Why is my Molly shaking back and forth in one spot?

This behaviour is known as 'the shimmies' and is typically a sign of severe osmotic stress. It occurs when a Molly is kept in water that is too soft or acidic. Raising the general hardness (GH) and ensuring the pH is alkaline will usually cure it.

Do Sailfin Mollies absolutely need salt in their water?

They do not strictly require salt if your tap water is naturally very hard and alkaline. However, they are a coastal species, and adding a small amount of marine salt (creating a lightly brackish environment) greatly improves their immune system and overall health.

How can I tell a male Sailfin Molly from a female?

Males are easily identifiable by their enormous, sail-like dorsal fin and a modified anal fin called a gonopodium, which resembles a small stick. Females are larger, plumper, have a standard rounded anal fin, and possess a much smaller dorsal fin.

Why did my female Molly have babies when she is alone in the tank?

Female livebearers can store sperm for up to six months after mating. If she was in a tank with males at the shop before you purchased her, she can produce several batches of fry without mating again.

Can I keep Sailfin Mollies with Neon Tetras?

It is not recommended. Neon Tetras require soft, acidic water to thrive, while Sailfin Mollies need hard, alkaline conditions. One of the species will suffer if kept in a compromise environment.

FreshwaterTropicalBeginner

Sailfin Molly

Poecilia latipinna

A vibrant, hard-water loving livebearer famous for the male's spectacular, sail-like dorsal fin.

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Ideal Conditions

Temperature: 21 – 28 °C
pH range: 7.5 – 8.5
Hardness: 15 – 30 dGH
Salinity: 1 – 1.015 SG
Adult size: 10 – 12 cm
Standard adult setup: 120 litres+
Lifespan: 3 – 5 years
Diet: Omnivore (Herbivore leaning)
Water flow: moderate

About the Sailfin Molly

The Sailfin Molly is a robust and lively centrepiece for hard-water or brackish aquariums. Renowned for the male's extraordinary dorsal fin, which is flared in elaborate courtship displays, this species has been a staple in the aquarium hobby for decades. While wild-type fish display beautiful subtle silver and green hues with pearlescent spotting, selective breeding has yielded an enormous array of colour forms. They are highly active, entirely peaceful towards other species, and bring constant movement to the upper levels of the tank.

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Where Sailfin Molly comes from

Native range

North America, Central America

Countries / regions

United States, Mexico

Habitat

Coastal waterways, estuaries, swamps, ditches, and lowland streams

Highly adaptable euryhaline species, found from entirely fresh water to hypersaline coastal environments.

Similar species

Yucatan Sailfin Molly
Poecilia velifera
Shortfin Molly
Poecilia sphenops
Liberty Molly
Poecilia gillii

We’re adding more full species guides as the catalogue grows.

Compatible tank mates

Reviewed guidance based on this species' recorded traits.

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Swordtails
Xiphophorus hellerii
Share the requirement for hard, alkaline water and have a similar activity level without direct competition.
Great
Guppy
Poecilia reticulata
Another poeciliid that thrives in hard water and peaceful community settings.
Great
Bumblebee Goby
Brachygobius spp.
An excellent bottom-dwelling companion if keeping the mollies in a brackish water setup.
Great
Neon Tetra
Paracheirodon innesi
Prefers soft, acidic water, which conflicts directly with the molly's need for hard, alkaline conditions.
Compatible with caution
Tiger Barb
Puntigrus tetrazona
Notorious fin-nippers that will shred the male molly's spectacular dorsal fin.
Not recommended

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