How Many Swordtails in a 5-Gallon Tank?

Figuring out how many swordtails in a 5-gallon tank make a decent balance can be a risky business.

While it’s not ideal, you can only keep one swordtail fish in a 5-gallon tank as long as it’s only a temporary solution.

This might be bad news for people who enjoy the convenience of smaller aquariums, but it’s all for good reason.

Let’s find out all about that!

How Many Swordtails in a 5-Gallon Tank?

If you want to keep swordtails, you need to start with at least 10-15 gallons for the very first fish. Ideally, each extra swordtail you add to the tank needs around 5-6 gallons of water on top of that base aquarium capacity.

In this sense, the good-old 5-gallon tank can be a way-too-small home for even one swordtail.


Why Is a 5-Gallon Tank Too Small for Swordtails?

On average, an adult swordtail ranges around 5.5 inches. Meanwhile, the typical 5-gallon aquarium is 16 x 8 x 10 inches.

If you have previous experience raising fish, you can tell why that’s not a good fit. It’s a sure-fire way to turn the playful species into aggressive, miserable, and unhealthy fish.

Here are a few reasons that make the 5-gallon tank too small for adult swordtails:

It Nurtures Aggressive Behavior

Although the degree of aggression is mostly related to each species’ temperament, it also has to do with the aquarium environment.

When fish are physically overcrowded, they tend to get very territorial over the available space, food, and mating partners.

That’s why keeping more than one swordtail in such a small tank will almost certainly lead to fighting within the group.

Things might get so bad that the dominant males end up splitting the weaker ones’ fins and causing visible wounds all over their bodies.

It Lacks Enough Oxygen Supply

Even if you only have a couple of swordtails, you’ll be putting them at risk of fatal oxygen deficiency.

Using an air pump can help improve the air circulation temporarily. However, in the long run, you’ll have to move the fish into a bigger tank.

Keep in mind that older fish are even more sensitive to the subtle changes in dissolved oxygen levels.

You’ll be able to tell that the fish are oxygen-deprived if they hover a lot over the filter. They can also become lethargic and swim off-balance.

It’s Not a Full 5-Gallon Capacity

When you buy a 5-gallon tank, you have to keep in mind that this is its capacity when it’s empty. That doesn’t take into consideration all the space that the equipment and decorations take over.

You’ll be keeping plants, hiding spots, pebbles, and filters in the small tank. These all take up vital swimming space from the fish.

So, in reality, you’re not even giving your pet the full five gallons of water. This makes the already-small aquarium all the more ill-suited for swordtails.

Can You Keep a Single Swordtail?

By now, we’ve established that the 5-gallon tank can hardly hold one swordtail comfortably. Yet, most domestic fish keepers would prefer an aquarium full of fish.

Since that’s not feasible, you might be wondering whether or not you can even raise one solitary swordtail?

It’s not impossible to keep a single swordtail happy and healthy, but in most cases, they’re better off in groups. Ideally, they need to exist with three or four tank mates to thrive.

After all, they’re a highly social and playful species!

It might sound so trivial to be bothered about a fish’s social needs. However, you can’t overlook the serious effects that loneliness can have on any conscious creature.

As it turns out, fish too can get anxiety from low serotonin levels when they’re kept in isolation.

Orange Swordtail

What Fish Can You Keep in a 5-Gallon Tank?

If you’ve decided against getting swordtails for your aquarium, you might want to consider smaller alternatives.

Here are a few dazzling fish types that can survive in a 5-gallon tank:


The average adult betta is around half a swordtail at 2.4-3.1 inches. Plus, they can handle isolation really well, making the 5-gallon tank ideal for a single betta fish.

While the majority of the pet betta population comes from captive breeding programs, their wild population is declining rapidly. So, be gentle with those tiny beauties!


Believe it or not, the adorable guppies are even smaller than the bettas. They range between 1-1.5 inches!

With only five gallons of freshwater, a decent tank filtration system, and minor maintenance, you can raise three or even four happy guppy fish.


Only a tiny bit larger than guppies, killifish is a strong candidate for any nano tank. Five gallons can be enough for a pair of those long-bodied charmers.

However, it would be better to avoid raising two males together because they can get a bit aggressive towards each other.


A regular platy fish can grow up to 2-3 inches tops. Meanwhile, a platy of the dwarf breed might never cross the one-inch mark.

If you consider the general recommendation of adding a gallon for every inch, you can keep a couple of platies in your 5-gallon tank.

Cherry Shrimp

Although they’re not very long-lived, many people like keeping decorative freshwater shrimp aquariums.

Besides being painstakingly cute, they’re so minuscule that you can fit up to 25 of those bad boys comfortably in a 5-gallon bucket.

The Takeaway

Although they’re wildly convenient, there isn’t much room in 5-gallon tanks.

When you’re trying to fit the relatively large swordtail in one of those nano aquariums, you might find yourself in a tight corner.

We get that it’s hard to figure out how many swordtails in a 5-gallon tank make a balanced ecosystem. To take the guesswork out of it, add a gallon for every inch of fish you have.

You could get away with using a smaller tank for temporarily transporting only one swordtail, but don’t push your luck further than that.

Swordtails need at least 10-15 gallons of roaming space. Otherwise, you risk the fish’s health.

If you’re looking for a better fit for your 5-gallon tank, you might want to consider smaller alternatives like guppies or cherry shrimp.

Have Another Tank Size You’re Looking for?

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