15 Small Freshwater Fish for Nano Aquariums (The Ultimate Guide)

If you enjoy keeping small fish then why not consider a nano aquarium for them? There are a lot more nano fish available in the hobby than you might expect. So which of these small fish are a good fit for your small tank?

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15 Awesome Small Freshwater Fish for Nano Tanks

Here are our top 15 pick for the best freshwater nano fish:

1. Betta Fish

As one of the most popular species in fish keeping, Bettas are prized for their vibrant colors and hardy nature. Bettas are capable of surviving in small tanks and are flexible when it comes to water conditions. Making them a great choice for beginners.

Despite what you may read online (or even hear from pet store employees), Bettas should never be kept in small cups or bowls. Large pet store chains  tell new aquarists this as a “marketing gimmick” to sell more Betta fish.

In reality, Bettas should be kept in tanks of at least 5 gallons with a functioning heater and filter.

• Minimum Tank Size: 5 Gallons
• Size: 3″
• Care Level: Easy
• Temperament: Peaceful to Semi-Aggressive

2. Dwarf Puffer

Contrary to popular belief, Puffers are not only a saltwater species. Several types of Dwarf Puffers are native to freshwater environments and thrive in nano aquariums.

Pea Puffers only grow to about an inch in length. A half doze will fit comfortably in a 5 gallon aquarium. But if you want to keep your pea puffers with other fish, you’ll need to provide extra space.

These small freshwater fish are aggressive. They love nipping the fins of their tank mates. Pea puffers also chase each other all of the time.

Pea Puffers do best in aquariums with plenty of live plants and hiding places. They are very curious, so be sure to give them plenty of entertainment in the form of vegetation and driftwood.

Puffers are a carnivorous species, so they require a steady supply of meaty foods. You should also offer live snails. The shells will keep the sharp teeth of these small fish worn down.

• Minimum Tank Size: 5 Gallons
• Size: 1″
• Care Level: Moderate
• Temperament: Aggressive

3. Celestial Pearl Danios

Danios come in all shapes and sizes – and the Celestial Pearl Danio is among the tiniest of the group. This small freshwater fish has stunning colors and is interesting to watch. Making it a favorite among nano aquarium owners.

Since Celestial Pearl Danios (also known as CPDs) are schooling fish, we recommend keeping them in groups of 4-6. Groups are fine in tanks as small as 5 gallons, though 10 gallons is recommended if possible. That way, you can keep more Celestial Pearl Danios together.

These tiny fish are omnivores, so they do best with a mixture of plant-based and meat-based foods. That said, they aren’t picky eaters and enjoy flake foods, algae wafers, brine shrimp, and freeze dried blood worms.

• Minimum Tank Size: 5 Gallons
• Size: 1″
• Care Level: Easy
• Temperament: Peaceful

4. Bumblebee Goby

Bumblebee Gobies are one of the most unique species on our list of small aquarium fish. For one, they can be kept in both freshwater and brackish tanks. These small pet fish only get to around 1.5 inches, but have bold personalities.

They will act territorial toward others of the same species. So provide plenty of hiding spaces when housing more than one Bumblebee Goby in the same aquarium.

Unlike most of the other species of our list, Bumblebee Gobies are not the most ferocious eaters. In community aquariums, they are often outcompeted for food because they eat rather slow. If you keep these Gobies with other fish, watch during feedings to make sure they’re getting enough food.

• Minimum Tank Size: 5 Gallons
• Size: 1″
• Care Level: Moderate
• Temperament: Peaceful; Territorial

5. Sparkling Gourami

Sparkling Gourami, also known as Pygmy Gourami, are small fish in the Gourami family. These freshwater aquarium fish are prized for their bright, iridescent colors. Sparkling Gouramis do best in small groups, so purchasing 3 or more fish is recommended.

These tiny fish are native to habitats with tons of natural foliage. So they tend to be happiest in tanks with lots of plants and driftwood. In addition to providing tons of hiding places, plants will enhance the colors of these cute little fish.

Pygmy Gouramis are an omnivorous species and do best on a mixed diet of plant-based and meat-based foods. Flakes mixed with a pinch of bloodworms are all they need for longevity and possible breeding.

• Minimum Tank Size: 5-10 Gallons
• Size: 1″
• Care Level: Easy
• Temperament: Peaceful

6. Endler’s Livebearers

The Endler’s Livebearer is a small freshwater fish known for its bright, psychedelic patterns. Much like other livebearers, Endlers will breed with ease. So be prepared for some baby fish if you plan to keep this species.

In addition to their awesome colors and breeding tendencies, Endler’s Livebearers are small fish for community tanks. They thrive in different water conditions. Which makes them a great choice for beginner or low maintenance tanks.

Like  most of the small species of fish on our list, Endler’s Livebearers are omnivorous. A simple mix diet of flake food and the occasional meaty snack will work well.

• Minimum Tank Size: 5-10 Gallons
• Size: 1″
• Care Level: Easy
• Temperament: Peaceful

7. Least Killifish

The Least Killifish is a small freshwater fish found all over the Southeastern United States. Closely related to Guppies and Mollies, Least Killifish are not true Killifish.

Instead of laying eggs, they give birth to live young. And as livebearers, they will breed often in home aquariums.

Least Killifish grow to about 1.5″ long. Making them great fish for small aquarium sizes. They are forgiving when it comes to water conditions and adjust well even to sudden changes in parameters.

• Minimum Tank Size: 3 Gallons
• Size: 1.5″
• Care Level: Easy
• Temperament: Peaceful

8. Norman’s Lampeye Killifish

The Norman’s Lampeye Killifish is one of the best fish for small tank keepers. Lampeye killifish get their name from the glowing patch on top of each eye. Like the stripe of a neon tetra, it allows the small fish school to coordinate their movements.

Lampeye Killifish prefer to be kept in groups of 3-5 fish in a tank. Since they stay pretty small (usually around 1.5″ at max length), a small group can easily be kept in tanks as small as 5-10 gallons.

Lampeyes do best in aquariums with plenty of live plants. So they make a great choice for those looking to set up a planted tank.

• Minimum Tank Size: 5-10 Gallons
• Size: 1.5″
• Care Level: Easy
• Temperament: Peaceful

9. Crystal Red Shrimp

Yes, Crystal Red Shrimp aren’t fish. But they make great nano aquarium inhabitants nonetheless. These tiny freshwater shrimp are beautiful and somewhat easy to keep.

They aren’t as tough as Red Cherry Shrimp (see below). But Crystal Reds are in the realm of beginner pets. Plus they will thrive in tanks as small as 3-5 gallons.

Crystal Reds tend to end up as snacks if larger fish are present. If you want to keep shrimp, you should either stick with a shrimp-only tank. Or keep them with any of the nano fish on this list. Except pea puffers, which enjoy eating shrimp.

Crystal Red Shrimp do best in aquariums with plenty of live plants and driftwood. In the right environment, CRS are known to reproduce fast. That said, a 5 gallon aquarium is capable of supporting a large colony.

• Minimum Tank Size: 5 Gallons
• Size: 1″
• Care Level: Moderate
• Temperament: Peaceful

10. Red Cherry Shrimp

If you like the idea of setting up a shrimp tank, Red Cherry Shrimp are probably the easiest species you can pick. These little guys are pretty forgiving when it comes to water conditions (more so than Crystal Reds) and reproduce extremely quickly.

As with any type of dwarf shrimp, Red Cherry Shrimp will get along with small fishes. Don’t choose species much larger or they will be eaten. RCS are also entertaining on their own and display beautiful contrast against green plants. As with Crystal Reds, Cherry Shrimp prefer planted tanks with lots of hiding spots.

• Minimum Tank Size: 5 Gallons
• Size: 1″
• Care Level: Easy
• Temperament: Peaceful

11. Chili Rasbora

Chili Rasboras aren’t just nano fish. They are one of the smallest fish in the world. These little cyprinids are related to barbs, danios, and goldfish. There are a few fish sold under this name, with somewhat different patterns of black spots. But all have the same care needs.

The one thing that Chili Rasboras do need is soft to neutral water parameters (pH 4.0-7.0) They do well even in blackwater environments with strong acid chemistry. You also need to find food small enough for them. Daphnia and baby brine shrimp are their favorite prey items.

Last, choose tank mates their size or a little bigger. Even other small freshwater fish might give them trouble. A full grown Betta Fish could eat a Chili Rasbora. But freshwater shrimp and Endler’s livebearers are all the same size as them.

• Minimum Tank Size: 5 Gallons
• Size: ¾” 
• Care Level: Easy
• Temperament: Peaceful; Schooling

12. Scarlet Badis

The Scarlet Badis (Dario dario) is an underappreciated small aquarium fish. They are long lived for such tiny fish; 4 to 6 years is normal for them. In pet stores they look rather sad and drab since they are too stressed to show their true colors.

But bring some home and put them in a planted tank with low lighting and plenty of cover. The males turn an intense scarlet color to impress females. The one downside is that Scarlet Badis are very territorial. 

You can keep males together but you need 10 gallons of space per male Badis. In a nano tank, you should keep just one male, with one or two female fish.

• Minimum Tank Size: 5 Gallons
• Size: ¾” 
• Care Level: Easy
• Temperament: Semi-aggressive; Territorial

13. Pygmy Sunfish

If you like North American native fish, the Pygmy Sunfish is one of my favorites. They are from the genus Elassoma. Several, such as the Everglades Pygmy Sunfish (Elassoma evergladei) are colorful, with blue spangles and a deep black color to the males.

Pygmy sunfish are good small freshwater fish for unheated coldwater tanks with plants that prefer the same temperatures. North American invertebrates like ghost shrimp and snails make good tank mates for them.

 As carnivores they need blood worms, brine shrimp, and other meaty foods. Weaning them onto flake and pellet foods may be impossible if they are wild caught. Sometimes you will find captive bred fish, however. These eat prepared foods with relish.

• Minimum Tank Size: 5 Gallons
• Size: 1″ 
• Care Level: Easy
• Temperament: Peaceful

14. Ember Tetra

Tetras are a step up from some of the other small fish on this list. They are a bit more sensitive to nitrogenous waste. Plus they need more swimming space. I recommend people start out with 20 gallons for tetra fish.

Except for the ember tetra. A full grown specimen is just ¾ inch long, so a school is comfortable in 10 gallons of space.

These tiny fish do well with other community fish their own size. Chili Rasboras, Least Killifish, and freshwater shrimp enjoy the same water parameters they do. Ember tetras may even spawn for you if kept in a planted tank with lush growth.

• Minimum Tank Size: 10 Gallons
• Size: ¾” 
• Care Level: Moderate
• Temperament: Peaceful; Schooling

15. Dwarf Otocinclus

Plecostomus and other algae eating fish tend to be rather large. But there are small aquarium fish that do the job of eating algae that builds up in a nano tank. The best is the Dwarf Otocinclus.

As suckermouth catfish they are related to Plecostomus but they grow to be 1 inch long. Dwarf Otos are sociable fish that live in groups of thousands of small fish in the wild. So keep at least 3 together.

Planted tanks are where Dwarf Otocinclus do best. They will gently clean algae from plant leaves. And may even spawn for you. Feed them algae wafers, boiled vegetables, and other plant based foods if they run out of algae.

• Minimum Tank Size: 5 Gallons
• Size: 1″ 
• Care Level: Easy
• Temperament: Peaceful

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Setting Up A Nano Aquarium

Now that we’ve discussed nano fish for small tanks, let me show you how to set the aquarium up the right way.

Choosing a Tank

Picking out your nano tank is the first major milestone. I like to go with all-in-one options. Here are a few of my favorite picks:

Fluval Spec V – Best 5 Gallon Nano Tank

The Fluval Spec V is well-known as one of the best nano aquariums on the market for small fish. This 5 gallon all-in-one tank comes stocked with just about all the equipment you need to get started.

It includes a built-in filtration system and an LED light powerful enough for low to medium light live plants. The light provides full spectrum output as well, which is important for photosynthesis.

In addition, the sleek look of this unit makes it a good choice for most interior decor designs. No matter what type of small fish or shrimp you plan to keep, the Fluval Spec V is hard to beat.

Marineland Contour – Best 3 Gallon Nano Tank

If you’re looking for something a little smaller than the 5 gallon Fluval Spec V, the Marineland Contour is your best best. The curved, one-piece glass construction gives the Contour a classy look that a lot of nano aquarium owners look. In addition, the small footprint of this tank allows you to place it anywhere. It’s great for your desk, office, or bedroom.

Filtration

A common misconception about nano aquariums is that they don’t need filters. People look at small tanks and think, “How much waste can these tiny fish really produce?”.  In reality, nano tanks actually need filtration units more than larger tanks. Because the water parameters will shift faster and easier in such a small volume of water.

If you decided to go with something other than the all-in-one options above, you’re going to need a filtration unit. I recommend the Deep Blue Professional Nano Filter for tanks 5 gallons and under. It is powerful enough to offer great filtration. Yet low profile enough to keep your tank looking sleek.

Cycling Your Aquarium

Cycling an aquarium is the process of building up colonies of beneficial bacteria that convert harmful fish waste into safer compounds. Without cycling your aquarium, ammonia and nitrite levels will rise. Causing fish stress and soon killing them.

I discuss the cycling process in much greater detail in my aquarium cycling guide here.

Live Plants and Aquascaping

Live plants are a great way to create a natural environment for your fish. In fact, plants actually help make your tank healthier by removing toxins (such as ammonia and nitrite) from the water. But how do you get started with live plants? Here are a few species that are easy to keep, hardy enough for beginners, and do well in nano tanks:

• Java Moss
• Java Fern
• Anubias Nana
• Marimo Moss balls
• Duckweed
• Crypt. Wendtii
• Micro Swords

In order to keep your plants healthy, you’re going to need a planted aquarium light. Once again, you have a slight advantage if you decided to go with one of the all-in-one units above. They come with LED fixtures that will sustain most low light plants.

If you are setting up a tank from scratch and want to keep live plants, I suggest the NICREW Classic LED. It’s a great beginner light that will remain relevant if you decide to keep more advanced plant species.

Additional Reading: If you’re serious about keeping live plants, check out our complete step-by-step guide to setting up a planted aquarium.

Maintenance

Many people believe that nano aquariums are easier to keep than larger aquariums, but this couldn’t be further from the truth. Since nano aquariums have such small water volume, they are susceptible to large parameter fluctuations (even from slight changes). A faulty heater can cook your fish in a matter of minutes, whereas a larger tank would take hours to heat up.

As a result, it is important to keep up with water changes and testing. I recommend weekly water changes if possible. Make sure you only add dechlorinated water to your tank (since you definitely don’t want to poison your fish).

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Conclusion

A 5 gallon setup can be just as beautiful and enjoyable as a 50 gallon setup. Especially with the amount of small freshwater fish species out there. A nano tank with small fish is faster to maintain and easier to find a place for in any home or office space

Just avoid overstocking your tank, feed sparingly, and keep up with regular water changes. With the small freshwater fish, shrimp, and plant suggestions on this list, your tank will be cycled and flourishing in no time.