Shortfin molly

Poecilia mexicana

Also known as Atlantic molly

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: Easy
Rarity: Common
Origin: Mexico, Guatemala
Family: Poeciliidae

Overview

Keep them in groups with more females than males to spread out male attention, and plan on a tank of at least 120 liters since they get bigger than most mollies. They cruise the middle of the tank and stay peaceful with similar community fish. Feed an algae-heavy diet of spirulina flakes, blanched veg, and the occasional frozen food. They want hard, alkaline water and warm temperatures.

In the wild

Shortfin mollies range from Mexico down through Guatemala, living in warm coastal streams, springs, and brackish edges. They handle a wide range of conditions, including some salt. Give them a planted tank with hard, alkaline water (pH 7 to 8.5) and a temperature in the mid-20s C. A bit of marine salt is optional and not required for freshwater keeping.

Good to know

This is Poecilia mexicana, a livebearer in the family Poeciliidae. Adults reach about 11 cm, with females larger than males. Females give birth to free-swimming young rather than laying eggs, and a single mating can fertilize several broods. Expect a lifespan of roughly 3 to 5 years.

Did you know

In the wild, Poecilia mexicana includes populations living in sulfur-rich cave springs, where the water carries toxic hydrogen sulfide and very little oxygen. Those fish have evolved special tolerance to survive conditions that would kill most other species.