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Platy And Molly: What Are Their Key Differences And Similarities?

Although platy and molly fish may appear similar at first glance they have a number of key differences. So how do you tell them apart?

By Julie Millis
Last updated on

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platy and molly
Southern Platy (Xiphophorus maculatus)

Platy and molly fish are very peaceful tank inhabitants, and with their wide range of colors and variations, they can make beautiful additions to your community aquarium. But at a glance these fish can appear very similar, so how do you really tell them apart?

Between the team and I, we’ve kept several varieties of platy and molly fish over the years. And there are actually several differences between the two when you know what to look for!

You’ll find differences in their appearance, size, diet, breeding traits, lifespan, and preferred tank conditions.

So keep reading if you want a full guide on how to tell a platy and molly apart, where we’ll cover all these in detail along with much more!

What Is A Platy vs. A Molly?

Platy and molly fish come from the same family, Poeciliidae, and while may look similar they have several key distinctions.

Average Size:c. 1.6 to 2.8 inchesc. 3.2 to 4.8 inches
Average Lifespan:c. 3 to 4 yearsc. 3 to 5 years
Appearance:Shorter, rounder body shape. Warm colors like orange, red and yellow. Fan-shaped tail. Front facing mouth.Elongated body. Colors often include silver and black. Larger, angular fins. Upward facing mouth.
Temperament:Peaceful, can be aggressive when breeding or if kept in poor tank conditionsPeaceful, show some aggression in an overcrowded tank
Minimum Tank Size:10 gallons20 gallons
Water Conditions:Fresh, hard water (GH 10 to 28, KH 3 to 5), pH 7.0 to 8.0, temperature 70 to 80°FFresh or brackish, hard water (GH 12 to 25, KH 15 to 30), pH 6.5 to 8.5, temperature 75 to 80°F

The table above gives an overview of the key differences, along with some similarities. But bear in mind as there are many different species of platy and molly fish these can sometimes vary. Sailfin Mollies (Poecilia latipinna), for example, can grow up to 6 inches in rare cases [1].

Origins Of The Platy And Molly

While platy and molly fish both sit under the Poeciliidae family, they come from two distinct genera. Platy fish are classified under the Xiphophorus genus which was first described by Heckel in 1848 [2].

Several species of molly fish, including the Common Molly (Poecilia sphenops), have been described under the subgenus of Mollienesia [3]. But it’s now more common to refer to them using their genus of Poecilia, to which guppies and Endler’s livebearer also belong [4].

Platyfish originate from the Coahuila region of northeastern Mexico down to Honduras [5]. One key species, the Southern Platyfish (Xiphophorus maculatus), is mainly found in the Veracruz region of Southern Mexico [6].

Mollies inhabit fresh and brackish waters in similar regions. The Common Molly ranges from north of Veracruz City to Guatemala [7], whereas the Sailfin Molly inhabits several regions of the Southern United States along with the Mexican Yucatan Peninsula [8].

Livebearers And Their Breeding Cycle

Both platy and molly fish are livebearers, so give birth to live fry rather than laying eggs. The males of platy and molly fish both have gonopodia, a modified rod-like anal fin that they use to inseminate the females.

Once insemination has taken place, the gestation period for most molly fish including the Common and Sailfin Molly is around 3 to 4 weeks [9,10]. Similarly, the interval between broods in Xiphophorus fish, including platies, is about 28 to 30 days [11].

Are Swordtails Considered As Platy Or Molly Fish?

While swordtail fish are also livebearers and members of the Xiphophorus genus along with platyfish, they are made up of several separate species. Swordtails also have an elongated tail fin, as their name suggests, whereas platyfish species lack this ‘sword’ [12].

Although swordtails are generally peaceful fish they can become aggressive during breeding, particularly towards other livebearers. So we generally don’t recommend you keep them with platy and molly fish in the same tank.

What Are the Differences Between A Platy And Molly?

As well as platy and molly fish coming from distinct genera, they also have a number of differences in their appearance, behaviors, and breeding habits.

black and gold Sailfin Molly
Sailfin Molly (Poecilia latipinna)

Differences In Appearance

You may think platy and molly fish appear very similar at first glance, but if you look closely there are actually several key differences.

  • Shape & Size: Platyfish have a shorter, rounded body whereas mollies generally have oblong, elongated body shapes. Platies are also smaller, with an average length of around 1.6 to 2.8 inches, while mollies tend to range from 3.2 to 4.8 inches [13, 14].
  • Color: Platyfish have been bred to produce warm colors like orange, red, yellow, or gold. Although platies in the wild, such as the Southern Platyfish are yellowish-beige to olive-grey [15]. Molly colorations include silvers, yellow-orange, and black [16].
  • Fins & Tail: Platyfish have smaller fins than mollies, with a distinct fan-shaped tail fin in most cases. Mollies have larger, more angular fins, particularly their dorsal fin which runs along their back.
  • Jaw: In many cases, you can also tell platy and molly fish apart from their jaws. Most platyfish have forward-facing mouths, whereas mollies tend to have a mouth that faces upwards. In the wild, this helps them scrape algae from surfaces [17].

Behavioral Differences

Platies are social fish and like to shoal together, so keep them in a group of 5 or so. They are, however, active breeders and can become aggressive if there aren’t enough females in your tank. So aim to keep a ratio of about 1 male to 3 females.

Molly fish are very rarely aggressive, and shoal in a similar way to platyfish. So keep at least 3 or 4 mollies together in your tank. While they don’t tend to be as aggressive during breeding, keep them in a similar 1-to-3 ratio to avoid the males stressing the females.  

Will A Platy And Molly Get Along?

Yes! As platy and molly fish are both peaceful and of similar temperaments, they will get along fine, as long as you keep them under the right conditions.

Mollies tend to prefer more cover and hiding spaces than platies, who are happier to swim out in the open towards the top of your tank. So if keeping them together, make sure you have a well-planted tank for your mollies.

Whilst we’ll come on to platy and molly tankmates later, make sure you avoid larger aggressive fish like cichlids or fin-nippers that could become confrontational particularly towards your mollies with their long fins.

Male vs. Female Platy And Molly Fish

Telling male from female platy and molly fish can be one of the easier differences in appearances to spot. 

Male vs. Female Platies

One of the easiest ways you can tell male platyfish from females is to look at their undersides. The anal fin near the tail in female platies tends to be a fan shape, whereas males have a rod-like gonopodium for breeding.

Male platies are also brighter and more colorful than females to help them during courtship and selection when breeding.

Male vs. Female Mollies

Female mollies are bulkier than males with their sleeker, torpedo-shaped bodies. Males, such as the Sailfin Molly, also have a larger dorsal fin on their back than the females [18]. In the same way as platies, you’ll notice male mollies tend to be brighter in color than females.

The anal fins on the underside of male and female mollies are different too. Female mollies tend to have a triangular anal fin, while males have the longer rod-shaped gonopodium.

Differences In Breeding

Platy and molly fish are both prolific breeders. So if you don’t want offspring it’s best to keep females only. Whilst platy and molly fish are peaceful, they can become more aggressive in an all-male tank when trying to establish dominance.

In general, platyfish breed more readily than mollies but each brood is smaller at around 20 to 80 fry at a time. Once the female has been inseminated gestation is around 4 weeks. And while adult platies don’t tend to eat their fry, it’s still best to isolate the female while she gives birth.

Molly fish, like the Common Molly, produce broods of between 10 and 140 live young, and gestation can vary between 3 to 4 weeks. Female mollies can also store sperm in their bodies and produce several broods a year without mating again [19]. 

Unlike platies, molly fish can eat their own fry so if you want to raise them successfully you’ll need to separate the adult fish from them using a breeding box or separate tank once the female has given birth.

Can Platy And Molly Fish Crossbreed?

As platy and molly fish come from two distinct genera, Xiphophorus and Poecilia respectively, they cannot crossbreed. Even if platy and molly fish were to mate, their genetic material is too different to be able to produce viable fry.

On the other hand, crossbreeding between species within each genus is possible and happens frequently. Many aquarium varieties of platyfish, for example, are actually hybrids of the Southern Platyfish and the Variatus Platy (Xiphophorus variatus).

Platies can also crossbreed with swordtails like the Green Swordtail (Xiphophorus hellerii). And while this has been selectively done within science to study some genetic disorders, you can generally breed them in your aquarium with no ill effects [20].

Care Differences Between A Platy And Molly

There are actually several similarities in the care you need to give platy and molly fish, but there are also a number of subtle differences.

black molly fish in aquarium
Black Molly (Poecilia sphenops)

Differences in Tank Care

While you can keep platy and molly fish together they do have slightly different ideal tank conditions. 

What Size Tank Do A Platy And Molly Need?

Platy and molly fish need plenty of space to swim and explore. The general rule for most freshwater fish is to allow 1 gallon for every inch of fish. So if you keep a shoal of 5 two-inch platies you’ll need a minimum of a 10 gallon tank.

Similarly, to keep 4 five-inch mollies you’ll need a 20 gallon aquarium. But bear in mind mollies are a little shyer than platies and prefer a well-planted tank. So make sure you’re tank is large enough for vegetation and decorations to allow for cover.

Platies will tend to spend time towards the top of your tank, whereas mollies will swim in the middle or even occasionally near the bottom. So for both fish, a longer horizontal tank is better rather than a tall vertical one.

What Type of Water Do A Platy And Molly Need?

Whilst platy and molly fish both have ideal water conditions these do overlap, so you can keep them together in your home aquarium.

Whilst aquarium-bred platies are quite adaptable, their natural waters in Southern Mexico are fairly hard and alkaline. Ideally, they should have a general hardness (GH) of around 10 to 28 and carbonate hardness (KH) of 3 to 5. A slightly alkaline pH of 7.0 to 8.0 is preferred.

Again, mollies need hard water with a GH of about 12 to 25 and KH of 15 to 30. They won’t do well in soft water so if yours isn’t hard enough you’ll need to use mineral supplements. A slightly alkaline pH of around 6.5 to 8.5 is also preferred by molly fish.

Although mollies in the wild often come from areas of brackish water they can do just as well in freshwater, and indeed many aquarium-bred mollies are more used to it. But note if you buy imported mollies they are more likely to have been bred under brackish conditions.

If this is the case, you can start by adding aquarium salt to your tank before gradually reducing it. A salinity test kit will help you to monitor and adjust your water as you go. But remember you are only likely to need to do this with imported molly fish.

How To Raise The pH For Livebearers

If you do live in an area of soft water and need to raise your pH so it’s more alkaline for your platy and molly fish there are a few ways you can do this. Firstly, you can use a mineral buffer such as Seachem Alkaline Buffer to bring your pH to around 7.2 to 8.5.

An alternative is to add crushed coral or shells to your substrate. Take care with this method though as it can be difficult to control the pH level. Use a small amount at a time and use a test kit to monitor your pH.

What Heating And Filtration Do A Platy And Molly Need?

As platy and molly fish come from similar tropical waters of the Southern United States and Mexico, they also have similar needs when it comes to heating your tank. Platies need warm water between 70 and 80°F, and mollies prefer around 75 to 80°F.

So if you keep platy and molly fish in the same tank you can set your heater to about 75°F which will be fine for them both. There are several excellent digital aquarium heaters for small and larger fish tanks which allow you to set the correct temperature to within +/- 0.5 degrees.

Platy and molly fish can be messy and produce quite a lot of waste. To keep your tank clean and prevent ammonia from building up you’ll need a filter with biological filter media. This will allow beneficial bacteria to colonize and break down this ammonia via the nitrogen cycle.

Difference Between Diets In A Platy And Molly

Platy and molly fish are both omnivores and need a balanced diet consisting of plant material as well as meat. Yet there are some subtle differences between the two.

Platies will graze on vegetation in the wild, along with small insects and fry. You’ll need to provide them with more plant material than meat, so spirulina and high-quality fish flakes are a good choice. You can give them frozen bloodworms, tubifex, or brine shrimp once a week too.

Mollies will eat a similar diet of flake food, spirulina, and frozen daphnia. But the main difference comes in the frequency of feeding. 

As mollies are particularly greedy you should feed them twice a day, and only give them what they can eat in 2 minutes. In contrast, you can feed platies up to 3 times a day for around 3 minutes at a time.

Common Illnesses Between A Platy And Molly

Platy and molly fish can be susceptible to several common fish diseases that affect numerous aquarium fish species. We’ve outlined the main ones affecting both types of fish along with symptoms to look out for and treatments.

  • Ich (White Spot): Caused by a protozoan and common in platy and molly fish, Ich symptoms include white spots on the gills and body. Ich-X or API White Spot Cure can be effective treatments.
  • Velvet: This disease can be quite serious if left untreated and appears as gold-colored specks on the body of your platy or molly fish. It is caused by a parasite, Oodinium spp., and products such as SeaChem Cupramine can be used to treat it.
  • Fin Or Tail Rot: This appears as decay at the edges of your platy or molly’s fins or tail and is caused by bacterial infection. You can use antibacterial treatments like API Fin And Body Cure or Seachem Kanaplex.
  • Mouth Fungus: a.k.a Columnaris, mouth fungus causes cloudy patches on the mouth or gills. It’s caused by the bacterium Flavobacterium columnare and can be fatal if left untreated. Again, API Fin And Body Cure or Seachem Kanaplex can be effective.
  • Swim Bladder Issues: These issues can result in your platy or molly swimming upside down. They’re common in Balloon Mollies and can be caused by poor water conditions, though the direct cause can be difficult to diagnose so it’s best to consult a vet.

Platyfish can also be susceptible to ammonia or nitrite poisoning if the levels are too high in your aquarium. This can often happen when setting up a new tank if it has not had time to fully cycle and establish the right water parameters.

What Are The Different Kinds Of Platy And Molly?

Aquarium breeders have produced countless hybrids of platy and molly fish leading to many gorgeous variations of each type.

red and black mickey mouse platy fish
Mickey Mouse Platy (Xiphophorus maculatus)

Popular Varieties Of Platyfish

Most varieties of platyfish are hybrids of the Southern and Variatus Platy, but extensive crossbreeding within the aquarium industry has produced many beautiful and brightly colored varieties. We’ve covered some of the most common here.

  • Rainbow Platy: The Rainbow Platy has bright and often shimmering coloration in different shades of yellows, reds, oranges, blues, and greens. One of the smaller platies, this variety does well in a planted tank and is very peaceful.
  • Mickey Mouse Platy: This variety is so called as it has a 3 spot pattern near the tail in the shape of Mickey Mouse! Often found in red or blue, this platy can tolerate a range of water conditions.
  • Wagtail Platy: Most commonly coming in red or gold, these platyfish are distinguished by their jet-black tail fin and dorsal fin on their back. They are hardy and active fish and another of the smaller platy varieties.
  • Tuxedo Platy: Tuxedo platies come in a wide range of colors and have a lighter front end with a darker posterior. Some varieties also have metallic specs over their back.
  • Pintail Platy: Whilst rarer than some of the other platies above, pintails are a beautiful variety so called because their tail has an elongated mid-section. They come in a range of types including rainbow, red, platinum-green, gold, and panda.

Popular Varieties Of Molly Fish

In a similar way to platyfish, aquarium crossbreeding has given rise to many variations of molly fish with amazing colors and styles. A few of the most popular are featured below.

  • Common Molly: The Common Molly is one of the smallest varieties with males reaching around 3 inches. Whilst the wild variety tends to be gray, aquarium-bred mollies have given rise to many colors including orange, red, black, and yellow.
  • Sailfin Molly: One of the larger molly fish at around 5 inches, Salfin Mollies have a large rectangular-shaped dorsal fin on their back like a sail. They come in several colors with black or spotted being common.
  • Black Molly: This molly fish is entirely black as the name suggests. Its body, fins, and even its eyes are a deep black color. Black Mollies are generally peaceful although several males in the same tank can become aggressive.
  • Balloon Molly: These are shorter than other mollies with a round belly that gives them their name. Balloon Mollies are peaceful, social, and like to shoal. They will tend to swim in the middle of your aquarium and prefer a well-planted tank.
  • Dalmatian Lyretail Molly: These are a variation of Salfin Mollies, but with a distinct lyre-shaped tailfin. As their name suggests, they also feature the Dalmatian black and white speckled appearance across their body.

What Are The Best Tank Mates For Platy And Molly Fish?

Platy and molly fish are both peaceful and social fish and you can pair them with a range of tankmates in your community tank. Here are a few examples.

  • Other Livebearers: These can make great tankmates including other platy and molly fish as most species are peaceful and will get along well. Be aware if you keep guppies or Endler’s Livebearer with mollies they can interbreed.
  • Bottom Dwellers: Catfish including Sterba’s Cory, Otoclinus, and Bristlenose Pleco can be a great choice as they are peaceful too. They will stay at the bottom of your tank avoiding platy and molly fish that will usually stay in the mid-tank and higher up.
  • Barbs: Peaceful barbs such as the Cherry Barb or Odessa Barb can work well with platy and molly fish. Do stay away from aggressive ones like the Tiger Barb though.
  • Tetras: Several species of tetra can be far too aggressive for platy and molly fish so use caution here. Avoid Blue Tetras, White Spot, and Black Widows. Smaller, peaceful varieties such as the Emporer Tetra can make good tankmates though.
  • Gouramis: Smaller, peaceful gourami such as the Honey Gourami can make great tankmates for platy and molly fish. But make sure you research any gourami species you plan to keep as some can be aggressive. 

When choosing tankmates for platy and molly fish always avoid aggressive species like cichlids, angelfish, and butterfly fish. These can cause stress to your platy or molly and in turn, it can become more aggressive too.

What To Do Next?

As peaceful and sociable inhabitants, and with a wide range of varieties and colors, platy and molly fish are fantastic additions to your freshwater tank.

And if you want some ideas to expand your community aquarium with other amazing species, check out our guide to 41 cool freshwater fish too.

Here, you’ll find all you need to know about the ideal tankmates whether you plan to keep platy of molly fish or both!


We’ve answered some of the most frequently asked questions when it comes to platy and molly fish. Just take a look below!

Are Platy And Molly Fish Easy To Breed?

Yes! Both platy and molly fish are prolific breeders so if you don’t want any fry it’s best to keep all females. Platy and molly fish cannot crossbreed though.

What Fish Can Breed With A Platy And Molly Fish?

Platyfish can interbreed within their genus including other platy species and swordtails. Similarly, different molly species such as Common Mollies and Sailfins can interbreed.

Can A Platy And Molly Live With Guppies?

Platy and molly fish can live with guppies as they all have peaceful temperaments. But be aware if you keep mollies with guppies it is possible for them to interbreed.

How Long Do A Platy And Molly Live?

Platy and molly fish have similar lifespans in your aquarium. If kept under the right conditions platies will generally live between 3 to 4 years, while mollies will live for 3 to 5 years.

Photo of author
Julie Millis
Julie has been involved in aquatics for over 15 years. She is passionate about freshwater and saltwater tanks. Julie loves helping with all your fish-keeping questions!

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