Black Molly

Common Names: Black molly

Type Locality: N/A

Range: Not a natural species. Ancestral species range from the southern United States through Mexico and Central America

Taxonomic Troubles: Domesticated strains of mollies are of hybrid descent from a variety of natural species. Mollies are typically divided into long-finned species such as Poecilia latipinna and P. velifera, and short-finned species such as P. mexicana, P. sphenops, or P. fo

Size: 6 to 15 cm (3½ to 6 inches).

Preferred Water Chemistry: Hard, basic fresh water to brackish or marine. Mollies are euryhaline, meaning they do well in fresh, brackish, or marine systems, but they do not thrive in soft water.

Difficulty: A very hardy fish with one weakness: It requires mineral-rich, high-quality water. Mollies cannot tolerate any ammonia or nitrite.

Tank Setup: This fish needs room. A 20-gallon is the absolute smallest acceptable aquarium, and larger is much better. Filtration should be robust, and water changes must be frequent. Mollies are quite peaceful and will not bother tankmates too large to swallow. Avoi

Feeding: Primarily herbivorous. Will take any and all fish foods, but the diet should be largely based on algae and other plant material.

Breeding: Kept in high-quality water and given plenty of room, females will drop a brood of fry about once a month. Adults are not overly cannibalistic, and given some cover of floating plants, most of the fry should survive.

Fish Description

The black molly is completely black—body, fins, eyes. This is a flat, velvety black, without iridescence. Its unusual appearance has kept it a hobby favorite since the beginning. Black specimens exist in all types of mollies, from the smallest shortfins to the largest sailfins.


Mollies of all colors are often recommended for beginners, but they are also often considered delicate. That isn’t a coincidence. Because these fish require excellent, stable water conditions and plenty of room, they are actually bad choices for new hobbyists. Kept in an overcrowded, underfiltered 10-gallon tank, mollies will quickly fall ill. On the other hand, when kept in large tanks with quality water, especially with some salt, they do extremely well. Although they can and do thrive in pure fresh water, many aquarists believe that the largest, healthiest mollies are produced in brackish or marine setups.