Black Molly: Care Guide, Diet, Tank & Breeding And More …

Black Molly

The deep black ornamental fish with a velvety sheen is extremely popular with both experienced aquarists and beginners. Thanks to its peaceful and robust nature, the pretty Black Molly is an asset to any aquarium. Those who love warmth react to temperature fluctuations; however, freshwater fish are sensitive.


Fish that are completely black from head to tail are rarely found in the wild. The Black Molly is not a “natural species” either, but a cultivated form of the black-muzzle, which actually shimmers silvery-green in its wild form. The “Wild Molly” belongs to the viviparous tooth carps and lives in slowly flowing freshwater waters in Central America as far as Colombia and Venezuela. The pure blackfish of Molly, known since 1909, was first successfully bred in the USA in the 1930s, from where they were exported to Europe and other parts of the world. Today they are among the most popular ornamental fish for freshwater aquariums, and, thanks to their elegant black scale dress and their peaceful nature, they have become an indispensable part of community tanks.


The first cultivated forms of the Black Molly imported from the USA were relatively small with a length of 4-6 cm and had a short, flat, and slightly angular dorsal fin. As a result of numerous crossings, among other things with sailfish, many more Molly variants have emerged over the years, which differ considerably in color, size, fin shape, and body proportions.

Male or female?

The best-known form of the Black Molly is undoubtedly the completely black variant with a pointed head and a rather smallmouth. The popular ornamental fish grow to a size of 6 to 10 cm, depending on their lineage, with females being slightly larger and more rounded than their male counterparts. Males can also be recognized by the reshaped anal fin, the so-called gonopodium, as well as by the usually larger dorsal fin.

Other forms of Black Molly

In addition to the black Mollys described here, there are also silver, spotted, and Dalmatian-like Mollys. In the last few years, crossings with the gold or gold dust molly, which have a yellowish caudal fin and lighter eyes, have become popular. Somewhat rarer are the so-called midnight Mollys – Black Mollys, descended from the sailing penguin, with a red border on a very large dorsal fin.

Why is the Black Molly so popular?

Of course, the Black Molly’s popularity was due to its beautiful black shed dress and its peaceful nature, which makes it an uncomplicated resident in community aquariums. The ornamental fish, which is not a schooling fish in the true sense of the word, but should always live in a group, is extremely fond of swimming and provides a welcome change in any aquarium. Another plus point for aquarists was the plant-loving fish due to its reputation as a good algae eater. Again and again, the lively blackfish pluck with their small, pointed mouth at plants and furnishings.

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How does Black Mollys breed?

Black Mollys are extremely prolific. After an elaborate courtship, the males fertilize the females with the help of the gonopodium, the anal fin that has been transformed into a mating organ. Several times a year, the females give birth to 30 to 80 fully trained young fish after a gestation period of approx. Four weeks, during which the female becomes bulky and fat. The lively Mini-Black Mollys explore their surroundings immediately after birth and seek protection from predators in dense vegetation. Even the young Black Mollys are quite robust so that a large number of the born fish survive the critical first weeks. In contrast to other, more aggressive species, the older Black Mollys rarely chase after the young.

Keeping in the aquarium

Keeping Black Mollys is quite simple. The peace-loving blacks get along well with much other freshwater fish and with different living conditions and ways of feeding. However, keepers should make sure that these conditions are always the same because the dark ornamental fish are very sensitive to fluctuations of any kind, be it in relation to the water temperature, the acidity, or the pH value. Like many other well-bred forms of fish, they cannot tolerate water that is too hard or too soft, and an excessively high acid content also causes problems for the fish. Black Mollys prefer a water temperature of 26 to 28 degrees but can also cope with slightly cooler (at least 24 degrees) and slightly warmer aquarium landscapes (maximum 30 degrees) if necessary. Important is,

What does the ideal aquarium for Black Mollys look like?

Another reason why Black Mollys are so high on the list of the best-known ornamental fish is that they can be kept in smaller aquariums from an edge length of 60 cm, i.e., 54 liters. Of course, the following also applies to these fish that love to swim: the more space, the better. Gravel is recommended as the substrate. In addition, the aquarium should be greened with lots of fast-growing plants in order to offer the Mollys sufficient hiding places. The leaves of the plants should reach into the upper region of the aquarium since Black Mollys mainly move in the middle and upper regions of the aquarium. Even stones that are built up into small caves are popular with female Mollys as a retreat from intrusive males.

How many Black Mollys fit in an aquarium?

If the aquarium is set up as described above and the water temperature and quality are right, nothing stands in the way of Black Mollys moving into their new home. You should buy at least a group of five to six animals because even if Mollys are not schooling fish, they need conspecifics to feel comfortable. If you have a small aquarium with 54-60 liters, a composition of one male and four to five females is recommended. Several male rivals in too small a space could cause problems because Molly males are easily contentious with one another. In larger aquariums, several males can be kept, but the females should always form the majority. For each additional male, around 30 liters should be added to the total volume.

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The keeping recommendations for Black Mollys at a glance

Especially newcomers to the hobby aquarium hobby can quickly feel overwhelmed by the amount of information that can be found about Black Mollys. Don’t worry; Black Molly’s posture is easy if you keep a few points in mind. In the following, we will show an overview of the most important keeping requirements for Black Mollys:

  • Aquarium size: at least 54 liters (60 cm edge length)
  • Water temperature: 24 ° -28 ° C
  • pH value : 7-8
  • Total hardness: 11-30 ° dGH
  • Number of fish: in a small 60 cm aquarium, one male with four to five females. In larger tanks, the group may be larger (females always outnumbered)
  • Ground: gravel
  • Plants: Black Molly prefers dense and high plantings, so it is best to plant fast-growing plants. Hornwort and the easy-care Hygrophila are well suited.
  • Lining: Vegetable flake food. From time to time, mosquito larvae can be added.
  • Socialization: with many known freshwater fish species that place the same conditions on their surroundings and are also considered peaceful. Armored catfish, guppies, or platys, for example, are well suited.


What does Black Mollys eat?

The popular black ornamental fish are also considered to be easy to care for in terms of their diet, although they clearly prefer plant-based food. Since Mollys mainly take up their food on the water surface, light flake food with a pure or high proportion of plants should be used, which does not sink too quickly to the bottom. But now and then, they also like live or frozen food, such as mosquito larvae. Pure algae fish food can also be offered. It’s important that the fish are not overfed. Too much food not only harms the animals themselves but can also throw the entire ecosystem of the aquarium out of balance.

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How old do Black Mollys get?

If kept well, Black Mollys live to be three to five years old. As a result, the life expectancy is (as with most cultivated forms) below that of the wild black-mouthed fish, but compared to other, more disease-prone freshwater ornamental fish, it is in the upper range. The black ornamental fish are considered to be quite robust against diseases, but of course, Mollys are not entirely spared from diseases. The spot or white spot disease should be mentioned above all. As the name suggests, this so-called Ichthyo infestation can be recognized by small white dots on the fins or skin. If the disease is recognized in good time, it can be combated well by increasing the water temperature and adding salt. Does this not help

What to do if a fish falls ill

If a fish falls ill, you should not only treat the disease yourself but also identify and combat the causes. Reasons for a weakened immune system and thus a disease of the animals can, for example, bad pH values, incorrect water hardness, or water temperature that is too low. Black Mollys often show discomfort due to faulty conditions by rocking movements. If you notice this behavior, you should take action. When taking the necessary measures and treatments, you should always keep an eye on all the fish in your aquarium and your respective requirements. The addition of salt or an increase in temperature, for example, should also be tolerated by the other species.

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How often does the aquarium have to be cleaned?

Of course, you shouldn’t always wait for your fish to feel bad. Regular cleaning and checking of the water parameters help to keep the aquarium running. Change about 10 to 30 percent once a week and perform a larger water change of 30 to 50 percent every two to three weeks. Make sure that the freshwater has the same temperature as the existing one so that the fish are not exposed to temperature fluctuations. Regularly clean the filter and keep walls and furnishings clean. You should also test the water quality again and again with a test strip or a digital water tester, so you can be sure that the climate in your aquarium is right. Tall and fast-growing plants, like those the Black Mollys love, help keep the aquarium in a healthy balance.

Which ornamental fish does the Black Molly get along with?

Black Mollys are extremely peaceful fish that can be brought together and socialized with most species without hesitation. It is important that all fish that live together in an aquarium have the same requirements for water, light, temperature, and place plants. In addition, the fish species should populate as many different water regions as possible. In this context, bottom-dwelling catfish or fan shrimp are very suitable. But also with other freshwater fish like the well-known ones’ Platys, Guppies, Tetras, Scalars or even one siamese fighting fish usually have no problems. It could only be more difficult with larger, very lively fish such as cichlids because Black Mollys tend to get shy.

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