Fish Profile: Black Molly 3

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Black Molly

The Short-Finned Molly (Poecilia sphenops), also known as the Black Molly or Common Molly, is a very popular aquarium fish native to Mexico.

Their hardiness and wide range of colors makes these fish a good choice for beginners.

There are many different varieties of the Short-Finned Molly, including Dalmatian, Lyre-tail harlequin, platinum, gold dust and black.

They are very closely related to the Sailfin Molly (Poecilia latipinna) and the Giant Sailfin Molly (Poecilia velifera), hybrids of those species also exist.

Even though Mollies are usually thought of as freshwater fish they have a unique ability to thrive in fresh, brackish or salt water.

Black Molly – General Care

The Short-Finned Molly needs a tank of least 30 gallons with plenty of tough plants such as Java Fern, Sagittaria, Vallisneria, or Anubias. Mollies have a taste for plants and will destroy softer-leaved plants.

Good filtration is recommended as this fish should be kept in water with zero ammonia and zero nitrite.

Mollies require hard, alkaline water with a pH between 7.5 -8.2 and it is adapted to live in a wide range of water temperatures, anywhere between 70-82 0 F will do. The addition of one teaspoon of aquarium salt per gallon will help this thrive.

With proper care and enough space the Short-Finned Molly should live around 2-3 years.


In captivity this fish is not difficult to feed and it readily accepts flake and pellet foods.

Ideally a good portion of their diet should consist of vegetable matter in the form of spriullina flakes or blanched vegetables such as spinach, zucchini or peas.

Their diet can also be supplemented with frozen bloodworms or brine shrimp which are excellent colour enhancers.


The Short-Finned Molly is sensitive to stress and should not be kept in aquariums with overly large or aggressive fish.

They are a good choice for hard-water community tanks and do well with some species of danio, barb or rainbow fish.

Although they are not a schooling species they are social and should be kept in groups of at least three.

If you plan to keep groups consisting of males and females it is wise to have a 3:1 ratio of females to males.


Males can be distinguished from females by the gonopodium which looks like a pointed extension on the anal fin and is fairly easy to see on adult fish.

Generally no special steps need to be taken for breeding to occur, all that is needed is good water male and female fish and they should breed.

Even if you only have female fish you may find that they are having babies, this is because females have the ability to store the male’s sperm for several months which allows them to reproduce long after they have been separated from the male fish.

Every 60-70 days the female will give birth to 10-60 young that are already approximately one-half inch long and free swimming.

If you want to raise the young to adulthood the presence of floating plants such as hornwort can help the young survive by giving them a place to hide.

If they have nowhere to hide they will likely be eaten by the larger fish in the tank. They can also be transferred to a separate grow-out tank to be raised to adulthood.

The young fish can be fed small pieces of flake food or newly hatched brine shrimp.


The Short-Finned Molly is a hardy fish, especially when kept in hard water with a small amount of salt added, however when stressed or kept in less than ideal conditions it can become susceptible to disease.

Temperature fluctuations, especially cooler temperatures leave the Short-Finned Molly prone to disease. Ick and Velvet disease are the most common diseases in this fish.

Fact Sheet – Black Molly

  1. Scientific Name: Poecilia sphenops
  2. Family: Poeciliidae
  3. Order: Cyprinodontiformes
  4. Class: Actinopterygii
  5. Size Range: between 7.5- 12.5 cm in length, females are larger than males
  6. Diet: Omnivore
  7. Tank Size: 30+ gallons
  8. Tank Set-up: Moderately planted
  9. Tank region: Top and middle
  10. Temperature: 70-82° F
  11. Carbonate Alkalinity (dKH): 10-25
  12. Water pH: 7.5-8.2
  13. Origin: Mexico
  14. Temperament: Peaceful
  15. Lifespan: Up to three years
  16. Lifespan: 2-3 years
  17. Reproduction: Livebearers
  18. Reproduction: Breeds easily in captivity

Picture Gallery


Other Helpful Resources

  1. Fishbase – Poecilia sphenops
  2. Wikipedia – Peocilia sphenops wiki
  3. Live Aquaria – Block Molly
  4. Fish and Tips – Poecilia sphenops (Black Molly)

Share Your Thoughts

Have you kept the Short Finned Molly in your aquarium before? Please share your experience with us and any tips for their care in the comments section below.

About Dennis Hanson

Dennis is an experienced aquarist with many years of knowledge and experience in keeping successful tanks. He also has no relations to the pop group Hanson.

3 thoughts on “Fish Profile: Black Molly

  1. Pingback: 10 Best Freshwater Aquarium Fish For Beginners | Home Aquaria

  2. Reply Shelly M. Mar 11,2014 6:12 pm

    I bought some live plants and before i knew it i had baby snails. Did the plants already have the small snails on them? Shelly m.

  3. Reply Gavin B. Nov 29,2017 5:18 pm

    I’m a Jr. in high school and I’m taking Aquatic Science. Next Semester (January 7, 2018) We’ll be starting tank care and need to have our fish picked out by then. I like the look of Mollies and The Black Molly seriously caught my eye due to the size and easy care. We are in groups of 4 & given a 20 Gallon tank for each group and we all need to have a fish. This page has helped me tremendously already but I have a few questions:

    1. When it says they do better in planted tanks, does it matter if we use plastic plants? We’re in that class for 50 minutes at a time and I’m not confident that we can maintain the plants properly along with the 4 fish.

    2. Do they need tank-mates of the same species or can I keep it in a tank with different fish? We only get 1 fish each and they can’t be the same species.

    3. I read that they’re aggressive breeders, will he/she get depressed, just float around, stop eating, etc…?

    4. What kind of “hiding places” should I buy? Are plastic/ceramic pirate ship, castle, pineapple, things like that, bad for it or not be interested and I’ll have wasted some money.

    I plan on keeping him/her after the 5 months we take care of them at the school and I just want to make sure I’m not messing up.

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