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Molly

Poecilia sphenops

Freshwater Central America Usually captive bred

A livebearer that does better in harder, alkaline water. Many are sold as black mollies. Males harass females, so aim for more females than males. It nibbles algae and soft plants.

Also called: Black mollie, Black Molly, Liberty mollie, Mexican molly.

7.5 cm adult length, drawn to scale. deep body.

Try it in the planner Opens a tank sized to its minimum with 1 fish added.

What it needs

ItemValueBecause
Adult length 7.5 cm Used for the Space check: the tank must be long enough for the fish to turn round.
Smallest tank 90 L, at least 80 cm long estimated The least water and floor length this species is kept in for good, as a single fish or smallest group.
Extra water per added fish 10 L estimated What each further fish adds once the minimum is met.
Waste load Class 3 of 5 estimated How much waste an adult makes against its size. Feeds the Load check.
Temperature 24 to 28 C Stock sharing a tank need overlapping ranges.
pH 7.2 to 8.5 Compared with tankmates in the Water check.
Hardness GH 12 to 25, KH 8 to 18 Degrees of general and carbonate hardness.
Flow Medium Low-flow fish are stressed in a strong current.
Light Moderate Matched to the lighting class on the needs sheet.
Group size Single fish is fine Not a schooling species.
Temperament Peaceful Not territorial.
Swims in Middle water Fish that use different levels share a tank more easily.
Lifespan About 4 years A fish is a long commitment.
Experience Suits a first tank A guide to how forgiving the species is of mistakes.
Jumps Yes Keep the tank covered.

Tags marked estimated are judged from the size and habits of the species rather than measured, so treat them as a sensible default.

Diet and tank layout

Molly is an omnivore that swims in the middle of the tank. It leaves most plants alone. Give it some cover.

Tankmates

Works with

Depends

Avoid

Compare any two fish on the compatibility page, or print the equipment for a stock on the needs sheet. How this is worked out: the method.