Black Molly

Fish that are completely black all over their bodies are extremely rare in nature. As a cultivated form, however, they occur in some fish species. The Black Molly stands out in particular, as its blackness surpasses any other fish.


  • Name Black Molly, Poecilia spec.
  • Systematics: Live-bearing tooth carps
  • Size: 6-7 cm
  • Origin: USA and Mexico, hybrids from different Poecilia species
  • Attitude: easy
  • Aquarium size: from 54 liters (60 cm)
  • pH value: 7-8
  • Water temperature: 24-30 ° C

Interesting Facts About the Black Molly

Scientific name

Poecilia spec.

Other names

Poecilia sphenops, Poecilia mexicana, Poecilia latipinna, Poecilia velifera (these are the original species), midnight molly, black double sword molly


  • Class: Actinopterygii (ray fins)
  • Order: Cyprinodontiformes (Toothpies)
  • Family: Poeciliidae (tooth carp)
  • Subfamily: Poeciliinae (viviparous toothcarps)
  • Genus: Poecilia
  • Species: Poecilia spec. (Black Molly)


The Black Molly, which corresponds to the type of the black muzzle (Poecilia sphenops) (photo), reaches a length of 6 cm (males) or 7 cm (females). Black Mollys, which are descended from the marigold (Poecilia latipinna), can grow up to 10 cm.


The body of the “real” Black Molly is black throughout, including the caudal fin, abdomen and eyes. In recent years, however, crosses with the gold or gold dust molly have come onto the market, which have a yellowish caudal fin, some shiny scales, a light belly and a lighter eye. Black Mollys from the Sailing Parrot can have a red border on the huge dorsal fin and are then called midnight mollys.


In the wild, black-spotted specimens of the actually olive-colored marigolds occur in the USA and Mexico. In the 1930s, it was first possible in the USA to produce purely black fish from it. By crossing it with the small-finned black-muzzle, the Black Mollys, which are just as short-finned, were created (photo).

Gender differences

Like all males of the viviparous tooth carps, the male of the Black Mollys also has an anal fin, the gonopodium, which has been transformed into a reproductive organ. The females have a normal anal fin and are also significantly fuller than the slender males.


Black Mollys are viviparous. The males fertilize the females after an elaborate courtship with the help of their gonopodium, the eggs are fertilized in the female and also mature there. About every four weeks – the females are then almost misshapen – up to 50 fully trained young are born, which are a tiny likeness of their parents. Since the adults practically do not chase after their young, they always get through enough when there are no predators.

Life expectancy

Black Mollys of the small-finned variant can live 3 to 4 years old, while the large-finned fish, which are descended from the common parsons, can live for five to six years.

Interesting Facts


In nature, mollys feed mainly on algae. In the aquarium, you can see the Black Mollys again and again at the plant leaves (without damaging them) or plucking furniture around in search of algae. Plant-based dry food is an excellent food for young and old.

Group size

Extremely peaceful towards other fish, the males can be very contentious among themselves. In a small aquarium, you should therefore only keep one male with three to five females. In this group, called “harem”, the original forms also occur in nature. If you want to keep a larger group, there should be at least five males and ten females (assuming a sufficiently large aquarium).

Aquarium size

An aquarium from 60 l is sufficient for a group of the small-finned Black Mollys. If you want to keep several males, you have to add at least 30 liters per male. The Black Mollys, which are descended from the marigold fish, need very large aquariums from around 400 l in order to be able to develop their large fins properly.

Pool equipment

A gravelly ground with a few stones and plants, which offer young fish and females who want to withdraw from the stalking of the males, some protection, is ideal. Wood is annoying because its tannin content can acidify the water, which is not well tolerated.

Socialize Black Mollys

All fish that are not too big (then the Black Mollys become shy) can be kept with the Black Mollys. If you attach importance to having plenty of offspring, no fish such as larger tetra or cichlids may be kept with the Mollys.

Required water values

The temperature should be between 24 and 30 ° C, the pH value between 7.0 and 8.0. The Black Molly needs a little more warmth than its olive-colored relatives and trunk forms.

Mary Allen

Written by Mary Allen

Hello, I'm Mary! I've cared for many pet species including dogs, cats, guinea pigs, fish, and bearded dragons. I also have ten pets of my own currently. I've written many topics in this space including how-tos, informational articles, care guides, breed guides, and more.

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