Mollies – Care guide, breeding & species overview

In the world of freshwater aquarium fish, the Molly Fish is a firm favourite due to its delightful appearance and low maintenance attitude. While the Molly is easy to look after, there are some things you need to know in order to keep your pet healthy and happy and, so, we’ve put together our ultimate guide to taking care of Molly.

Facts & Overview

Before we get onto the nitty gritty of taking care of your fish, we’ll start with the basics: 

Official NamePoecilia sphenops
Ease of careEasy
TemperamentPeaceful / Non aggressive
ColourThe Molly is available in a number of different colours, including black, white and orange – see appearance section below
LifespanApproximately five years
SizeThe Molly will usually grow to around 4.5 inches in captivity
OriginSouthern United States, Central America, The Yucatan peninsula in Mexico, 

Types of Molly Fish

There are a few varieties of Molly Fish to choose from, and these are: 

  • Lyretail Molly Fish – This variety is easy to recognise due to its long, flowing caudal fin, dorsal fin and anal fin – all of which taper off into a point. 
  • Sailfin Molly Fish – This type of Molly tends to be larger and taller than its compatriots and is distinctive due to its sailfin (a wave shaped fin which runs from the head to the tail). 
  • Balloon Molly Fish – As the name suggests, the Balloon Molly Fish is plump with a round belly and is usually black, yellow or white. 

Molly Fish Appearance

As we’ve mentioned above, the Molly Fish comes in a number of colours, including: 

  • White with red eyes (albino)
  • Black with orange detail on the tail fins
  • Brown
  • Orange (red or orange in colour)
  • Gold
  • Dalmatian – white or silver with black speckles

The black Molly Fish is particularly interesting as no other species achieves this very dense shade of black. 

Sex and pregnancy

It’s quite easy to tell the sex of a Molly Fish as the male is usually considerably larger than the female and features a sailfin (a fin which runs from the head to the tail) which is not present in the female.

When pregnant, the female Molly Fish will become plumper and will develop a dark coloured spot on the base of the anal fin. 


When it comes to caring for your Molly Fish, your first port of call is, of course, the tank. To keep your Molly Fish comfortable, with enough room to roam about, you’ll need a tank of at least 10 gallons in size. If you have three or more fish, you should double the size of your tank to prevent problems. 

Furnishing your tank

As with many freshwater fish, you’ll need to line your tank with a substrate. Molly Fish will be happy with either sand or gravel but, you do need to take care with the kind of substrate that you use – the Molly fish will often eat substrate and, if this is too sharp, it can cut the fish’s mouth. For this reason, its best to use a soft, natural sand in your tank. 

As with many of us humans, the Molly Fish likes a plant in the habitat and often use these as hiding spaces. While these fish are pretty much good with any plant, ideal species are aquatic grasses such as Sagittaria. If you’re breeding your Molly Fish, you may want to add some more dense vegetation to give the female somewhere to hide out when she’s getting ready to give birth. 

Ideal temperature and pH

As we’ve mentioned, the Molly is pretty easy to look after, however, it does require clean water and living conditions as follows: 

  • Temperature: 22 – 25 centigrade
  • PH: 7.5 – 8.5
  • dGH: 15-30

Failure to provide adequate water conditions for your fish can lead to the potentially fatal ‘Molly Disease; something which is common with this species. 

Do Molly Fish need a bubbler?

Yep. Although oxygen is introduced to the tank from filtration bubbles, you’ll still need to invest in a bubbler (air pump or air stone) in order to sufficiently aerate your aquarium with breathable oxygen. 

What are the symptoms of Molly Disease ?

When afflicted with Molly Disease, your fish will begin to appear less active and will not be moving around the tank as much as normal. Your pet may also start to display some odd behaviour and movement, such as moving with a wriggling motion.  If you spot these symptoms with your Molly Fish, don’t panic as it can be rectified. Check the conditions of the water in the tank and make adjustments where necessary. In most cases, your fish will soon begin to recover once the conditions in the tank have been corrected. 

What other diseases do Molly Fish suffer from ?

Another common ailment with Mollies is Ich and, this usually presents as a change in daily habits as with Molly Disease as well as a change in appearance of the scales, for example a change in colour. As with Molly Disease, Ich is almost always caused by water conditions so check that all is OK and make changes where needed. 

The Molly Fish may also be afflicted by fin rot disease. This is caused by bacteria and fungus in the tank and will often present as white spots on the body and fins of the fish. 

Tank mates

Most people tend not to keep just one fish in a tank so, you may be wondering what kind of pals your Molly will get along with. Molly Fish are sociable creatures and, as well as being kept with other Mollies, they get along with other species of a similar size. Although the Molly is generally non-aggressive in nature, they don’t like to be crowded so make sure that you’re not putting too many fish in the tank – three or four is usually the sweet spot. You should also try to ensure that the majority of your fish are female in order to avoid rare but possible aggression. 


Feeding is, of course, a big part of taking care of your Mollies. Molly Fish are omnivores, which mean that their diet consists of both animal and plant foods. To keep your fish as healthy as possible, you’ll want to replicate their natural diet as closely as possible. You can feed your Molly Fish: 

  • Algae
  • Blanched lettuce and spinach
  • Bloodworms (live and frozen)
  • Shrimp (live and frozen)
  • Fish flakes
  • Fish pellets

While your Molly Fish will happily consume frozen invertebrates, they do like to scavenge so, it’s a good idea to introduce live shrimp and bloodworms on occasion. 

As tiny as Molly Fish are, you don’t need to give them a lot of food – to hit the sweet spot, try feeding twice a day with an amount of food which they will consume within two minutes. Getting the feeding routine may take a little trial and error but, the two minute system is a good rule of thumb to start off with. 

Are Molly Fish tank cleaners ?

Yes – as Molly Fish eat algae, they will help to keep their tank clean, however, as we’ve said, you do need to make sure that the water in the tank is super clean at all times in order to prevent diseases such as Molly Disease and Ich. 

Can I breed Molly Fish ?

Yes you can ! The good news is that Molly Fish are pretty easy to breed as long as you follow a few golden rules: 

The Molly Fish will reach sexual maturity at eight weeks of age and its unwise to attempt breeding before then (if you don’t want your fish to breed, you’ll want to separate males and females before they reach this age). 


The female Molly Fish will generally be attracted to the largest male in the tank and, so, you’ll want to identify a healthy female and the largest male and place them together in a tank with clean water at a temperature of around 78 fahrenheit. It’s important to separate your breeding couple from other fish as, although the Molly is, in general, a peaceful creature, males will often fight over a female when it comes to mating. 

The dating game

The male Molly will usually begin to chase the female around the tank in preparation for mating. In some cases, the female will consent immediately by moving close to the male. If, however, she does not do this within two days then you can take that as a sign that she’s just not that into him – at which point, it’s a good idea to remove the male and replace with another – and repeat the process until the female finds the guy who’s just her type. 

The mating game

During the breeding process, the male Molly will fertilise the female by inserting milt (fish semen) into the female from his anal fin (gonopodium). Mollie are easy breeders and, so, nine times out of ten, the breeding process will be successful. 

The pregnancy

The Molly Fish pregnancy will usually last for around 45 days but, you will need to keep an eye on the mother to be from around 35 days to watch for any tell tale signs that she’s getting ready to give birth. These fish are livebearers so the female will nurture the eggs within her body and, then, give birth to live fry (baby fish). When the birth is imminent, the female will usually choose to find a dark and hidden area of the tank to do the deed. 

The birth

The female Molly Fish can birth up to 100 fry at a time and, the survival rate will usually be around 50%. Be sure to quickly remove the dead fry from the tank as soon as you can to avoid contaminating the water. 

Taking care of baby

Once the fry have been born, you’ll need to immediately remove the proud parents from the tank to prevent them from eating their young. You can then begin to feed the fry using fish flakes. You should continue this diet until the fry are around two months old, at which point, you can switch them to the same diet as your mature Mollies. As before, up to three fish can be kept in a 10 gallon tank but, any more than that, and you’ll need to upgrade. 

Final thoughts

While all of this might seem like a lot to take in, its a small price to pay for keeping your Mollies healthy and, being able to watch these delightful fish. Of all the most important parts of the Molly’s care, keeping the water clean and making sure that you don’t overcrowd the tank are both paramount. 

Molly Fish will usually cost between £2 and £5 and, you should beware if you come across somebody selling them for less. Although Mollies are available online, your best bet is to find a reputable dealer or tropical fish shop in your local area to make sure that you’re getting good, healthy fish. 

As long as you follow the simple rules in this article, your Mollies will thrive, even if you’re an absolute beginner.