Black Molly: Care Guide To Our Peaceful Black Beauty

A Black Molly swimming
By Garrison Hickles Updated

Coming from the freshwater Poeciliidae family, the Black Molly fishes are livebearers and stand out to be one of the best aquarium fishes. These Black Mollies are favourite among the aquarists because these fishes come in mixed breeds and genes as that of the Guppies.

As a fishkeeper, you would surely want to keep your tank lively and bright and trust us, Mollies serve the best. These fishes come in different varieties and they completely come in a varied range of colours. In order to add an aesthetic feel to your home, keep Mollies, especially Black ones.

While we talk of these black beauties, there are a few important features that every aquarist must have a piece of knowledge upon. This would help them to take care of the Black beauty and here we are, to help you update yourself regarding these fishes. The article consists of numerable information about the Mollies like their lifespan, diet, need for water and also what treatment they need during any disease and many more.

Key Specifications of Black Molly

Black Molly fishes are very peaceful and they can stay well with other species.  Let us dig out some key information regarding this species.

Scientific NamePoecilia sphenops
OriginSouthern to the Central United States along with Yucatan peninsula in Mexico. Basically captive-bred.
Lifespan3 years in captivity and 5 years in the wild
Size3.5-6 inches (males are 3.5 inches and females are 5-6 inches)
CompatibilityAny other peaceful species
Tank Size20 Gallons
Care LevelEasy


Being a member of the Poeciliidae family, the Black Molly fishes are completely captive bred. These fishes are not available in the wild and you would really be in trouble if you try to find out these ones in some swamps or river beds. The source of the distinct and vibrant black colour is somehow not known as they are cross-bred between common Molly and Sailfin Molly. Both of them do not have that dark black colouration, which says that the natural black colour of Black Molly is weird. The interesting fact is, this colour comes from melanin make-up. This generates owing to extra amount melanin in their body, which gives them the status that is just the opposite of the Albino.

Origin and Habitat of Black Molly

Though the common Molly species are found native to the Southern United States that goes down towards Central America. Since, the variant of common Molly, the origin can technically be taken as the source mentioned above, however, the Black Molly fishes are found in the aquarium. These fishes are bred by crossing two different Molly types.

The distribution of their habitat is varied as they can live in brackish water. These are generally found in freshwater rivers, though you can sometimes find them in the estuaries containing the brackish or coastal type of water. They live in streams and a common ecosystem of wetlands, swamps and even coastal areas. Though you can find their parent breed in the wild lagoons, in the waters near the mangrove roots and shallow water bodies.

Appearance of Black Molly

The Black Molly fishes look very pretty with their full black colouration. Their whole body is black to its entirety and that is from scales to tail along with the fins. Their fins look round and without any iridescence, their scales look completely flat in colour.


As we get to know from the name, these Black Molly fishes are found black in colour. You can sometimes find the fish in some yellow streaks, that runs down their dorsal fins. In fact, you can find some patches or spots of different colours in their whole body. If closely looked at, there is a silvery colour found on their flanks.


The females of the Black Molly fishes generally measure up to 5 inches while the males are within the size of 3 inches.

Behaviour of Black Molly

The Black Molly fishes are actually calm and tranquil in nature, hence they can be kept with any species that are equally peaceful. However, with aggressive fishes or some larger ones, your Black molly can turn aggressive and restless. In an overcrowded tank, they feel scared and irritated, as a result of which they would show some unnatural behaviour. That apart, these fishes are very social and they enjoy themselves with their tank mates.

Remember, keeping too many males together again leads to an uncomfortable environment within the tank. To sort this out, outnumber the females than males and this will keep the irritation of males at low.

Lifespan of Black Molly

The Black Molly fishes have an average life expectancy of almost 3 years while they live for 5 years in the wild. Though not generally found in the wild, the subspecies of the Molly fishes tend to live for 5 years on an average.

Diet of Black Molly

Black Molly fishes are omnivorous when it comes to their feeding habit. They would love it if the foods and diet are kept in the most natural manner. While we speak of meaty protein, you can provide them with different invertebrates. You can also give them live foods and frozen ones, which include Daphnia, Brine shrimp, Bloodworms and Blackworms. However, these fishes prefer a vegetable-based diet. In order to make sustenance, you must feed them with ample veggies. This includes,

  • Zucchini
  • Shelled peas
  • Cucumber

These vegetables must be included in their diet almost twice a week. In fact, they must be fed with flake food as it breaks up easily and can be digested easily. These flakes do not cloud the water. Moreover, these fishes prefer to have algae in their diet. Keep a layer of algae always in your tank, so that the Blackies can get a supply of natural algae whenever they want.

Tank Requirements for Black Molly

The tank must be very much appropriate for your fish to thrive in and the requirements must be fulfilled. Let us look into the relative parameters.

Tank Size

The minimum tank size for the Black Molly fish is 20 Gallons. This is because these fishes require minimum available space to roam around freely. The main reason behind providing them with a medium-sized tank is to avoid any kind of aggression. These fishes are to be kept in groups of 5-6 and hence, they need to avoid any unwanted irritation. However, strange to know that these are small critters but they would do their finest in a 45-gallon tank.

Tank Lid

It is basically not likely for a Black Molly to jump out of the tank. They are very calm and stay in their dwelling region. However, if disturbed they might show aggression and might jump out of water. Even if they are sick, they sometimes swim on the top level of the water. This is mainly caused by swim bladder disease. This would bring them to risk as floating on the top level would lead to accidents. This is best for them to be kept under a tank lid, which is sturdy and would not allow any foreign particles to get accumulated within the water,


Keeping the Black Molly fishes on a sand substrate is highly recommended. The whole body of the Mollies are soft and their black colour can best be reflected on light brown sand. Basically, they are not much affected by the substrates because they are middle-level dwellers.

Be it your Black molly or a common Yellow Molly, keep them in the aragonite sand substrate as this leach minerals from water. There is no hard and fast rule that you have to use sand. Using gravel substrates with an ample amount of corals (in crushed form) serves right as a proxy to aragonite.


Filtration of the water is very important as the Mollies cannot withstand any dirt or unhygienic substance within the water. You are free to use hang on back filters (this keeps the flow of water slow and also does not create any vibration in the water surface). However, the best will always be a canister filter. Using these kinds of Power filters will keep the tank sparkling.


The male fishes try to nag the females as they always like to mate. This crucial situation makes the female fishes tired. In fact, if kept with any larger fish, they need a place to hide. There must be rocks, hideout places and caves within the tank. The fishes like to swim through some hollow places, for which you can put figurines through which they can swim and enjoy. Keep your fish stress free with help of proper decorations.

Presence of Flora

A Black Molly tank must be always kept full of plants so that they get space to hide. They actually appreciate the planted environment where they are happy with their survival chances. The fries get a chance to hide and save themselves from their parents. There are a few plants that you can keep in the tank, which include

These plants, though do not help the adults much, however, the fishes feel very comfortable as they swim through the plants.


For these fishes, the aquarist can use any kind of light source. This might include sunlight or even any kind of artificial light. You need to keep the plants healthy and fresh, for which proper light source is important. In fact, the light would help algae to grow so that these fishes can have a natural food supply.

Cleaning Method

While cleaning the tank, you can use any soft cloth and rinse the walls clearly. In fact, you need to change the water in order to keep the ammonia and nitrates in check.

Water Types for Black Molly

The requirement for the water is very important as any kind of disbalance in the temperature or the other parameters might invite any kind of danger. Interestingly, the Black Molly is the cross-breeding result of Sailfin Molly and a common Molly and is completely aquarium bred. Hence, the water type required for thriving is freshwater, though they can survive in brackish water conditions even.


The required range of water temperature is generally from 21 to 26 Degrees Celsius. They prefer to thrive basically in tropical water.

pH Level

The perfect pH level to be maintained for the Black Molly fishes are 7.0-8.5. The fishes neither enjoy too much acidic water nor do they prefer any soft water type. Thus, it is important to scan the water range frequently.


Maintain the hardness level from 20.0 to 35.0 dGH.


The fishes cannot stand too much ammonia and nitrates. It is always advisable to monitor the range and remove the excess amount.

Compatibility of Black Molly

The Black Molly fishes are generally tranquil in nature and they can easily stay with any other fish that are not disturbing and aggressive towards them. You can keep them with other livebearers and always remember to keep a few plants within the tank so that the little babies hide from any danger.

Suitable Tank Mates

The suitable tank mates for these Mollies are

  • Guppies
  • Danios
  • Tetras
  • Endlers Livebearers
  • Angelfish
  • Swordtail
  • Platy Fish
  • Gouramis
  • Other Molly fishes

Apart from these fishes, you can also keep Snails  (only full-grown adults) with the Black Mollies.

Unsuitable Tank Mates

Try to avoid keeping any kind of long and flowy-finned fish with these Mollies. They are fin nippers and they continuously prick other fishes’ fins. In fact, you must not keep two male Mollies together as male fishes try to establish dominance and territorial instinct by nipping other males. Avoid keeping the few below-mentioned fishes

  • Bettas
  • Barbs
  • Goldfish
  • Shrimps (they eat away baby shrimps tearing apart their shell)

Breeding of Black Molly

Breeding the livebearers is the easiest of things, and your Black Mollies would not keep you unsatisfied. The females are always kept in large numbers than the males where the ratio is generally, 1:4 (one male for four females). The females are bigger in size and the males have distinctive gonopodium, which helps them to mate easily. Basically, the hooked shaped anal fin helps the female fish to get attached to the male and serve the best at the moment of depositing the sperm. It is completely upon you to separate the females or keep both parents together. To avoid chances of miscarriage, it is better to not shift the impregnated ones during the last stage of pregnancy.


To know if a Black Molly is pregnant, watch out for a gravid spot in the anal fin. If not, you can see the plumpy belly.

The seducing dance helps the females to get attracted whereas the males try to mate with even unaware females.

The ratio mentioned above is the best way to monitor the breeding procedure as one female cannot handle one male at a time. During breeding, the males become aggressive and they can keep calm only a few more females tackle them altogether. Keeping the Molly fishes together under a proper tank setup will surely present you a fries within some months. If the parents are healthy, you can certainly see at least 50-100 fry during every birth process and the whole process from being pregnant to giving birth takes a time of 4 weeks.

There is no need for special treatment, care and diet for the babies, however, you can give them good flakes, brine shrimps, microworms and daphnia.


Keep your Molly babies in the hiding regions or separate the parents as they do not show any parental instinct and might feast on the fries.

Diseases and Treatment of Black Molly

These fishes are very hardy and they get a compromised immunity. They get the most common diseases that most freshwater fishes are affected by. The Molly disease, fin rot and dropsy are namely recognised in the Black Molly fish. Molly disease is common in many viviparous fishes that occur owing to the bad condition of the water. As a symptom, you would see that a victim is less active and just swims in one place.

As we speak of fin rot, we find that this disease is a result of fin nipping by larger fishes or even owing to stress. The Black Mollies also face infection of dropsy (mainly infects those with lower immunity). Due to this disease. There is a huge amount of fluid that gets stored in the fish’s stomach and gradual spreading causes untimely death.

With all these diseases known to you, you will certainly try to know the possible remedies for those. In order to keep your other fishes safe, it is better to quarantine the affected one and then keep the treatment going. For treating Molly’s disease, regulate the water parameters and feed them well. While you put anti-fungal treatments to a fin rot disease, do not stop the proper antibiotics. Finally, for Dropsy, keep changing the tank water and find your fish healthy within a few days.


To conclude, the Black Molly fishes can adapt to any water condition and you can keep them with any kind of fishes. This gives you the chance to pet different colourful fishes with distinct black-coloured Mollies. We strongly recommend beginners to keep these Black beauties so that your journey to become a veteran becomes easy.

Interesting Fact: The males generally fertilize the eggs when they are within the female body. This makes them known as viviparous. The whole spermatophores are poured into the female and then instantly the eggs are fertilized. Interestingly the extra amount of sperm is stored in the oviduct so that it can be used at a later stage.

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