Little knowledge about Molly Fish

Molly Fish/ Mollies

Mollies are one of the most commonly kept fish among the fish aquarist. The Scientific name of Molly is Pocilia latipinna/Poecilia sphenops. They are considered as one of the coolest fish to be kept in the aquarium. Because of diversity in the beautiful colors i.e. black, yellow, orange, white etc. they are popular among the people who love to keep fish. Mollies are small in size and tropical fish known as short finned molly or common molly. They originate from Central and South America and found in fresh water streams, coastal brackish and marine water of Mexico. The native species of mollies have dull silvery color. Molly belongs to the live bearer genus which means that they hold their eggs inside their bodies and give birth to the live fry, direct into the water. There are three different species of Molly in which short-finned mollies and sailfish mollies are the most common. The Sailfish Mollies are found in the streams of Carolina, Texas, Virginia and Florida whereas Short-finned Mollies are mostly found in the water of Mexico and Columbia. Yucatan molly are only found in Mexican peninsula Yucatan. The Mexican variety of Molly is rare as they are difficult to breed in captivity and it is challenging to take care of them. Now-a-days large variety of Mollies can be seen as they have been hybridized with other species. More colorful and exciting species of Molly are the result of their crossbreeding in the captivity. In short it can be said that all the other types originates from short finned or sailfin mollies. They have a diverse nature and are able to live in both freshwater and saltwater. They have a peaceful nature and can survive well with other community fish.

credit: Flickr

Why to Keep Molly Fish as the Pet?

Molly is popular and widely spread as tank dwellers. They are best choice for the beginner aquarists as they are hardy, less demanding; require less space to live and it is easy to breed them. They are loved by people because of their peacefulness, unpretentious, endurance, easy breeding and inexpensiveness.

What is the Habitat of Mollies in Wild?

Mollies have a diverse habitat; they can survive well in fresh water, brackish and saline water of different temperature, hardness and acidity. They have been adapted to live in different life condition which made them hardy because of this; it is easy to take care of them in captivity. They are tolerant to the water changes as they live in the varying water conditions. Mollies mostly found in the shallow parts of river where the substrate would be sandy with rocks and debris sat on top of them. There would be plenty of plants which are mainly used for the shelter but they are essential for reproduction as well. The good supply of sunlight is available for the plants to grow. The water is slow moving and warm with the slightly alkaline pH.

How Does Molly Fish Look Like?

Molly fish is a small sized tropical fish that has a rectangular and elongated body which is bit flattened from sides i.e. tall in the middle and narrows towards a point at the mouth. On the other end is the caudal fin which is like a large fan and can be transparent or colorful. The dorsal fin resembling the caudal fin can be raised as a fan or flattered against the body.

What are the Types of Molly Fish?

Molly fish are thought to be a single breed but in fact, they come in a variety of different species. Here is the list of few of different species of Mollies

  • Dalmatian Molly
  • Dalmatian Lyretail Molly
  • Black Molly
  • Black Sailfin Molly
  • Black Lyretail Molly
  • White Sailfin Molly
  • Gold Dust Molly
  • Balloon Molly
  • Marble Lyretail Molly
  • Gold Doubloon Molly
  • Hariquein Sailfin Molly
  • Platinum Lyretail Molly
  • Golden Sailfin Molly
  • Green Sailfin Molly
  • Yellow Sailfin Molly
  • Green Lyretail Molly
  • Black mottled hi-fin Lyretail Molly
  • Black Balloon Molly

How is the Personality and Behavior of Molly Fish?

Mollies are small-sized, active and peaceful fish, so they can be kept with non-aggressive fish in the same tank. These peaceful fish may become aggressive when placed with the aggressive fish in the same tank. Thus it is important to make a careful selection while keeping them with other species in the same tank; it must have the enough space for all the fishes to thrive well. Male and female Mollies can live in the same community tank without getting aggressive to one another. Molly fish may eat up their fry so it is not recommended to keep parent Mollies with the fry or baby Mollies. They are active, social and enjoy schooling together.

What are the Size and Life Span of Molly Fish?

The Molly fish are relatively small-sized fish with elongated body. On average they may grow up to 4 inches or 10 centimeters in size. The male Molly fish may grow up to 3 inches or 6-7 centimeters long and the female Molly fish may grow up to 4 inches at the age of about 6 months. The Mollie’s beautiful fins get their maximum beauty and size during the Second year of their life.

The Mollies are short lived pet and they usually live for the 5-7 years under the right and favorable conditions given to them. One reason for the short life of Mollies is that they are frequently breeding species because of which they don’t live for a longer time.

How to Differentiate Male Molly Fish from Female?

It is easy to differentiate Male Molly fish from the Female Molly fish. Few differences among the both are given below:

  • Male Molly fish are more torpedo-shaped and have bigger fins than female.
  • The male Mollies have pointed gonopodia and modified anal fins which they use to mate with female fish.
  • Dominant male mollies have intense colors and grow larger fins either to impress the females or to show dominance to other males.
  • Female Mollies have bulky figures and they are wider at the rear of the abdomen for breeding purpose.
  • Female have a bulging or lumpy appearance during their pregnancy.
  • Female have shorter fins and the anal fins are triangular in shape.

Which are the Tank mates of Molly Fish?

Not all types of fish can be kept together as they will not be compatible tank-mates because of different reasons which include swimming compatibilities, fragility, clashing aggression levels and many other factors. Here is the list of the species that can be the best tank mates of Molly Fish.

  • Live bearers are one of the most compatible tank mates of Mollies. The unique of the species belong to this group is that they have ability to give birth to live offspring and nourishes young ones inside the egg with in their body before birth. These species have the same aggression levels. Aggressive fish in the tank may hurt the Molly fish. They are competitive and robust fish and prefer to have competitive and sturdy tank mates. The bottom feeders can also make the perfect tank mates as they keep to themselves.
  • Guppy fish
  • Platys fish
  • Swordtail fish
  • Endlers fish
  • Other Molly fish
  • Dianos fish
  • Tetras
  • Snail
  • Shrimp
  • Gourami fish
  • Minnow fish
  • Female Betta fish

Aquarium for the Molly Fish:

Aquarium or fish tank is the right place for keeping your fish pet. Aquarium having beautiful fish and setup nicely is a good addition to your home, work and living places. Some people believes in having a small bowl in order to keep their tiny fish like guppy, but they are wrong as all the requirements of the fish can’t be provided fully in a small bowl. If someone wants to keep his pet happy then they have to replicate their natural habitat within the aquarium so that they may have a comfortable time and thrive well in the fish tank. An ideal tank for the fish must provide the conditions which are closest to their natural habitat. The tank must have the adjusted temperature, balanced pH, good quality filtration system in order to ensure the cleanliness of the tank, have a good heater and thermometer to maintain the suitable temperature range and most importantly the tank must be right-sized so that the specie which is to be kept may thrive well in the tank happily and live a healthy life with the owner. Molly fish is relatively a small size fish and don’t require a tank with a larger capacity to live happily but it is recommended not to crowded the tank with the aggressive tank mates as it may make peaceful mollies aggressive. As Mollies are hardy and are used to survive in the varying habitat it is not difficult to take care of them in captivity. Thus they make the best option for the aquarist who is at the beginning of fish keeping. If you want to keep your molly fish happy then provide them with the right conditions in the tank.

Setting up and Maintaining Ideal Molly Fish Tank:

It is mandatory to give your fish the best conditions, which fulfills all their requirements so that they live well. Mollies are quite small and peaceful fish and they don’t give hard time to their owner for the maintenance of their tank. It is important to give them suitable conditions to live happily. The Ideal conditions for establishing and maintaining the fish tank require the following aspects to be fulfilled.

  • Right-Sized Tank for the Molly Fish

Molly fish is a tiny and small sized fish which grows up to the size of about 4 inches large. Because of their small size they don’t require the lager space to live, according to measurements the minimum tank size for keeping the small tank of mollies is the tank with the capacity of 13 Gallons. As Mollies are active fish and they need little more space to live happy and thrive well so the perfect tank size for Mollies is tank of 26 Gallons capacity. The fish kept in the smaller tank may become aggressive and will not feel good. Another aspect is that the fish grows up to 4 inches and in the crowded tank it will not feel comfortable in a tank of small volume

  • Substrate for the Molly Fish Tank:

Molly fish are the species of tropical fresh water where they have the substrate of sand so it is better to use the substrate of sand in the Molly fish tank. They are peace loving species and like to form schools. They are less messy because of which it is not as such difficult to clean their tank. As they don’t live alone and form school which may make the tank dirty over the period of a week so it is recommended to clean the tank at least once in a week.

  • Filter in the Molly Fish Tank:

Mollies have a diverse nature and are able to live in various water parameters. A filter of good quality is must require in the tank in order to give them the optimum water quality. The filter in the tank not only removes the toxin and waste from the tank but they are also helpful in the colonization of beneficial bacteria in the filter media that is useful for Aquarium Nitrogen Cycle. Sump filter and Canister filter are best for the molly fish tank. It is always recommended to use a filter of higher capacity than the capacity of the tank so that it may not over load the filter and damage it. For the Small aquarium it is good to use the filter with capacity of 40-70 Gallons which can work the best and makes your tank look cleaner. It is better to change ¼ of the whole tank water once in a week and use the good quality equipment to ensure the cleanliness of the tank.

  • Heater and thermometer for Molly Fish Tank:

Molly is a hardy fish and they can adapt to a wide range for water temperature. It is necessary to provide your pet fish the best suited temperature range so that they may feel safe and happy. The suitable temperature range at which mollies thrives well in the tank lies between 70 and 80 degrees Fahrenheit or 20 and 25 degrees Centigrade. In order to keep the water temperature constant you must use a good quality heater along with the thermometer in the tank. Thermometer will help in adjusting the temperature of the tank accordingly as the drastic changes in the water temperature cause the stress in fish leading to the various types of diseases

  • pH Level in the Tank:

We know that the Molly fish live in the brackish water and the species of this water can tolerate a wide range of pH and salinities. Different types of Mollies have varying range of pH tolerance where the ideal pH range of Mollies is 7.5 – 8.5. Fish keeper should change one third of the water from the tank on weekly basis and try to keep the water changing process steady so that it may not stress your Molly fish. Fish tank owners or aquarists can add aquarium salt or sea salt into the Molly fish tank in order to keep the pH of the tank stable. The one fourth cup of marine salt should be added per Gallon of water. The ideal water hardness in the tank water should be between 20 to 30 dGH.

  • Plants and Decorative in the Molly fish Tank:

Mollies are the small fish and they require the presence of places to hide among themselves in order to feel comfortable, or protection against becoming the food of the larger fish which feeds on the smaller fish in the habitat. Beside this all it is also important from the aspect that the fish should be given the habitat closer to their natural surroundings. It is the better option to have thick plants in the tank as Molly fish mostly like to scrap algae from tank plants. The Molly fish spend most of their time in the upper and middle water layers so decorations and plants should be placed in the way that give the space to swim as well as hide from the predators. Open and well lighted areas are preferred by the Molly fish in the aquarium as in their natural habitat plants have a great exposure to the direct sunlight. Snags, stones, driftwood, large and small leaf plants and decorative should be present in the tank in order to provide the fish with the shelter, if they need to hide themselves. Plants with large groups of leaves work best in the tank. Presence of light in the Tank is beneficial for the growth of algae in the tank.

What Does Molly Fish Eat in Wild?

In the wild Molly fish are mainly Omnivore in nature which means that they can eat both plants and animals. They feed on algae, plant matter and small invertebrates (insects/larvae) they find in their habitat.

What Does Molly Fish Eat in Captivity?

In the captivity, Mollies should be fed good quality flake food and a variety of vegetables. The favorite vegetables of Mollies include cucumber medallions, shelled peas, spinach and zucchini medallions. A spirulina based flakes or pellets can be used as an alternative to plant matter in their diet. These vegetarian creatures like to have addition of protein based food in their diet.

The additional food which can be given to Mollies includes: frozen krill, frozen mosquito larvae, Daphnia, Brine Shrimp, frozen bloodworm, black worm and others.

What is the Amount and Duration of Feeding Molly Fish?

It is an amazing fact to know that the Mollies have teeth and they chew food because of fish they keep hungry and can do anything for food. Mollies even keep on chewing plants and vegetation in the tank, you will find them always looking for the food. They often found eating spitted food even though they are full.

Mollies should be fed 1 or 2 times a day. If you are feeding them the flakes, crumble the fish flakes into small bits so that they can eat easily. Mollies usually take 5 minutes to eat, if you keep on dropping food into the tank, they won’t stop eating. When the Molly fish start spitting out the food this mean that they have had enough of food now and it is the time to stop feeding them. Further addition of food into the tank will end up setting at the bottom and making real mess in the tank.

What are the Common Diseases of Molly Fish?

Mollies are usually less prone to diseases as they are hardy in nature and have strong ability to tolerate. Here are enlisted few diseases which affects the Molly fish.

  • Velvet Disease :


  • Stress
  • Poor water quality
  • Introduced new infected fish


  • Difficult breathing
  • Clamped fins
  • Fish start rubbing against the wall and objects
  • Fish appears to have a slimy film on the body


  • 100% water change
  • Improving tank conditions i.e. wash gravel and rinse filter properly
  • Ich / White Spot Disease:


  • Stress
  • Introducing new fish into the tank
  • Poor water quality
  • Parasite


  • Loss of appetite
  • White spots on the body of fish
  • Fish rubbing the body against walls and objects in the tank
  • Difficulty in breating
  • Fish lies on the bottom of the tank


  • Formalin (Formaldehyde)
  • Raise the temperature of the water to 75-80 degrees Fahrenheit
  • Salt
  • Fin / Tail Rot Disease:


  • Bacterial infection
  • Poor water quality
  • Stress
  • Sudden changes in water temperature


  • Lethargy
  • Loss of appetite
  • Slimy or milky appearance of the fins or body
  • Fins/tail appeared torn or raggy


  • Chloramphenicol
  • Wash gavel, rinse filter properly and check water pH
  • 100% water change
  • Aquarium Salt
  • Dropsy:


  • Kidney issues which may occur due to bacteria, parasite or renal failure
  • Exposed to low water temperature for a long time


  • Uncontrolled or erratic swimming
  • Fish appear bloated and enlarged
  • Eyes begin to bulge out
  • Swollen abdomen
  • Loss of appetite
  • Scales protruding outwards


This is a fatal disease and is untreatable.