Gill's molly

Poecilia gillii

FreshwaterBrackishFish

Care at a glance

Temperature: 72–86°F (22–30°C)
pH: 7.0–8.5
Adult size: 3.9 in (10 cm)
Minimum tank: 26 gal (100 L)
Temperament: Peaceful
Social behavior: Social
Swim level: Middle
Difficulty: Easy
Breeding: Easy
Rarity: Very rare
Origin: Costa Rica, Panama
Family: Poeciliidae

Overview

Gill's molly is a sturdy, peaceful molly best kept in a group with more females than males. It swims mostly in the middle of the tank and gets along with other calm fish that share its taste for hard water. Like other mollies it grazes algae and aufwuchs all day, so base its diet on a vegetable-rich flake or pellet and add occasional frozen foods. It is happy in hard, alkaline fresh water and readily accepts a little marine salt, reflecting the brackish coastal creeks it lives in. Because it grows to a good size and stays active, give a group a tank of 100 liters or larger.

In the wild

Poecilia gillii is widespread on the Atlantic and Pacific slopes of Costa Rica and Panama, living in warm lowland streams, ditches and coastal lagoons from fresh into brackish water. It is used to hard, mineral-rich conditions, so keep a temperature between 22 and 30 C and a pH from about 7 to 8.5. A roomy tank with plants, open water and steady flow suits it, and a small amount of salt does no harm. Good light to grow algae gives it natural grazing.

Good to know

Gill's molly is a livebearer in the family Poeciliidae and reaches about 10 cm, making it one of the larger wild mollies. Males are slimmer and fertilize females internally with a gonopodium, the modified anal fin shared across the family, while females carry the embryos and give birth to live fry. It breeds easily in hard water and can produce large broods, so a group will steadily increase if the fry are given cover.

Did you know

Gill's molly is so adaptable that wild populations live everywhere from clear inland streams to salty coastal lagoons, and the same fish can move between fresh and brackish water without trouble.