TankBud

One species · 4 varieties

Black molly

Poecilia sphenops

FreshwaterBrackishFish

Black molly (Poecilia sphenops)
The Wet Spot Tropical Fish · Used with permission

Care at a glance

Temperature
70–82°F
21–28°C
pH
7.0–8.0
Adult size
4.7 in
12 cm
Minimum tank
24 gal
90 L
Temperament
Mostly peaceful
Social behavior
Social
Swim level
Middle
Diet
Omnivore
Difficulty
Easy
Breeding
Livebearer · Easy
Rarity
Very common
Family
Poeciliidae
Origin
Venezuela, Colombia, Mexico

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One setup covers every line on this page: care is the species' care.

Overview

The black molly is a social livebearer that swims in the middle of a community tank. It is easy to keep and a good first fish for hard, alkaline water.

Did you know

Black mollies are prone to a swimming quirk called the shimmies, where the fish wiggles in place without going anywhere. It is not a disease but a stress signal, usually from water that is too soft, too cool or has gone off. It often clears up once conditions improve.

Caring for the black molly

Keep black mollies in a small group in a tank of at least 24 gal (90 L). A planted tank with open swimming space and steady warmth suits them. They spend most of their time in the middle of the tank.

Give them hard, alkaline water at 70 to 82°F (21 to 28°C) and a pH of 7.0 to 8.0. They tolerate, and often appreciate, a little salt in the water.

Black mollies graze algae and need real plant matter in their diet. Feed a vegetable-based flake or pellet with some protein mixed in.

They are mostly peaceful and safe with other community fish. Keep more females than males to spread out the males' constant chasing. Females grow larger and rounder than males. Males carry a gonopodium, a modified anal fin used to fertilize females.

Black mollies are livebearers and give birth to free-swimming young instead of laying eggs. They breed easily, so expect fry.

Good to know

The black molly is a melanistic, captive-bred color form of Poecilia sphenops. It belongs to Poeciliidae, the livebearer family, and the all-black fish is an aquarium strain.

In the wild

Black mollies trace back to coastal fresh and brackish waters in Mexico, Colombia and Venezuela, including streams and estuaries near the sea.

Weekly picks

Tank mates

Every variety on this page wants the same water, so one set of picks fits them all. These picks match on water type, temperature, pH, size and temperament.

Check the full mix in the stocking calculator

Common questions

What size tank does a black molly need?

A black molly needs at least 24 gal (90 L). It spends most of its time in the middle.

What temperature and pH does a black molly need?

A black molly is comfortable at 70–82°F (21–28°C) with a pH of 7.0–8.0.

What does a black molly eat?

A black molly grazes algae and needs real plant matter. Feed it a vegetable-based flake or pellet with some protein mixed in.

How big does a black molly get?

An adult black molly reaches about 4.7 in (12 cm).

How can you tell a male black molly from a female?

Males carry a gonopodium, a modified anal fin they use to fertilize females. Females grow larger and rounder than males.

How does a black molly breed?

A black molly is a livebearer, so it gives birth to free-swimming young rather than laying eggs. It breeds easily, and you can expect fry.

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