How Many Swordtails in a 20-Gallon Tank?

Swordtails make excellent pets. They’re mild-tempered, low-maintenance, and pretty to look at.

If you just brought a small-ish tank, you might be wondering how many swordtails in a 20-gallon tank create a balanced ecosystem.

You can fit 4 or 5 swordtails comfortably in 20 gallons of freshwater, but you might be able to push it to 6 if they’re on the smaller side.

However, they are relatively large livebearers. The situation could get messy very quickly if you don’t prepare well.

Let’s find out how you can cut down the hassle in your 20-gallon swordtail tank!

How Many Swordtails in a 20-Gallon Tank?

They might not look like it, but an adult swordtail might grow to five or even six inches long.

If you follow the rule of thumb and allocate a gallon for every inch of fish, you might think that it’s okay to fit four swordtails in a 20-gallon aquarium.

However, this doesn’t hold up when you consider the amount of roaming space that will be lost to filtration systems, heavy plants, hiding spots, and even ground substrate.

Ideally, you should start with 10-15 gallons for the very first swordtail. Every extra fish needs five more gallons of water.

That’s two or three for your 20-gallon tank.

Meanwhile, the minimum recommended tank size for a group of 4-5 swordtails is at least 29 gallons.

This way, you account for all the lost water capacity without letting any significant resources go to waste.

Red Swordtail Male

Tips for a 20-Gallon Swordtail Tank

Regardless of how many swordtails you decide are a perfect fit for your tank, it’s important to maintain a balanced environment.

Here are a few tips that can help you make the most out of your 20-gallon swordtail tank:

Avoid Raising a Solitary Fish

While the 20-gallon tank is more than enough for a single swordtail, it might not be the best way to go at it.

Swordtails are community fish who need companions. Plus, you’ve got a healthy amount of roaming space in the tank, anyway.

You can either go for other swordtails or different species altogether. After all, they’re reasonably tempered and get along just fine with platies, mollies, and cherry shrimp.

Be careful, though. Both platies and swordtails are Xiphophorus, and they might crossbreed.

However, if you choose other swordtails, you’ll have to deal with their gender balance.

Balance the Male-Female Ratio

As a general rule, for every group of four, you need to have three females and one male. This should keep the pestering and territorial fights to a minimum.

Swordtails thrive better in groups of 3-5 fish, as long as the aquarium is well equipped to handle them.

Since you’ll only be able to keep two in your 20-gallon tank, you might be wondering how to balance the genders here?

It’s better to raise only two females because one dominant male could chase and pester the weaker fish.

Unfortunately, many stores sell swordtails as a trib. This means that they’ll only give you a pair of one male and one female.

To overcome this, you can see if you have any friends who keep swordtails and ask for two females from their upcoming fry batch.

Freshwater aquarium fish. Xiphophorus. Red Swordtail. Bright orange color. Blurred dark background. Black spots.

Don’t Aim for Breeding

Swordtails are avid breeders, and they don’t really need much to fill up an entire aquarium with baby fry.

After all, a single female fish can get pregnant, give birth, and get pregnant again, all under two months!

However, if your end goal with the 20-gallon swordtail tank is to create a breeding program, you’ll definitely struggle.

The tanks will get overcrowded very quickly, and the pecking will get tedious. Strong adult males will often fight and even eat the weaker ones.

The least you could do to successfully breed swordtails is a 40-gallon tank with weekly water changes.

For a smaller aquarium, it’s better to keep your goals ornamental with a balance of two or three fish.

Prepare for the Fry Anyway

If you’re not raising fish for breeding, you might still have to deal with their pregnancies every once in a while.

Much like guppies, female swordtails are sperm hoarders. They can store sperm inside them for a whopping six months!

Plus, you might get an already-pregnant one from the pet supplier. So, even if you raise females only, it’s better to prepare in advance for dealing with the baby fry.

Ideally, you should separate adults and fry. The babies should be moved to a tank with heavy plantations and minimal waste to boost their chances of survival.

Make plans on whether you want to keep them or give them away. If you leave them in the adult tank, they’ll end up being eaten and pestered to death.

Choose to Over Filter

Besides aggression, one of the most serious issues with an overcrowded aquarium is inadequate filtration.

Debris from food remnants and fecal matter mix up with a build-up of ammonia and nitrate to create a toxic environment that stresses the fish out.

Stress nurtures aggression because the weakest of the bunch get even more lethargic. Meanwhile, the stronger ones grow more dominant and territorial.

In essence, it’s a vicious cycle of pecking that will wreck your fish population very quickly.

That’s why it’s recommended to over filter rather than risk your pets’ health. Hang-on-back systems usually work best here.

How Can You Tell Male and Female Swordtails Apart?

By now, you probably realized that the perfect fit for your 20-gallon tank is two medium-sized female swordtails or two females and one male if they’re all petite.

This begs the question: how can you differentiate between both genders?

The male swordtails have a characteristic tail fin extension that sets them apart from the females with a rounded tail fin. Plus, the females are usually chubbier.

So, take a long hard look before you commit to your new aquarium community!

The Takeaway

Figuring out how many swordtails in a 20-gallon tank keep the system balanced is all about understanding the breed’s needs.

Ideally, the 20-gallon tank will hold two or three fish only. However, females must always outnumber males to keep the aggression level down.

As always, you should be vigilant about your tank maintenance!

Have Another Tank Size You’re Looking for?

How Many Swordtails in a 5-Gallon Tank?

How Many Swordtails in a 10-Gallon Tank?

How Many Swordtails in a 29-Gallon Tank?