Size: 3.5–4.5 inches.

- Life expectancy: 3–5 years.

- Color: Blue, white, red, silver, orange, gold, purple, black.

- Diet: Omnivore.

- Temperament: Peaceful.

- Minimum tank size: 10 gallons.

- Temperature: 72–78°F (22–25.5°C).

- pH: 7.5–8.5.

- Hardness: 15–30 dGH.

- Care level: Easy.

- Breeding: Livebearer.


 Molly fish are found in parts of Central America, such as Mexico and the southern United States. Mollies thrive in freshwater environments, but the fish are also common in saline habitats, such as brackish lagoons and ditches. 

 Some mollies live and breed in shallow marine environments, such as harbors and the waters around the roots of mangroves. Mollies are common in the wild. Colorful species of molly fish are bred in captivity, and wild molly fish are a dull silver-gray color.

Adult Size And Lifespan

 Mollies can grow up to 4.5 inches in length as adults. Female molly fish grow larger than male mollies - males grow to around 3.5 inches in length. Males are also leaner than females, while females have rounder abdomens.

 The life expectancy of a fish molly varies by subspecies, but on average, both male and female fish molly live between three and five years in captivity.


 Molly fish are affordable and widely available at pet stores and online. The cost of a single fish molly is $2 to $8, depending on the vendor and the type of molly. You should buy at least four mollies for an aquarium, bringing the minimum total cost to $8-$32. Some vendors offer freshwater starter packs that include mollies, which cost $50 to $100, depending on the number of fish.

  • A variety of mollies, including Dalmatian mollies, silver mollies, balloon mollies, black mollies, and gold dust mollies.
  • Imperial Tropicals is another good fish molly vendor, selling black mollies, marble mollies, sunset mollies, cream Dalmatian mollies, and assorted mollies.

Appearance And Behavior

 Molly fish come in a range of hues, tail shapes, and patterns. The majority of mollies have flattened bodies and short fins, measuring between 3.5 and 4.5 inches in length. Mollies are peaceful fish that hardly ever display aggression when kept in a relaxed tank environment with friendly tank companions.

Colors, Patterns, Fins And Sex Differences

Different types of mollies have different appearances:

- Black mollies (the most common type of molly fish) have all-black bodies and rounded fins between three and six inches long.

- Sailfin mollies have a light gray body with rows of dark gray spots and an enlarged dorsal fin that resembles a ship's sail.

- Dalmatian mollies resemble the Dalmatian dog breed, with rounded fins and shiny, silvery-white scales decorated with black spots.

- Mollies balloons have short, rounded bodies, like an inflated balloon, in colors such as white, silver, black, orange and yellow.

- Lyretail mollies have a caudal fin that tapers into points at the top and bottom, and trails behind the fish as they swim.

 Male and female mollies of various types differ from one another in distinctive ways. For example, the anal fin of a male common molly is long and points backwards, while the anal fin of a female common molly points downwards. In most types of molly fish, males have brighter, brighter colors than females. Mollies fade due to stress, and some molly fish darken or change color or pattern as the fish ages.

Typical Behavior

 Mollies are a peaceful species of fish that get along well with other fish. However, certain triggers make molly fish aggressive, including aggressive tank mates and a crowded tank. As social schooling fish, mollies prefer to be housed in groups of four or more. Buy one male molly fish for every four female mollies in your tank to keep the males from fighting and asserting dominance.

Mollies swim close to the top of the tank because they are accustomed to living in shallow water. As shy fish, mollies prefer lots of hiding places, such as plants and caves, where they can retreat when they feel unsafe. Mollies are diurnal, which means they are most active during the day and sleep at night.

Molly Fish Care And Tank Requirements

 Due to their adaptability and hardiness, molly fish are simple to keep in the ideal tank environment. In the wild, molly fish live in shallow, loosely vegetated surface waters. You should create a similar environment in a planted tank with fresh water. Mollies are omnivores, so they consume small fish, crustaceans, insects, and insect larvae for protein. Fish also love plant matter and algae.

Habitat And Tank Requirements

 Rivers, streams, lakes, swamps, deltas, estuaries, marshes, and shallow surface waters are all places where mollies can be found. Because mollies are adaptable to a wide range of environments, fish can withstand wider temperature and pH ranges. However, you still need to create an environment that replicates the molly's natural environment to ensure the fish thrive in captivity. The foliage in a molly's tank is substantial and the plants can be held in place with a thin layer of sandy substrate.

 Mollies don't spend a lot of time at the bottom of the tank, so you shouldn't worry about them disturbing loose-rooted plants. Tall plants like anubias nana and short varieties like java fern provide shelter and hiding places for fish molly. Rocks and caves provide mollies with a place to escape if the fish are harassed by their tank mates. Mollies are accustomed to brackish water in the wild, but recreating this in captivity is difficult and limits the species of fish that can be considered tankmates for mollies.

Tank Conditions

For molly fish, the following tank conditions are ideal:

- Water type: Hard, freshwater.

- Tank size: 3 gallons for each additional molly fish, with a minimum tank volume of 10 gallons for up to four mollies.

- Water temperature: 72–78°F.

- Substrate: Sand, rocks, pebbles.

- Tank setup: Plants, caves.

- Acidity: 6.7–8.5 pH.

- Water hardness: 15–30 dkH.

- Filter: Yes, to get rid of extra nitrate, ammonia, and debris.

- Bubbler: Yes, to oxygenate water.

- Lighting: Not unless the aquarium is a planted aquarium with little access to natural light.

- Water heater: Yes, to replicate the warm climates that mollies are accustomed to.

- Pump: No, mollies don't require a fast current because they are accustomed to slow-moving water.

 Once you have established the right tank conditions for your fish molly, make sure those conditions are maintained. Use a thermometer to check water temperature and a pH meter to check pH. Properly maintained water parameters will allow your mollies to thrive in captivity.

Common Molly Fish Diseases

Molly fish kept in captivity are susceptible to several prevalent freshwater diseases, including:


 The majority of freshwater fish are affected by the protozoan Ichthyophthirius multifiliis, which causes ich. The disease is characterized by white spots, which look like nuggets of salt, on the fins, body and tail of the fish. Ich makes fish appear drowsy and cause them to rub against rough surfaces. Treat it by moving the affected fish to a quarantine tank, raising the water temperature two degrees, and adding one tablespoon of salt per five gallons of water in the tank.


 Velvet is another common Molly disease caused by a parasite called Oodinium. The parasite burrows into the skin of the fish and produces golden rust-like cysts. Molly fish with velvet will rush from one end of the tank to the other, appear lethargic and rub against rough surfaces. Treat the velvet by turning off the tank lights and adding copper sulfate, acriflavine, or formalin to the tank as recommended by your veterinarian.

Fin And Tail Rot

 Both long-finned mollies and fan-tailed mollies are at risk of developing fin rot and tail rot. This disease is caused by bacterial infection resulting from overcrowding, poor water quality and stress. A molly fish with fin rot will have frayed, ragged, milky colored fins. Perform a complete water change to treat fin and tail rot and use antibiotics if you don't see any improvement in the fish's symptoms within a week.

Molly Fish Tank Mates

 Mollies are peaceful, but the fish show signs of aggression when housed in crowded tanks or with aggressive tank mates. For this reason, you should house molly fish with friendly fish and give them enough space to swim.

 Because mollies enjoy the company of other mollies, you should prioritize buying at least four mollies before considering adding different fish to your tank. Excellent tank mates for molly fish include:

  • Guppies.
  • Danios.
  • Platys.
  • Gourami.
  • Tetras.
  • Angelfish.
  • Swordtails.
  • Certain cichlids (keyhole cichlids, dwarf cichlids, ram cichlids).

Molly fish can also live with non-fish tank mates, such as:

  • Snails.
  • Algae-eating crabs.
  • Shrimp.

Diet And Food

 Molly fish consume small invertebrates and plant matter like algae in the wild. Feed the mollies the same diet in the tank to ensure the fish get essential nutrients from their meals. Algae is a staple in the diet of molly fish, and growing algae in your aquarium is the best way to provide your fish with this food source. Feed your molly fish algae wafers if your tank does not have enough algae to feed all of your fish. Spinach, lettuce, and zucchini are also good plant-based options for fish molly.

 Your molly fish's diet should also include fish flakes and live or frozen foods like brine shrimp and bloodworms to help the fish get a variety of nutrients. Rotate between plant matter, fish flakes, and live food to ensure your molly fish gets all the nutrients it needs. Give mollies a pinch of food twice a day. Do not allow mollies to eat continuously for more than two minutes as too much food overloads the fish's digestive system.

Molly Fish Breeding

 Molly fish are easy to breed in captivity and are a good choice for people new to fish keeping. Mollies are viviparous, which means the females hold their eggs inside their bodies before giving birth to live babies. Take the following steps to breed molly fish:

  1. Choose a suitable man and woman. Molly females prefer to mate with the larger males in the tank.
  2. Put the male and female in a breeding tank filled with 78°F water that is suitable for breeding.
  3. When the male is ready to mate, he will perform a courtship display for the female.
  4. After two days, if the female is still not interested in the male, switch the molly fish for another male.
  5. If the female consents to breeding, the male will fertilize the female by transferring milt into the female's body using his anal fin, known as the gonopodium.
  6. Wait 45 days or more before the woman gives birth. Up to 100 young can be born to molly mothers.
  7. When the female is ready to give birth, she hides in a dark, secluded area of the tank.
  8. When the baby fish are born, remove the parents from the breeding tank and return them to their original tank. This stops the parents from devouring their babies.
  9. Feed the fry powdered fish flakes until the fish are able to eat the same food as the adult mollies, around two months of age.

Molly Fish FAQs

Should You Buy A Molly Fish For Your Aquarium?

 If you already have an aquarium with peaceful fish and the right conditions for mollies, or if you are planning to establish an aquarium with these conditions, you should consider getting a molly fish for your aquarium. If your aquarium is crowded or you have aggressive fish, consider whether molly fish is the right choice for you. As long as molly fish are housed in the right water parameters with the right tank mates, the fish are a fun, colorful, and hassle-free addition to a home aquarium.

Can You Keep Just Two Mollies?

 No, you can't just keep two mollies. Mollies are schooling fish, which means they seek safety and comfort in numbers. While keeping a pair of mollies is better than keeping just one, it's not enough. When there are at least three or four other fish present, mollies feel more at home. Make sure the tank has enough space to hold everyone.

 Typically, a one inch fish requires a gallon of water. On average, mollies reach 3 to 4.5 inches in length, so each fish needs about three gallons of free-swimming space. So a 10 gallon tank should be enough for three mollies to cohabit comfortably.

How Many Mollies To Keep Together?

 Mollies should be kept in groups of at least three or four. Mollies are schooling fish, which means they are more comfortable living with fish of the same species. Although you should keep multiple mollies together, be careful not to overfill the tank. A single molly fish needs about three gallons of water to swim freely, so a 10 gallon tank can comfortably hold a small group of three mollies.

 Also, you should keep more female mollies than male mollies, as male mollies tend to be more aggressive. They may hunt females to mate or even hunt other males to establish dominance. To minimize aggression in your aquarium, try to keep a ratio of three females to every male molly.

How Many Babies Do Molly Fish Have?

 Molly fish have 10 to 60 babies at a time. The number of molly fish fry produced depends on various factors, such as health, age, and experience. In general, experienced mothers tend to have more babies than younger, first-time mothers.

 These babies are usually released after a gestation period of 60 days. After giving birth, molly fish can immediately become pregnant again, even if no males are present in the tank. This is because female molly fish can store sperm for months and use it to fertilize their eggs as often as about every two months.

Why Is My Molly Fish Aggressive?

 Your molly fish is aggressive because it tries to mate. Molly fish mating rituals involve attention-seeking behavior, which typically results in a male molly fish chasing a female around the tank. This behavior usually stops once the fish have finished mating. Also, like other species, male molly fish can sometimes be aggressive towards other males.

 This usually happens when fighting for friends or defending their territories. Molly fish are generally peaceful, but some bouts of aggression may occur from time to time. There are three things you can do to help minimize your fish molly's aggression:

  • Avoid overfilling the tank.
  • Provide plenty of hiding places.
  • Keep more female molly fish than male; a ratio of three women to one man is best.

Do Mollies Eat Their Babies?

 Yes, mollies eat their babies. Mollies are opportunistic feeders, so they will eat anything that can fit into their mouths, including their own babies. In order to protect the baby molly fish, you must isolate the mother just before she gives birth. This way the babies won't be eaten by other fish right after they are born. You can either install a breeding box in the tank or place the pregnant female in a separate tank.

 Put the mother back in the original tank after the baby mollies are born so she won't eat the fry. Take care of baby mollies in their own tank while they are still small. After two weeks, you can put the molly fry back into the main tank, as they have grown enough for adult mollies to not mistake them for food.

 If it's not possible to separate baby mollies from other fish, fill the main tank with extra plants so the fry can hide until they are big enough to defend themselves. Adult mollies may still eat some of the fry, which is why it's ideal to separate baby mollies completely.

Are Molly Fish Easy To Care For?

 Yes, molly fish are easy to care for. Molly fish are hardy and low maintenance, making them the perfect choice for beginning fish keepers. Additionally, molly fish are easy-going and passive, so they can coexist peacefully with other fish in community aquariums. Molly fish need the following elements to survive and thrive:

  • About three gallons of water for each molly fish.
  • Keep them together in a group of at least four.
  • Clean the tank regularly.
  • Provide them with a calm environment.
  • Feed them an omnivorous diet of high quality flakes, live foods and vegetables.
  • Avoid housing them with aggressive tank mates.

Do Mollies Clean The Tank?

 Yes, mollies clean the tank. Mollies are opportunistic eaters, which means they will gladly eat anything that is available to them, including algae. These fish will keep your aquarium relatively clean and prevent algae growth. However, you can't rely on mollies alone to keep your tank clean.

 Even if they reduce the patches of algae considerably, they will not be able to eat them all. Also, due to their large appetites, mollies produce a lot of poop and, at the same time, do not eat fish poop. Therefore, you will still need to clean the tank regularly and change the water weekly to keep the tank clean.

What Is The Lifespan Of Molly Fish?

 The lifespan of fish molly is three to five years. Life expectancies differ between different species of molly, but on average most fish molly can live up to three to five years.

 The quality of care they receive will also impact their lifespan. If you want your molly fish to live long and healthy, here are some things you should do:

  1. Provide approximately three gallons of water for each fish molly.
  2. Keep the mollies together in a group of at least four.
  3. Maintain the correct water parameters.
  4. Perform periodic water changes and tank cleanings.
  5. Avoid keeping them with aggressive tank mates.
  6. Feed them an omnivorous diet of high quality flakes, live foods and vegetables.
  7. Provide lots of plants and hiding places.

Why Do Molly Fish Stay On Top Of The Aquarium?

 Molly fish stay on top of the tank due to disease or poor water conditions. A damaged swim bladder is one of the most common reasons molly fish stay on top of the aquarium. In addition to floating on the surface of the water, fish with damaged swim bladders will also struggle and swim erratically.

 Other illnesses that can cause this behavior include parasitic or bacterial infections, constipation, and bloating. Alternatively, this behavior can also be caused by stress and suboptimal water conditions, such as:

  • Water too cold or too hot.
  • Lack of oxygen.
  • Excess waste in the water.
  • High concentrations of ammonia, nitrates and nitrites.

In Conclusion

 Molly fish care really is a snap. It is one of the most beginner-friendly freshwater fish. There's a reason they're so popular! Low-maintenance fish that look great and put on a show are a great choice for everyone. Enjoyable, stress-free fishing is as good as it gets.

Over time, we will add more species-specific care guides to our site. So be sure to check back soon if you're looking for details on particular molly fish varieties!

Only credible sources, such as peer-reviewed studies, are used by Nodisk One to substantiate the information in our articles.