TankBud

Shortfin molly

Poecilia mexicana

Also known as Atlantic molly, Poecilia mexicanus

FreshwaterBrackishFish

Shortfin molly (Poecilia mexicana)
Dnoerholm · CC BY-SA 4.0

Care at a glance

Temperature
72–82°F
22–28°C
pH
7.0–8.5
Adult size
4.3 in
11 cm
Minimum tank
32 gal
120 L
Temperament
Peaceful
Social behavior
Social
Swim level
Middle
Difficulty
Easy
Breeding
Livebearer · Easy
Rarity
Common
Family
Poeciliidae
Origin
Mexico, Guatemala

Overview

The shortfin molly is a peaceful livebearer for the middle of a hard-water community tank. It is easy to keep.

Did you know

Some wild shortfin molly populations live in sulfur-rich cave springs. The water there carries toxic hydrogen sulfide and very little oxygen. Those fish have evolved a special tolerance that lets them survive conditions that would kill most other species.

Caring for the shortfin molly

Keep shortfin mollies in a group with more females than males, which spreads out the males' attention. They get bigger than most mollies, so plan on a tank of at least 32 gal (120 L). A planted tank suits them, and they cruise the middle of the tank.

Give them warm, hard, alkaline water at 72 to 82°F (22 to 28°C) and a pH of 7.0 to 8.5. They handle a wide range of conditions, including some salt. A bit of marine salt is optional and not required for freshwater keeping.

Feed an algae-heavy diet of spirulina flakes, blanched vegetables and the occasional frozen food. Shortfin mollies stay peaceful with similar community fish.

Females grow larger than males. A female gives birth to free-swimming young rather than laying eggs, and a single mating can fertilize several broods. Breeding shortfin mollies is easy.

Good to know

The shortfin molly, Poecilia mexicana, is a member of the family Poeciliidae. It lives roughly 3 to 5 years.

In the wild

Shortfin mollies range from Mexico down through Guatemala. They live in warm coastal streams, springs and brackish edges.

Weekly picks

Tank mates

The shortfin molly is a peaceful, social species that keeps to the middle. These picks share a community profile with it, are safe together in both directions, and overlap on water type, temperature and pH.

Check the full mix in the stocking calculator

Common questions

What size tank does a shortfin molly need?

A shortfin molly needs at least 32 gal (120 L). It spends most of its time in the middle.

What temperature and pH does a shortfin molly need?

A shortfin molly is comfortable at 72–82°F (22–28°C) with a pH of 7.0–8.5.

What does a shortfin molly eat?

A shortfin molly eats an algae-heavy diet of spirulina flakes and blanched vegetables. Give it the occasional frozen food as well.

How big does a shortfin molly get?

An adult shortfin molly reaches about 4.3 in (11 cm).

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

Males stay smaller than females, which grow larger.

How does a shortfin molly breed?

A shortfin molly female gives birth to free-swimming young rather than laying eggs. A single mating can fertilize several broods, and breeding them is easy.

Related species