Mollies are active, hardy livebearers native to the Americas. They are famous for their ability to adapt to fresh, brackish, and even full marine water. They are voracious eaters (including algae) and produce a high bioload for their size. Note: 'Molly' covers several species; the Short-finned (*P. sphenops*) and the much larger Sailfin (*P. latipinna* and *P. velifera*).
Molly (Sailfin/Black/Dalmatian) At a Glance
Molly (Sailfin/Black/Dalmatian) Tank Requirements
Will Molly (Sailfin/Black/Dalmatian) fit in your tank?
Care guides tell you what Molly (Sailfin/Black/Dalmatian) needs, the next question is whether your tank can safely provide it. Test Molly (Sailfin/Black/Dalmatian) against your tank size, maintenance needs, and the fish you already keep before you buy.
Useful setup supplies
We may earn from qualifying purchases
Molly (Sailfin/Black/Dalmatian) Water Parameters
Water care products
We may earn from qualifying purchases
Molly (Sailfin/Black/Dalmatian) Temperament & Compatibility
Molly (Sailfin/Black/Dalmatian) Varieties
Each variety inherits the species defaults above. Only differences are highlighted.
Short-Finned (Standard)
The standard *Poecilia sphenops*. Stocky but agile. Males may harass females constantly; a ratio of 1 male to 3 females is recommended to disperse stress.
Differs in 3 traits from base species
Also known as: Black Molly, Dalmatian Molly, Gold Molly, P. sphenops
Sailfin Molly
Significantly larger than standard mollies with a spectacular dorsal fin. Requires more swimming space and stable vegetable matter in their diet.
Differs in 4 traits from base species
Also known as: P. latipinna, P. velifera, Green Sailfin, Giant Sailfin, Yucatan Molly
Balloon Molly
A man-made morph with a deformed spine resulting in a round, balloon-like body. They are prone to swim bladder issues and digestive problems. They cannot swim as strongly as standard mollies.
Differs in 4 traits from base species
Also known as: Potbelly Molly
Molly (Sailfin/Black/Dalmatian) Care Guide Summary
The Molly (Sailfin/Black/Dalmatian), scientifically known as Poecilia sphenops, belongs to the Livebearers family group. Adults reach a maximum size of approximately 10 cm and have a fusiform body shape with a fast growth rate. Classified as mostly peaceful, this species primarily occupies the surface and mid-level zones of the aquarium and produces a high level of biological waste.
To thrive, the Molly (Sailfin/Black/Dalmatian) requires a brackish tolerant aquarium with a minimum volume of 75 litres and a tank length of at least 60 cm. Water temperature should be maintained between 24°C and 28°C, with a pH range of 7.5–8.5 and a general hardness of 12–30 dGH. A moderate water flow is preferred.
The Molly (Sailfin/Black/Dalmatian) is a rewarding species to keep, provided its core environmental needs are met. This species is available in 3 varieties: Short-Finned (Standard), Sailfin Molly, and Balloon Molly. Each may differ slightly in size, temperament, or care needs, so it is worth checking the specific requirements of the variety you plan to keep.
Molly (Sailfin/Black/Dalmatian) Habitat Setup
When setting up an aquarium for the Molly (Sailfin/Black/Dalmatian), a moderate water flow best suits their natural preferences. Because this species occupies the surface and mid-level zones, the aquarium layout should prioritise adequate surface area with floating cover to make them feel secure near the waterline and open swimming space in the centre of the tank for free movement. Useful additions include an established tank with natural algae growth, as they depend on it as a primary food source and dense planting to provide cover, break sightlines, and reduce stress.
Molly (Sailfin/Black/Dalmatian) Compatibility Notes
Classified as mostly peaceful, the Molly (Sailfin/Black/Dalmatian) is a social species that requires the company of its own kind to thrive. When choosing tankmates, shy or slow-feeding tankmates may be outcompeted at feeding time and their energetic swimming style may stress more sedentary or timid species. Selecting tankmates that favour different water layers from the surface and mid-level zones can help reduce competition and territorial overlap.
Molly (Sailfin/Black/Dalmatian) Recommended Tank Sizes
Standard aquarium sizes that meet the minimum volume and length requirements for Molly (Sailfin/Black/Dalmatian).
20 Gallon High
20 Gallon Long
29 Gallon Standard
30 Gallon Breeder
36 Gallon Bowfront
40 Gallon Breeder
Show 17 more tank sizes
Molly (Sailfin/Black/Dalmatian) Feeding & Diet Considerations
The Molly (Sailfin/Black/Dalmatian) will eat fry, so breeding efforts in the same tank are unlikely to succeed and is an aggressive eater that may prevent timid tankmates from getting enough food, so target feeding or simultaneous feeding at opposite ends of the tank can help.
Feeding products
We may earn from qualifying purchases
.webp?2026-04-25T14%3A35%3A38.022Z)
Frequently Asked Questions About Molly (Sailfin/Black/Dalmatian)
How big does Molly (Sailfin/Black/Dalmatian) get?
Molly (Sailfin/Black/Dalmatian) (Poecilia sphenops) typically reaches a maximum adult size of approximately 10 cm. They have a fusiform body shape and a fast growth rate.
What tank size does Molly (Sailfin/Black/Dalmatian) need?
A minimum aquarium volume of 75 litres and a tank length of at least 60 cm are recommended for Molly (Sailfin/Black/Dalmatian). This ensures enough swimming space and helps maintain stable water conditions.
What water parameters does Molly (Sailfin/Black/Dalmatian) need?
Molly (Sailfin/Black/Dalmatian) thrives in brackish tolerant conditions with a temperature range of 24–28°C, a pH between 7.5 and 8.5, and a general hardness of 12–30 dGH. A moderate water flow is preferred.
Is Molly (Sailfin/Black/Dalmatian) peaceful or aggressive?
Molly (Sailfin/Black/Dalmatian) is classified as mostly peaceful with an aggression score of 3 out of 10. They are generally well-suited to peaceful community tanks.
Can Molly (Sailfin/Black/Dalmatian) live alone?
No, Molly (Sailfin/Black/Dalmatian) should be kept in groups of at least 3 to reduce stress and encourage natural behaviour.
Does Molly (Sailfin/Black/Dalmatian) have any special tank requirements?
Yes. Molly (Sailfin/Black/Dalmatian) benefits from plants - densely covered and established algae (otocinclus) in the aquarium. These features help replicate their natural habitat and promote overall health and well-being.
Top Tank Mates for Molly (Sailfin/Black/Dalmatian)
These fish are strong compatibility matches for Molly (Sailfin/Black/Dalmatian) based on water preferences, temperament, adult size, and tank behavior.
Ghost Shrimp
Palaemonetes paludosus
Ideal Tank MatesFiddler Crab (Brackish)
Uca sp.
Ideal Tank MatesAssassin Snail
Anentome helena
Ideal Tank MatesBumblebee Goby (Brackish)
Brachygobius xanthozonus
Ideal Tank MatesOrange Chromide
Etroplus maculatus
Ideal Tank MatesNeon Blue Cichlid
Paracyprichromis nigripinnis
Ideal Tank MatesPlants That Suit Molly (Sailfin/Black/Dalmatian)
These plants pair well with Molly (Sailfin/Black/Dalmatian) based on shared water preferences, layout fit, and how likely they are to hold up in the same aquarium.
Afzel's Anubias
Anubias afzelii
Amazon Sword
Echinodorus amazonicus
Anacharis
Egeria densa
Anubias Barteri
Anubias barteri
Baby Tears
Lindernia rotundifolia
Balansae
Cryptocoryne crispatula
Fish Similar to Molly (Sailfin/Black/Dalmatian)
Dwarf Molly
Poecilia chica
The Dwarf Molly is a rare and peaceful livebearer native to Mexico. It is the smallest member of the True Mollies. They thrive in strictly freshwater environments without the need for added salt, provided the water is hard and alkaline. They are active, constantly grazing on algae, and should be kept in groups with a higher ratio of females to males to reduce reproductive harassment.
Balloon Molly
Poecilia latipinna hybrid
A selectively bred morphological variant characterized by a shortened spine and a rounded, balloon-like belly. Due to their altered anatomy, they are poorer swimmers than standard mollies and are prone to digestive and swim bladder issues. Like all mollies, they thrive in hard, alkaline water, appreciate algae in their diet, and are highly tolerant of brackish conditions.
Dusky Millions Fish
Phalloceros caudimaculatus
A highly adaptable, sub-tropical livebearer native to South America. Known for its hardiness, it thrives in unheated aquariums and can tolerate mildly brackish water. Unlike many common livebearers, they are voracious algae grazers and may damage soft-leaved plants. Males relentlessly pursue females to mate, so keeping a ratio of at least 2-3 females per male is strongly advised.
African Butterfly Fish
Pantodon buchholzi
A fascinating, prehistoric-looking surface dweller native to the slow-moving waters of West Africa. They are strictly top-dwelling ambush predators with a completely flat back and upturned mouth designed to hunt insects and small fish. A tight-fitting lid is absolutely mandatory as they are exceptional jumpers capable of gliding above the water.
Mosquitofish (Gambusia)
Gambusia affinis
An extremely hardy livebearer historically introduced worldwide for mosquito control. In the aquarium, they are notorious fin-nippers and highly aggressive towards other small fish. They are best kept in species-only setups or indoor/outdoor ponds. Males are significantly smaller than females.
Harlequin Rasbora
Trigonostigma heteromorpha
A highly popular, peaceful schooling fish recognizable by its metallic copper/orange body and the distinct black triangular 'porkchop' patch on its hindquarters. Originating from peat swamps and blackwater streams in Southeast Asia, they are active swimmers that thrive in heavily planted aquariums with gentle to moderate water flow.