Molly Fish Species Overview
Mollies are ubiquitous in the world of fish keeping, and with a huge array of varieties and colors, they remain a stalwart in most aquariums with good reason.
These freshwater fish are easily recognizable to most people, including those who are not hobbyists. They make perfect starter fish for beginners with a reputation as easy to care for, feed, and even breed.
Their peaceful temperament makes them especially ideal as tank mates, and their hardy nature makes them less problematic than most species.
Native to freshwater streams and rivers of North and South America, Molly fish have a variety of habitats but typically like sandy beds with rocks and places to hide.
Let’s take a look at what makes Mollies so popular.
Mollies Behavior
Mollies are calm, peaceful mid-tank swimmers who often form a group and enjoy schooling.
They prefer company and fare better in a group rather than on their own. It’s advisable to have a high proportion of females with perhaps a few males as the males can harass them and are known to stress them out.
They are highly social and active little fish which means hobbyists can often get quite attached to their perky personalities. And personality is something most Mollies have quite a lot of!
They are fascinating to watch and create a real hive of activity to a tank. Personalities are often quite apparent to the casual observer quite quickly, which is probably another reason they are so well-liked by fish keepers across the board.
Mollies are livebearers, so their eggs develop internally, and they give birth to live fry, which can be exciting to observe.
Molly Fish Lifespan
A healthy and well cared for Molly can be expected to live up to 5 years.
Something to consider beforehand is if you plan on breeding them. They can breed often and will usually eat their fry. Some keepers allow the fry to be eaten, but if you don’t, you’ll need to either separate the adults using a breeding box or a separate tank altogether.
And you’ll need to work out what to do with so many new Mollies!
Mollies Appearance
This is where Mollies really come into their own for beginner fish keepers. As a hardy species, you really can’t argue that their lively nature and the vast array of colors make them pretty hard to beat as starter fish.
Generally, females can grow up to 4.5 inches, and males will be smaller and get up to 3.5 inches in length.
They are tallest in their middle section and taper to a tip at the nose. They are generally quite flat and have a large caudal fantail.
Their dorsal fins can lay flat or be raised up at various times.
We will make a note here about a type of Molly known as Balloon Mollies. These are a somewhat controversial variety that has been bred to have a round balloon-shaped abdomen which is formed by this variety have a rounded curvature of their spine.
While this may look interesting, this selective breeding for the trait results in compression to their internal organs and can cause problems with digestion. The health issues these fish have means that anecdotally they have a shorter lifespan.
Moving on, here is the coloration of some popular varieties that you might spot in aquariums on a regular basis:
- Common Molly – dull silvery body with some black dots and yellowy tips to their dorsal and caudal fins
- Black Molly – the entire fish is black
- Sailfin Molly – the dorsal fin is much taller and starts close to the head and covers most of their back, appear in a variety of colors
- Lyretail Molly – the caudal fin is much larger, and the top and bottom ends form points that trail behind the fish, which looks quite showy
Popular colors include white, black, golden, platinum, dalmation, creamsicle, red, and many, many more!
Molly Fish Habitat And Tank Requirements
Mollies prefer slow-moving currents and water, so no special filters are needed, and they also do not need any special lighting; standard lighting is perfectly suitable.
In the wild, they have adapted to freshwater, brackish (slightly saline), and even some cases of saline habitats. However, they are predominantly freshwater in the wild. Most imported Mollies bred for fish keeping come from Asia, and they are raised in brackish water, which is found naturally and is, therefore, cheaper to maintain.
If you plan on having exclusively freshwater Mollies, you may need to source some local suppliers who have raised them that way as it isn’t ideal to transfer fish used to slightly saline conditions straight into freshwater.
They like sandy or light gravel substrates and generous plant life and water that is slightly alkaline.
Let’s take a look at what tank conditions are needed for having happy Mollies.
Tank Conditions
As mentioned before, you’ll want to line the tank with a sandy substrate or very fine gravel. Both are helpful for keeping live plants growing which provide them with hides.
Being tropical fish, they like warm water, which is kept at a steady temperature. Nitrates need to be kept low as they are sensitive to them and may cause issues if not dealt with quickly and appropriately.
Parameters should be kept within these guidelines:
- Temperature: 75-80º F (24-26.7ºC)
- Nitrate: <30ppm
- pH: 7.5-8.5
- GH: 12-25 dGH (200-450 ppm)
Mollies like and thrive in hard water as in the wild they are found in areas of high mineral content. If you have soft water, minerals will need to be added, like crushed coral which will leach calcium and carbonate into the water slowly.
In terms of salinity, it’s best to ask your supplier and follow their advice. Since most are imported, chances are you will need to add some salt to provide the brackish conditions most are reared in.
You must have a heater to create a steady temperature with little fluctuation.
Filtration is a major component of keeping Mollies happy. They are voracious eaters who never seem to stop searching for food. Coupled with the fact that you usually need a gang of them to provide adequate social interaction and that they breed frequently, they create a whole lot of waste.
As we know, fish tanks have a Nitrogen Cycle. All of the fish waste breaks down, and a byproduct of this breakdown is ammonia, which is highly toxic.
This is where beneficial bacteria step in from your chosen filter and convert all of that ammonia into nitrites. Nitrites, too, are toxic! The cycle doesn’t end there. A second type of good bacteria converts nitrites into nitrates.
Nitrates are substantially less toxic and can build up in the tank between water changes. The frequency with which your tank needs a water change is largely dependent on the sensitivity of your community to nitrates and how quickly they build up. Monitoring these levels is therefore critical to keeping your Molly population happy and healthy.
Extra filters can help as well as having a large enough filter to supply the beneficial bacteria to begin with.
Air stones can be a nice addition to provide extra airflow.
You’ll also want to avoid sharp edges in any added decor if you plan on having Sailfin Mollies as their fins are delicate can tear easily.
Tank Size
A single Molly needs a minimum of 10 gallons (38 L), but this size could support up to 4 if they are a smaller variety. Every additional Molly after that needs another 3 gallons (11.5L).
Choosing Tank Mates For Mollies
Knowing that a single Molly is a lonely Molly, you should be prepared to keep them company with their own species at a bare minimum. Keep the ratio of males low as they are always pestering the females to breed. And with enough females, the harassment can be spread around, so no one female ends up stressed by his ardor.
As Mollies are peaceful most of the time, they get along well with many other species, but the size of these tank mates needs to be carefully considered as Mollies tend to get a lot bigger and eat so much.
Your tank mates need to be able to hold their own when sourcing food and not be outcompeted by the Mollies whose appetites appear endless.
Choosing fish or crustaceans that occupy other levels of the aquarium can help with this, remembering that Mollies are highly active and tend to occupy mid-levels in the tank.
Excellent tank mates for Mollies include:
- Swordtails
- Platies
- Corydoras catfish
- Clown and Bristlenose Places
- Cherry Barbs
- Tetras
- Dwarf Gourami
- Zebra Loaches
- Angelfish
- Snails and Shrimp
Ones to avoid are anything overly large or with aggressive dispositions.
Molly Fish Health Issues
For the most part, Mollies are quite hardy, but like all fish, they can be susceptible to bacterial infections and have sensitivity issues.
Molly Disease
Technically this isn’t a disease at all, but it is a condition that you need to keep an eye out for.
When water condition is poor, you Mollies will be far less active and more sedentary, which is definitely not their nature! If they wiggle or shimmy on the spot, you probably haven’t been checking your water conditions frequently enough.
If you know water conditions aren’t quite right, you need to change the water straight away without delay, or your population is at risk.
Other Diseases
Ich and velvet are other common freshwater fish diseases that apply to Mollies too.
Common symptoms that one should look out for are a lack of appetite (a definite warning sign as we know how much Mollies love to pig out at all times of the day!), inactivity, spots or ulcers, and color changes.
The easiest way to have healthy, happy Mollies is to keep the tank meticulously clean with excellent filtration and test, test, test that water!
One last point to mention is that Mollies can also be susceptible to swim bladder disorders, which isn’t helped by their tendencies to gobble food all the time. If you spot abnormal swimming patterns and bloated abdomens, then it probably has an issue.
Interestingly, feeding thawed-out frozen peas has been shown to help improve the condition, so it might be worth a try to see if you can manage the condition if diagnosed.
How To Breed Mollies
For the beginner or Molly enthusiast, a better question might be how to stop them from breeding!
Joking aside, if you have one male in the group, then it’s not a case ‘if but when’ fry will arrive. This species is part of a group of fish who are livebearers. So this means that eggs develop inside their bodies, and fry emerge live when they are fully developed and ready for release.
They don’t need much encouragement to reproduce, but if you are trying to increase your chances of breeding sooner, a slight elevation in temperature can help get things moving, just like many other species.
Males perform a courtship display, and if a female is receptive to his advances, she will allow him to fertilize her eggs.
Anywhere from 35-45 days later, the live fry will be released. Depending on the variety you have, the number released will be from 20 on the low end of the scale and up to 100 for the largest Molly species.
As we mentioned earlier, the adults will happily eat the fry, so fry need places to hide in that all-important vegetation, or you need to separate them with a breeding box or a separate tank setup.
As strange as this may sound, it’s probably a good thing that the adults do often consume their fry as you could otherwise very quickly have an unmanageable population on your hands and in the tank!
Conclusion
In general, there is a lot of great reasons to incorporate Mollies into your fish-keeping repertoire. They are ridiculously easy to breed and have the added bonus of livebearing as well as a great social scene that makes watching them rather captivating.
Their little personalities make them fish that most keepers get quite fond of, and you’ll find yourself quite entertained by their active behaviors and lively character.
