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How Many Fish Can Be in a 3 Gallon Tank? – Recommend Fishes for Your Tank

how many fish can be in a 3 gallon tank

How many fish can be in a 3 gallon tank? A 3-gallon fish tank may hold three 1-inch fish if the standard rule of 1 inch of fish per gallon of water is applied. You can keep 2-inch fish with an invertebrate companion, such as a cherry shrimp or a nerite snail.

A standard 3-gallon fish tank size is roughly 12″ x 6″ x 8″. The capacity of a nano tank decreases as you add equipment, so you need to keep that in mind as well.


Table of Contents

List of Fishes That Can Live in a 3-gallon Tank

What fish can live in a 3-gallon tank? Here are a few:

1. Guppies


Size 1.2-2 inches
Care Level Easy
Diet Omnivorous
Temperature 72-82°F
Temperament Easygoing
Number of Guppies you can keep in a 3-gallon tank 2-3

One of the most popular fish that can live in a 3 gallon tank, guppies are a favorite choice among both beginners and experts. They are easy to take care of and are very friendly pets to have.

A guppy is ideal for a 3-gallon aquarium for its size. Guppies range in size from 0.6 to 1.4 inches in length for males and 1.2 to 2 inches for females.

2. Betta Fish


Size 2.25 inches
Care Level Easy
Diet Carnivorous
Temperature 75-80°F
Temperament Semi-aggressive
Number of Bettas you can keep in a 3-gallon tank  1

An adorable type of fish for a 3-gallon tank, Betta fish are well-loved for their colorful fins. They can make a fish tank lively with their vibrant appearance and ability to learn tricks (yes, they can swim through hoops!).

Also known as Siamese fighting fish, Betta fish can be aggressive. While some of them are simply calm or energetic, there are highly territorial ones especially among males. You can have only one betta fish in a 3-gallon tank.

4. Neon Tetras


Size 1.2 inches
Care Level Easy
Diet Omnivorous
Temperature 70-81°F
Temperament Calm
Number of Tetras you can keep in a 3-gallon tank 1-2

Neon tetras are freshwater fish, which despite their reputation as schooling fish, feel secure when roaming in mere groups of three.

Neon Tetras in a 3 gallon tank filled with plants look amazing! Their neon colors stand out against a rich green backdrop. If you use a black light, neon tetras’ skin seems to glow in the dark.

5. Least Killifish


Size 1.2 inches
Care Level Easy
Diet Omnivorous
Temperature 68-78°F
Temperament Calm
Number of Least Killifish you can keep in a 3-gallon tank 3

Heterandria Formosa, aka Least Killifish, is the smallest known species of livebearer fish and one of the tiniest fish species in the entire world. They are not often found for sale, but they are generally accessible within hobbyist groups.

As they are not picky eaters and will take most food given to them, killifish are the least demanding nano fish.

6. Chili Rasbora


Size 0.7 inches
Care Level Easy
Diet Omnivorous
Temperature 68-82°F
Temperament Calm
Number of Chili Rasbora you can keep in a 3-gallon tank 5-6

Though less well-known than Guppy, Chili Rasbora makes a great addition to a three-gallon tank. Due to their peaceful temperament and easy maintenance needs, this fish species is slowly getting popular.

As far as aquatic creatures go, Chili Rasbora is one of the tiniest. A minimum of six fish can be housed together-and should be-since they shoal (stay together for social reasons).

Chili Rasbora have a variety of hues, so keeping them together will make your tank attractive. They are also very active and playful!

7. Zebra Danios


Size 2 inches
Care Level Easy
Diet Omnivorous
Temperature 64-75°F
Temperament Calm
Number of Zebra Danios you can keep in a 3-gallon tank 4

 If you’re looking for a hardy fish for your 3-gallon tank, Zebra Danios is perfect for you. It requires minimal care and can thrive in a nano tank with proper attention.

This type of fish will consume almost everything you give them. They can feed on Aqueon tropical flakes, worms, shrimp pellets, etc.

Factors Affecting the Number of Fish in a 3-gallon Tank

Aside from the size of fish you plan on keeping, equipment and space plays an important role in determining the number of fish you can fit in your 3-gallon tank. Live plants, filters, lighting, decorations, and surface area all matter.

More fish means higher oxygen exchange rates, so larger water surface areas are necessary. Even while a tall, thin tank and a short wide tank can both store the same amount of liquid, their surface areas are very different.

Lastly, the number of fish that can be kept in a tank depends heavily on filtration. A filter must have a flow rate of at least six times the fish tank’s capacity.


What Fish You Should Not Keep In A 3 Gallon Tank?

Very active nano fish that show schooling behavior, such as barbs, platies, and pygmy cory catfish, shouldn’t be housed in a 3-gallon tank. They require not just a huge open swimming area but also need to be kept in groups of at least six to eight.

Fish that are aggressive with other species like pea puffers (dwarf pufferfish) are not ideal for nano tanks–they may also fight other pea puffers when crammed together.

Make sure not to have fish and invertebrates that may fight or prey on each other.

You also can’t keep a pet goldfish in a 3-gallon tank because it can grow up to a maximum size of 2 to 3 inches, and by the time they are completely grown, it can measure up to 6 to 14 inches.

How Often Should You Change The Water In A 3-Gallon Tank?

A weekly water refill for a small tank is essential. You must change 10 to 15 percent of the water each week.

How Many Fish Can Fit In A 3.5 Gallon Tank?

The maximum fish length for a 3.5-gallon tank is 3.7 inches. 3.5 gallons can accommodate a large number of vibrant little shrimp in freshwater tanks. Additionally, certain small shrimp and corals are available for saltwater aquariums.


If you follow the general rule of “1 inch of fish per gallon of water”, a 3-gallon fish tank can hold three 1-inch fish or a 2-inch fish with an invertebrate companion. However, you also need to consider the dimensions of your tank and the stuff you’ll put in there.

Some of the best fish for a 3-gallon tank are guppies, betta, neon tetras, least killifish, chili rasbora, and zebra danios. Species like guppies and zebra danios are perfect for beginners as they are very low-maintenance.

Now you know what to consider for your 3-Gallon Fish Tank Stocking Ideas!

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