Molly fish care guide

Mollies is a small group of live-bearing fish of the Poecilia genus (earlier, they were included with Mollienesia genus). They are rather popular and undemanding aquarium fish that even beginner aquarists can deal with. Due to selective breeding programs, many new variations were obtained, with different coloring and body shapes. They are all widespread and renowned tank dwellers, though quite often, they look very different. This is all due to their peacefulness, endurance, unpretentiousness, inexpensiveness, and easy breeding. Molly fish differ only in size and color, but the info about breeding, keeping, compatibility is the same for all of them.

Molly fish types

There are four mollies fish kinds in the wild:

All other fish variations with different body and fins shape and coloring are selective breeds obtained as a result of cross-breeding within the four basic kinds.

Scientific NamePoecilia, early Mollienesia
Common NameMolly, molly fish, black molly fish
Ease of keepingEasy
Lifespan5 years and more
Tank size50 liters (13 US gallons) and more
Tank typeCommunity of fishes
Temperature77-80,6 ºF (25-27 °C)
Water hardness10–20 dGH
Sizeabout 4-5 inches large (12.5 cm)

Molly Natural breeds

Common molly (Poecilia sphenops)

Common molly

This is the fish that black molly, the most popular tank fish, derived from. Nowadays, natural fish coloring isn’t almost encountered in aquariums since the wild species has less bright coloring, unlike its black variation. Its body is greyish-green on top with a slight light-blue tint, the body bottom is lighter, and the color varies from gray-white to silvery-blue. Dark spots of different color intensity are scattered over the fish body.

Poecilia sphenops have elongated, solid, and flattened from sides body with a round well-developed tail fin. The fins are small. Its mouth is meant for eating food from the water surface and algae scraping. The body size varies from 2 to 4 inches (5-10 cm). The females are larger than males.

Yucatan molly (Poecilia velifera)

Yucatan molly

A distinctive feature of this kind is a well-developed dorsal of the male species. The fin size may be up to 3 inches (4-5 cm) large and take most of the fish back. This is the largest molly, and its size may be up to 10 cm (4 in) large, while in the wild, it is up to 6 inches (15 cm). The tail fin has a rounded shape. The natural body color is silvery with horizontal dashed lines.

Due to its size, the fish requires spacious tanks. It is very active and needs space to swim. Also, be attentive when choosing its tank mates. Some fishes, such as tiger barbs, may nip molly’s fins.

Sailfin molly (Poecilia latipinna)

Sailfin molly

It is very similar to yucatan molly but smaller, and it has different coloring. The body is tall, elongated, solid, and flattened from sides. The dorsal is high and rectangular in shape, and it has 12-14 rays. The tail fin is round and well-developed.

In the wild, males’ size is up to 5 in (12 cm). However, usually, males in size are up to 3 in (7.5 cm), while mature females are up to 2.5 in (6.5 cm).

The coloring, in general, is bluish-grey. Males coloring has a green-blue tint with sparkling white spots on their sides that create rows. The body bottom is bright orange. The fins are blue with orange edges, colorful spots, and dashes.

Liberty molly (Poecilia salvatoris)

Liberty molly

For a long time, this fish has been considered a Poecilia sphenops’ variation, but currently, it has become a separate kind. It inhabits El Salvador waters. It can be quite seldom seen in tanks, even though it has an appealing coloring. Partially, this is due to its aggressive temper — the fish attacks both its relatives and other tank dwellers. Its body is silvery-yellow. It may have some light-blue tint. The abdomen and dorsal fins are very bright (red, black, or white).

Molly selective breeds

Selectionists constantly strive to create more and more new color variations of tank fish. They even conduct genetic experiments (for example, glofish). The same has happened to molly since this is a live-bearing fish which offspring is easy to get.

Black molly fish

Black molly fish
Black sailfin molly fish

This is the most famous, popular, and undemanding fish among all mollies. This fish is the best choice for beginner aquarists – black molly fish. It is less demanding, easier to breed, and requires a smaller tank capacity. In general, in this article, we’ll talk about black molly fish, though almost all we say is true for the other species.

The fish has an elongated body and a bit flattened from the sides. Its eyes and upward mouth are relatively large. The male fish grows up to 3 inches long (6–7.5 cm), and the female is about 4 inches large (10 cm) at the age of about 6 months. The beautiful fish fins get their maximum beauty and size only during the 2nd year of the fish life. Reference samples of black molly fish don’t have any glitter or spots on their body – they are coal-black.

Due to its coloring, black molly has been popular for many years.

In the wild, species with such coloring don’t exist. This color variation was obtained in the USA at the end of the 20s in the XX century. Sometime later, in Singapore, as a result of hybridization, lyretail mollies were obtained.

Black lyretail molly fish

black lyretail molly fish

These fishes with a lyre-shaped tail are also in great request. Their main distinctive feature is their tail fin structure. Its edge rays are longer than others, and they form a curve resembling an ancient musical instrument – a lyre. The coloring may vary. A huge number of color variations were bred, and none of them can be considered as the basic one.

In the process of hybridization with closely related species, such species as Poecilia sphenops and Poecilia velifera have also obtained a lyre-shaped tail. That’s why curren

Gold dust molly fish

Gold dust molly fish
Gold dust balloon molly

Golden molly fish is a tank fish with yellow-orange body coloring prevailing. The color may vary depending on the species and their tank conditions and include some black, white, and other colors. Tank conditions and care are the same as for any other molly. They are undemanding that can dwell in a wide variety of water parameters.

White molly fish

White molly fish

This is a generic term, and it is equally applicable to selective variations Poecilia velifera or Poecilia latipinna, as well as towards their hybrids. It is not encountered in the wild, and it was bred artificially. The main feature of the fish is its uniform silvery body coloring. The fins are semi-transparent with white speckles. Depending on the specific kind (Latipinna or Velifera), the adult species size will vary. The males are larger than females and have a large dorsal resembling a flag or a sail.

Dalmatian molly fish

Dalmatian molly fish
Dalmatian lyretail molly fish

This is black and white molly fish, which is an artificially bred color variation, and it’s not encountered in the wild. It has a unique body pattern – black spots and speckles on a white background that resemble the dalmatian dog’s color patterns. It is supposed that the variation was obtained based on the spotted Poecilia latipinna species.

Balloon molly fish

Balloon molly fish

A shortened body and a large abdomen characterize it. The body coloring may be different: orange, white, red, black.This is the weakest molly since its innards are lessened and pressed. The fish, as a rule, is more demanding to tank conditions (due to their curved spine), and their lifespan is seldom longer than 1.5-2 years. Nevertheless, these bright, barrel-like fishes can variegate your tank and are quite popular.

Gold Panda Molly fish

Gold Panda Molly fish
Gold Panda lyretail molly

This is a selective breed and quite a rare one. Intense yellow coloring merges into black near the fish’s tail. It has black eyes.

tly, the breed name has become a collective one and is equally used for all mollies with a similar tail fin structure.

Difficulties in keeping

The fishes are easy to care for and keep. They are a good choice for beginner aquarists. This is especially true for well-known and widespread black molly. You should be careful only with a balloon molly fish since, due to its curved shape, its lifespan is shorter than that of other molly species.


Poecilia sphenops have become the first described molly species. The description ws made by a French zoologist Achille Valenciennes in 1846 while working on his 22 books of “Histoire Naturelle des Poissons” (Natural History of Fish).

More than 50 years later, a renowned ichthyologist-classifier Charles Tate Regan described Poecilia salvatoris and Poecilia velifera basing on the sample study results in the British Natural History Museum.

In 1913 Poecilia latipinna was brought to Europe.

Since 1920 active work on selective breeding has started, and various hybrids appeared one after another. This was promoted by, first of all, the possibility of breeding between the three main molly kinds: Poecilia sphenops, Poecilia latipinna, and Poecilia velifera.

Habitat in the wild

Did you know that the molly genus (in Latin – Mollienesia) was abolished, and now all fishes from it are included in the livebearers genus (in Latin Poecilia). Well, I didn’t. I have found it only when preparing this article. And the fact that various fishes that we know as molly fishes are now also in this genus only adds more confusion.

Habitat is rather diversified – freshwater, brackish, saline water of different temperatures, hardness, and acidity. Various Poecilia fishes have some differences in their morphological characters. They’ve got used to different life conditions.

Wild molly kinds inhabit both freshwater and brackish waters through quite a wide territory. Its North border includes the South of Texas, while the southern border stretches along the Caribbean side of Colombia and Venezuela. Such a large habitat, including areas with quite different natural conditions, suggests the presence of many local forms of the kind which natural coloring essentially varies depending on the habitat.

As a result of the introduction, you can encounter the fish even on the other continents where they live and breed in conditions similar to their original ones. Thus, nowadays, there are local populations in Singapore, Japan, and some other places on our planet.

Sphenops molly fish is encountered in Mexico and Colombia waters, and sailfin molly can be found in channels with brackish water in Carolina state, Texas, Virginia, and Florida; yucatan molly can be seen only in Mexican peninsula Yucatan.

Keeping in a tank


How long does molly fish live? Its lifespan is approximately 4-5 years. It depends on the living environment and tank water temperature. The higher is the temperature, the faster is the metabolism and the lifespan decreases. However, provided with proper tank conditions, molly can live long and give birth to several fish generations during this time.

Tank capacity

In my opinion minimum tank size for the successful keeping of a small group of molly fish is 13 US gallons (50 liters). But these are active fishes. Therefore the perfect tank size for keeping them will be 26 US gallons (100 liters). Don’t keep the fish in small and crowded tanks. They may grow to become 10 cm long and will not feel comfortable in a small volume tank.

For yucatan molly, it’s better to select a twice larger tank since they are significantly larger than their relatives. They like swimming a lot, and for this reason, it is recommended to get a tank of classical rectangular shape with a lid: molly often jumps out from the water.

Water parameters and temperature

Mollies are quite enduring fish, and they can adapt to a wide range of water parameters. Yet, it is desirable to create optimal conditions in a tank.

There should be a stable biotic balance in a tank. All molly fishes are quite thermophilic, and they prefer a water temperature of about 23-27 °C. They don’t stand rapid temperature changes.

The tank water’s parameters may be quite various since molly fish adapts to any new conditions perfectly. However, the following parameters are recommended: water temperature 77-80,6 ºF (25-27 °C), ph: 7.0-8.0, water hardness 10 – 20 dGH.

Just like all other fishes, molly fish likes freshwater. That’s why it’s desirable to renew water systematically. Once a week, perform water renewal in the volume of ¼ from the whole tank capacity. This will ensure the absence of nitrogenous compounds of high concentration in the tank, such as ammonia, nitrites, and nitrates.

Water salinity

We should also mention that molly fish can live in brackish water as well, and in some resources, they even recommend putting some salt into the tank water intentionally. Well, this will not harm the fish, but don’t forget that this fish quite seldom inhabits without any tank mates, and the latter may not stand brackish water, or it could even be toxic for them. Therefore, I’d recommend adding some salt into the tank only if molly fish live alone or when they are in quarantine.

Filtration and aeration

Water filtration and aeration are required. It’s better if the tank is a thick planted one because molly fish like scrapping algae from tank plants.

Plants and decorations

Most of the time, the fish spends in upper and middle water layers. You also have to create open and well-lighted areas in the tank. Snags, stones, lots of plants should be present in the tank and provide the fish with some shelter if needed.

Black mollies are very useful in planted tanks because without damaging the plants. They keep them clean by eating algae from their leaves.

Mollies feel quite good in tanks with live plants. It’d be good to organize some thickly planted areas in the tank, but don’t forget to leave some free space for the fish to swim.

Tank mates

Molly fish is a very active one, and it is considered a peaceful one, though I’d rather say that it is a moderately aggressive one. Yes, in a roomy tank, it behaves very peaceful and calmly, but if the tank is small and crowded, the fish can show aggression towards its kind and sometimes to other fishes in the tank.

It’s better to keep back molly fish in a group where females prevail. This is a common rule for all live-breeders since when the number of males is equal to or higher than that of the female fish, the latter will always be stressed due to the males haunting them all the time.

The fish can live both in a common tank and separately. It gets on well with various tank mates. In general, tank mates have to be approximate of a similar size. Molly fish have good relationships within their group – they almost don’t show any intraspecific aggression. But at the same time, if the tank is small, the males may haunt each other. That’s why it’s better to have a spacious tank so that at least 2 gallons (10 liters) of water would fall for one fish.

When selecting tank mates, let them be of a similar size. Mollies get on well with other live-bearing fishes such as (guppy, Endler’s guppy, platy, swordtail), characins (black neon tetra, cardinal tetra, ember tetra, flame tetra, neon tetra), rasboras (harlequin rasbora), danios (zebrafish), corydoras (Corydoras julii, panda cory, pygmy cory, Adolfo’s catfish), plecos (bristlenose pleco). They can live together with barbs (tiger barb, cherry barb, Odessa barb, rosy barb); Poecilia velifera is the only exception – the males’ long fins may be nipped in this case. When keeping mollies with other fishes, the tank should be spacious, and it should have enough shelters. It’s not recommended to keep even large molly species with aggressive cichlids (like Jack Dempsey fish, jaguar cichlid, texas cichlid, flowerhorn).

If you want all mollies in the tank to have the same appearance, don’t keep different fish kinds together in the tank to avoid cross-breeding.


This is an omnivorous fish that eats all types of live, frozen, or artificial food. However, molly fish needs a large amount of food with vegetable fibers component, for example, with algae or vegetables. In the wild, molly fish has lots of algae in its diet. You can see it from the fish lips and behavior. You can often see how it scrapes algae and fouling from tank glass and decorations.

As for the fish food with vegetable components, it’s better to feed molly fish with molly flakes, or you can give it pieces of boiled cucumbers, squash, lettuce leaves. Live food you may add to the fish diet is bloodworm, tubifex, brine shrimp. In general, feeding molly fish isn’t complicated. The main thing is to remember that the vegetable component is very important in the fish diet.

Feeding them with quality artificial food is the best option since this food is well-balanced, has all necessary vitamins, and digest well. Such food is easier to serve and store.

You should feed them several times a day. The food portion should be enough to be eaten by the fish in several minutes. We should mention that mollies are prone to overeating, so the food portions must be small.

Gender differences: male vs female

It is quite simple to see between the male and female fish. Molly fish females are larger, and they have large rounded abdomen. The most certain difference you can use to identify the fish’s gender is the shape of the anal fin – the male fish has its anal fin modified into a tube (gonopodium), and the female’s anal fin is of triangle shape.


Molly fish is a live-breeder just like a guppy, which means that the juveniles are spawned into the tank is completely formed, and they skip the egg stage. You don’t need any special conditions for breeding. It’s quite enough to keep males and females together in a common tank.

Provided with comfortable tank conditions, molly fish spawns every month. When mating, the male fish uses its gonopodium, which has a tube to transfer ejaculate to the male fish, and hooks closer to the female when fertilizing her, which increases chances of successful fertilization. The fish males become reproductive at about 12 months, and females when being 6 months old.

Mollies can breed both in community tanks and in a separate spawning tank. However, the latter is more preferable because tank mates in the community tank may eat the juveniles. The female ready for spawning should be put in a tank of at least 5 liters capacity. In large tanks, the fish will be too stressed. Put some shelters and plants into the spawning tank, and they will become shelters for the offspring. Sadly, parents can eat their juveniles as well.

The female fish carries eggs for about 35 – 45 days. It’s difficult to see if the female fish is pregnant, especially in black molly fish.

As for the pregnancy signs – they are the enlarged abdomen, and the female fish starts to look for shelter in some dark corners of the tank. It’s desirable to put such a female fish into a separate spawning tank where water parameters will be the same as that of the common tank.

Usually, spawning occurs in the early morning. Large-sized female fish may spawn up to a hundred juveniles at once. The number depends on female fish age and size. Molly fish juveniles are born rather large. They don’t get up from the tank bottom right away and stay there or on the leaves of tank plants for a while. Molly fish juveniles are very sensitive to tank water contamination. That’s why it’s recommended to renew the water in the tank with juveniles more often than usual.

To grow fast, the juveniles need to have a diversified diet. They are fed with milled high-quality artificial food or special food for fry.