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Encyclopedia / Livebearers / Molly
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Variations

11 kinds · tap one for a closer look

Molly

Poecilia sphenops · Black molly, Sailfin molly, Balloon molly, Dalmatian molly

Peaceful grazer needing hard water.

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8 cmBody length, without tail ✓
24–28 °CTemperature ✓
7.5–8.5pH ✓
81 LSmallest tank ✓
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Not recommended
  • White cloud mountain minnow needs cool water and makes a lot of waste, while Molly is tropical.
  • They need different temperatures (24–28 °C vs 14–22 °C). No setting suits both.
Not recommended
  • Giant gourami eats animals up to about 10 cm. Molly only grows to 8 cm.
Not recommended
  • They need different temperatures (24–28 °C vs 10–22 °C). No setting suits both.
With conditions
  • Only a narrow temperature range suits both: 24–25 °C.
  • Their pH needs don't quite meet (7.5–8.5 vs 5–7). Aim between the two and keep it steady.
With conditions
  • Their pH needs don't quite meet (7.5–8.5 vs 4.5–7). Aim between the two and keep it steady.
Compatible
Compatible
Compatible
Compatible
Compatible

145 species in our list are a good match.

Facts checked against sources on 16 Oct 2026. ✓ means a source backs it; ? means no reliable source yet. See sources

Care and water

Hardness ✓15–30 dGH
Group size ?3 or more
Temperament ✓Peaceful
Swims at ?Middle
Care level ✓Easy
Diet Omnivore
Lifespan ?Unknown
Size in shops 3–5 cm
Growth Fast

Behavior

Peaceful grazer needing hard water.

Food

Flakes plus plenty of vegetable matter.

Tap a food to see what it is.

Male or female

Male Molly
Male
Female Molly
Female

Males are smaller and more colourful and have a gonopodium; females are larger with a normal anal fin.

Health

Common problems. Tap one to see the signs. This is a guide, not a diagnosis.

Breeding

Livebearer · Easy

Livebearer; breeds readily, including hybridising with P. latipinna in aquaria.

Pairing

Keep 1 male with 2-3 females. Buy a group of 6 or more young fish and let them pair up on their own.

Setup

A 20 gallon (75 L) tank with plenty of plants or spawning mops. Add a pinch of aquarium salt and keep the water hard and slightly alkaline.

What starts it

Warm, clean, hard water and good food. Males chase females all year.

Eggs

20-150 young per brood (broods of up to 120 are common); gestation about 4 weeks (FishBase) to around 8 weeks (Seriously Fish).

Raising the fry

Fry are free-swimming at birth. Feed crushed flakes, baby brine shrimp and fine powder food. Move fry away from adults, or the adults will eat them.

Common mistakes
  • Keeping too many males, which stresses the females
  • Soft, acidic water
  • No hiding places, so the fry get eaten
Full breeding guide, day-by-day plan and simulator →

Where it lives in the wild

RegionCentral America and southern Mexico
Rivers and lakesAtlantic and Pacific drainages from Mexico to Colombia
HabitatCoastal rivers, lagoons and brackish waters
Native rangeAbout 1,500 km across
See it on the world map

Plants that suit it

Hygrophila polysperma

The story of the molly

Wild P. sphenops lives in fresh and brackish water from Mexico to Colombia and Venezuela. Shop mollies, including the black molly, are domestic hybrids; the original black molly was developed by a breeder in New Orleans and first exported from the USA to Germany in 1930. Hard water matters more than salt.

Achille Valenciennes described Poecilia sphenops in 1846. Most aquarium mollies are hybrids of several species, bred into black, dalmatian and other colours. Mollies tolerate brackish and even marine water.

First described by Achille Valenciennes in 1846.

  • Mollies can adapt to fully salt water.
  • The black molly is a captive-bred colour form.
  • Most shop mollies are hybrids of several Poecilia species.

Sources

16 facts checked with sources