One of the most common freshwater fish in the aquarium hobby today, and quite often the most unusual, is the Black Molly.
Unlike the other types of Molly fish available in the fish keeping hobby, the Black Molly gets the majority of its traits as a result of captive breeding and you would struggle to find one in the wild.
It’s pretty obvious where the Black Molly gets its name from, but what isn’t as obvious is how they came to obtain such a dark, distinct color.
Almost all Black Mollies will be born with a serious case of melanism, which is a skin condition opposite to albinism (the lack of color pigmentation).
While the majority of Black Molly fish are completely black, they can sometimes be found with a streak of yellow which runs down the dorsal fin, or a slightly silvery color on the flanks.
Black Mollies are relatively small in size, with the males growing to a maximum of 3 inches, and the females often growing a couple of inches larger.
Their lifespan will completely depend on how well they are cared for, but in the perfect scenario, Black Molly fish can live up to 5 years in captivity.
Perfect Tank Conditions For Black Molly Fish
The first thing to take into consideration when setting up your tank to house Black Mollies is the ratio of the two sexes.
Black Mollies are generally a peaceful community fish, but multiple males kept in the same tank can become aggressive, and females which are outnumbered by males will tend to be harassed.
The optimal ratio that we recommend is 3 females to each male. Male Mollies are aggressive breeders, so providing more females will help divide the attention between them, to prevent any one female from receiving constant attention.
Failing to stick to this ratio, or one thereabouts, you may find that your females will become too stressed to eat and could potentially die.
It is often thought that Black Mollies are best served in Brackish waters, but that’s not the case at all. While it’s true that they can survive in almost any water conditions, they will be better off kept in freshwater tanks.
Mollies love space to move and since you should be keeping them in larger groups to prevent any unnecessary harassment or aggression, you will need a tank that is big enough to accommodate them.
The best tank size for a Black Molly is at least 20 gallons but if possible, a 45-gallon tank would be much better.
In terms of pH and temperature, we would recommend that you keep your Black Mollies in water that is between 70 and 80 degrees Fahrenheit, with a pH that is closer to the harder, more alkaline side of the spectrum (7.5 – 8.2).
Mollies are very sensitive to changes in water parameters, so it’s important that you keep the tank environment as consistent as possible.
Black Mollies love planted aquariums, so the more plants you have, the better. The plants will not only allow the adult fish to feel more comfortable, but they will also increase the survival rate of the fry.
Mollies are notorious when it comes to feeding on their fry, so giving them a place to hide will help your breeding efforts enormously. Pretty much any plants will do the trick, but here are a few of the ones we would recommend:
- Java Ferns
- Amazon Sword
- Java Moss
Filtration For Black Molly Tanks
Most filters will work well when keeping Black Mollies so it completely depends on what you currently have access to or what you can afford. While a lot of other fish keepers will recommend a canister filter, we believe they are a little bit too expensive when it comes to keeping Mollies.
A simple hang on the back filter is cheaper and will not disrupt the water surface as much as most other filter types. Mollies love to swim on the surface looking for floating food so we recommend choosing a filter that leaves the surface as smooth as possible.
What Do Black Mollies Eat?
Feeding Black Mollies is pretty simple since they will happily eat a wide variety of different foods that you probably already have lying around.
First of all, Black Mollies are algae eaters, so if your tank is prone to green algae breakouts, your Black Mollies will help control it from getting any worse.
Mollies are omnivorous fish so in order to keep their diet as natural as possible, we recommend feeding them a variety of invertebrates as well as plant matter and some detritus.
Being omnivores, Mollies do require a small number of vegetables in their diet in order to survive. They will eat just about any green vegetable but we recommend sticking with zucchini, cucumbers, and shelled peas. You should strive to feed them vegetables at least once per week but twice if you can.
The base of a Black Molly’s diet should be a high-quality flake food, such as the TetraMin Flake by Tetra. We get ours from Chewy.com, it’s less than $5 a tub and it’s the best flake food I’ve ever used. It breaks up easily and doesn’t disintegrate and cloud your water like a lot of cheap flakes do.
You should supplement the flake foods with live or frozen foods such as bloodworms, blackworms, daphnia and brine shrimp. (Mine can’t get enough of this brine shrimp).
As with most fish, the Black Mollies prefer their foods live but we know how difficult it can be to find them sometimes so frozen is definitely the next best thing.
How To Sex Black Molly Fish
As with most other livebearers, sexing a black molly fish couldn’t be any easier.
Females will always be larger than the males, and the males can be distinguished thanks to their gonopodium, which is an anal fin that is shaped similar to a hook and serves the purpose of hooking onto the female molly fish when ready to deposit sperm.
How To Breed Black Molly Fish
If you follow the general advice of a three female to one male ratio, the breeding will generally take care of itself. Male Mollies are incredibly aggressive in their breeding habits so as long as the tank is set up in a way that the Mollies feel comfortable, you can expect some molly fry within a couple of months.
Some people keep the males and females together after impregnation and some will move the females to a separate tank. We have no preference so it’s completely up to you.
However, if you are thinking about moving the female to a separate tank, we recommend waiting at least a week before you do so to reduce the chance of a miscarriage caused by the stress of moving.
As we have already mentioned, the Black Molly fry will require plenty of plants to hide between if you want them to survive. Mollies are not the most considerate parents in the aquarium so they will eat any fry that they feast their eyes on.
You can tell if the female Molly is pregnant by looking at their anal fin, which should show a dark gravid spot. If that fails, the obvious increase in plumpness should be a solid indicator that she is carrying some fry.
The number of fry you can expect will depend on the age of the parent but on average, you will see anywhere from 40 to 100 fry per birthing. The entire process from impregnation to birth will usually take between 6 to 8 weeks but we have had cases where the gestation takes just 4 weeks.
The baby fry don’t require any special treatment after birth and their diets are the same as their parents from the get-go. A good quality flake such as TetraMin which has been ground up, as well as some small brine shrimp, daphnia or microworms will definitely do the trick.
To ensure the full development, we recommend feeding your newly born fry at least 3 to 4 times per day.
Black Molly Suitable Tank Mates
Black Molly fish are a peaceful, community fish who will happily live with almost any other peaceful, community fish. Some of the fish we have successfully kept with our Black Mollies are Guppies, Danios, Tetras, other Mollies, Swordtails, Gouramis, Platies and even female betta fish.
Black Mollies will generally live harmoniously with other livebearers but as we previously mentioned, livebearers have a reputation for eating their offspring so if you are interested in breeding livebearers in a community tank, make sure there are plenty of plants for the fry to hide.
4 thoughts on “Black Molly Care Guide (Diet, Tank & Breeding)”
This helped me a lot because I have a breeding Black Molly and the guy at the pet store told me that they give birth every 4 weeks and now I know that they give birth every 6 – 8 weeks
How many mollies can you keep in a 20 gal?
Once we realized our female black molly was pregnant we moved her to a breding time alone. We only had two and I’m still not good at ciphering between male and female but I realized that one was much bigger and concluded she was pregnant. Today there’s about 100 little black mollies swimming around in the time not sure if I should remove her and how soon should I remove her from the tank so she won’t eat any of the babies?
it does not tell me if black mollies give birth to live fry.