Shortfin molly
Poecilia mexicana
Also known as Atlantic molly, Poecilia mexicanus
FreshwaterBrackishFish
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
- Family
- Poeciliidae
- Origin
- Mexico, Guatemala
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.
Weekly picks
Tank mates
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.
Blackwing hatchetfish
Carnegiella marthae
Freshwater1.4 in (3.5 cm) · 30 gal (115 L)68–82°F (20–28°C)
Firemouth cichlid
Thorichthys meeki
Freshwater5.9 in (15 cm) · 30 gal (115 L)73–82°F (23–28°C)
Red-spotted tetra
Copeina guttata
Freshwater3.9 in (10 cm) · 32 gal (120 L)73–82°F (23–28°C)
Marbled hatchetfish
Carnegiella strigata
Freshwater1.6 in (4 cm) · 32 gal (120 L)68–82°F (20–28°C)
Bugeye squeaker
Synodontis contractus
Freshwater3.9 in (10 cm) · 30 gal (114 L)72–79°F (22–26°C)
Slender rasbora
Rasbora daniconius
Freshwater3.9 in (10 cm) · 32 gal (120 L)72–81°F (22–27°C)
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.
How big does a Shortfin molly get?
An adult Shortfin molly reaches about 4.3 in (11 cm).
Related species
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Poecilia gillii
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Poecilia formosa
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Poecilia vivipara
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