15 Smallest Freshwater Aquarium Fish for Nano Tanks

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It can be quite hard to find the right fish for your aquarium, especially if you have a nano tank. You have to find the right fish to fit your aquarium not just regarding the right size, but also not to disturb the tank’s ecosystem.

It can be quite a challenge to get everything right with your nano aquarium; you have to consider the temperature and there is a lot of maintenance required to keep it clean.

But if you can balance the ecosystem of a nano tank, it can be very pleasing for the eye. Choosing the right fish is one of the most important decisions when it comes to nano tanks.

There are actually many types of fish that you can choose from, so let us take a look at the top smallest freshwater aquarium fish for a nano tank.

1. Dwarf Pea Puffer


Dwarf Pea Puffer

Pea puffer fish, also known as the dwarf puffer fish is a freshwater fish that originates from India. They only grow to up to 2.5 cm, so they are a small type of fish that are ideal for smaller tanks –  they need at least a 40 cm swimming space, so it is advisable not to put more than one pea puffer into your nano tank.

They can live comfortably in a 5 gallon (20 liter) aquarium, but if you want to keep more puffers, it is better to have a larger tank – 15 gallon (50-60 liter) will do.

Pea puffers are very lively fish that are curious and they move a lot. They thrive in an aquarium with a lot of hiding places and greenery, so if you want to keep pea puffers I advise you to also get a lot of plants. Also, you have to know that these fish are carnivores, so they may prey on your snails. Make sure you feed them enough worms and insects to keep them satiated.

2. Sparkling Gourami


Sparkling Gourami (sourceCC BY-SA 4.0)

Sparkling gourami are the smallest fish in the gourami family. They are sometimes also called pygmy gourami. This name originates from the fish’s looks – they are very colorful and bright. It is a bit unique, so you don’t often see them in home aquariums.

Their size can vary from 2,5 cm to 4 cm, so they are similar to pea puffers; they require a tank that can contain at least 5 gallon (20 liter), preferably more to keep them more accommodated.

These bright little fish are more inclined to swim in groups, so make sure that you do not keep a sparkling gourami alone in the tank – 5 or 6 of them would be ideal. Just like the dwarf puffers, this type of fish is very lively and also prefers to live in a tank with a lot of vegetation and driftwood so that they can hide and swim around it.

They are omnivorous – they eat both plant-based and meat-based food, so they are not picky. They can eat flakes as well as worms.

3. Licorice Gourami


Licorice Gourami (source – CC BY-SA 4.0)

This type of gourami fish is even rarer than the sparkling gourami. You want to be very careful with licorice gourami when maintaining them. They can grow from 2cm to up to 5cm, similar to the sparkling gourami fish. So a 5 gallon (20 liter) tank is a minimum when keeping the licorice gourami.

These fish are very adaptable, as they have adapted to live in very poor conditions. They can live in waters with very low pH, ranging from all the way down to 4.5.

In terms of food, they prefer to eat live food, so you can buy some worms, fleas and live insects to feed the licorice gourami. Keeping the right maintenance with licorice gourami can be very rewarding, as they are not only very beautiful to look at, but also in the right conditions they can breed quickly. And when they are in the breeding state, they are at their most beautiful.

4. Bumblebee Goby


Bumblebee Goby (source – CC BY-SA 4.0)

The bumblebee goby is an interesting fish. It can live in both freshwater and brackish water, but they prefer the latter. But it will live in freshwater too.

These interesting-looking fish grow up to approximately 4 cm, so they can live in a 5 gallon (20 liter) tank, but the ideal tank size for this fish is a 40 liter tank.

You want to be very careful when putting these guys into your tank, as they can be very aggressive and territorial towards other fish. They tend to swim just above the surface.

But what makes the bumblebee goby interesting is their behavior. I advise you not to keep more than one bumblebee goby in your tank so as not to disrupt the other fish.

The diet of these fish is the most complicated aspect. They are carnivore, so you want to feed them live food like worms and fleas, but as they live near the bottom of the tank, they might not get enough food, so keep an eye out that they get enough.

5. Endler Guppy


Endler Guppy (source)

If you want to lively up your tank, the endler guppies are the best choice. Their body is very colorful and bright, but what makes them popular is the fact that they are also very peaceful. The endler guppies, also known as the endler livebearers, come from South America.

They are very tiny – their size ranges from 2 cm to 3.5 cm, so they would do well in a 5 gallon (20 liter) tank. These fish are very lively and they can also reproduce quite quickly, so you want to limit that by separating the male and female fish. It prefers swimming in the upper parts of the tank and also prefers a lot of greenery.

The endler guppies are fine with both plant-based and meat-based foods as well as flakes. They go well with other peaceful fish in your tank. There are plenty of reasons for you to get an endler guppy – they are peaceful, colorful, lively and don’t require that much maintenance.

6. Otocinclus Catfish


Otocinclus Catfish (source)

Just like the endler guppies, the otocinclus catfish are a very friendly species. They mix up very well with other fish in the tank, as they are very peaceful.

Not only that, but another reason to have them in your tank is that they are very clean and they love to clean the tank and the plants within it.

They are relatively low maintenance regarding the food, but you actually have to keep the water clean for them, because they are quite sensitive to water quality.

As I said, they are happy to eat algae and any bits left on your plants. In that way they are low maintenance. When fully grown, they can grow to 4-5 cm. Ideally, they are good for you if you have a 10 gallon (40 liter) tank.

Be sure to keep the water clean, filtered and for everything else the otocinclus catfish are very adaptable.

7. Pygmy Corydoras


Pygmy Corydoras (source)

Another small fish for your nano tank, they grow to about 3 cm in size. They are very friendly and peaceful, so they would make an excellent addition if you want to have more fish in your aquarium. As for the aquarium size, they require at least a 5 gallon (20 liter) tank.

They tend to swim in the upper and middle parts of the aquarium. With their silver body with black lines, they are very nice to look at and they can balance the colors of the aquarium, especially if you have many colorful fish in it.

They are also quite low maintenance, as they will eat just about anything that comes into the water; from flakes to live food, the pygmy corydoras are not picky. What you might want to be careful about is that you do not put too many aggressive fish with the pygmy corydoras, because they do not like to fight for food and are very peaceful. Other than that, they can be a very nice addition to your aquarium.

8. Scarlet Gem (Dario Dario)


Scarlet Gem (Dario Dario) (source – CC BY-SA 4.0)

These fish are one of the smallest fish in your tank. Their size is around 2 cm, but females tend to grow larger than males, to about 2.5 cm – they can live in a 5 gallon (20 liter) tank.

But do not be fooled by its size; they can be very aggressive towards other males. They have very bright colors and they look like rubies. They can last from 3-4 years.

But they are actually quite shy and easily scared, so they hide in vegetation and other props in the tank. They are easily intimidated by larger fish. They spend most of their time hidden or swimming in the middle and lower parts of the aquarium.

They are, however, somewhat picky when it comes to food. They are predators in the wild, so you want to replicate the environment in your aquarium – they will eat live food, such as worms, shrimp, but they will refuse to eat pellets.

9. Microdevario Kubotai


Microdevario Kubotai (source – CC BY-SA 4.0)

Originating from Thailand, this tiny fish can be a very nice addition to your aquarium. Green in color, they can add variety to your habitat. They like to live in an aquarium that resembles a river, with rocks and greenery, but they will do well in other setups too.

They are very small – from 1.5 cm to 2 cm. The kubotai fish prefer to swim in groups, so it is better if you get more of them – 5-10 will do. They are perfect for small tanks of 5 gallon (20 liter) or more.

In terms of food, they feed on invertebrates and algae, but also on zooplankton. They will also accept dried foods such as flakes, but they prefer small live fleas. Like some other fish on this list, the kubotai will spawn eggs if the conditions are right. Make sure that you clean the water frequently and also disable them to reproduce too much.

10. Pearl Danio (Celestichthys Margaritatus)


Pearl Danio (source – CC BY-SA 4.0)

This fish with an interesting name comes from Southeast Asia – namely from Myanmar and Thailand. It lives in permanently flooded grasslands in shallow water.

The margaritatus are very beautiful: their body is grey with red and yellow pigmentations.

Males display larger amount of red pigmentation. It is a very small fish that can grow to up to 2 cm, but I still would not recommend you to keep it in small tanks; a 40 liter tank is more appropriate for the margaritatus because of its combative nature.

The margaritatus will eat dried foods but I do not recommend you to feed it just that; it also eats a lot of live foods such as insects, algae and zooplankton. The species is actually quite a recent one; it was discovered only in 2006.

11. Boraras Brigittae

This swamp fish originally comes from southwestern Borneo. This species is also under threat due to rubber or palm oil plantations. They are adaptable, but they prefer more acidic environments – the pH of the water could be as low 4.

They also prefer more dim waters due to the vegetation. They are tiny fish that swim in groups. While they do grow to about 2cm in size, they can live in 5 gallon (20 liter) aquariums, but a larger one (10 gallon / 40 liter) is even better because they swim in groups and they take up more space.

Like many other smaller fish on this list, they prefer to live in a denser environment with plenty of vegetation and obstacles, and that also helps to make the water more dim, which the boraras brigittae prefer. They eat live foods – worms, small insects, crustaceans. If you feed them dry food they will eat it too, but you should not be feeding the boraras brigittae only that – make sure you keep some variety in their food.

12. Boraras Naevus

Boraras naevus are very similar to boraras brigittae. People often mix the two species up as they are quite similar on the outside – the difference between the two is in color: the naevus is more on the orange spectrum, while the brigittae is red with a longer black stripe across its body.

The naevus, though, originates from Thailand and it is also a swamp fish. They are similar in size to the brigittae, as they grow to 2 cm and they can live in a 5 gallon tank.

The naevus likes pH neutral water with plenty of vegetation and roots. To keep them happy, it is best to put them into the aquarium with 5 or 6 other boraras naevus. It is omnivorous – it eats everything from dry food to live food, such as shrimp or worms. You have to adjust the size of the food though – make sure you do not give them too much.

13. Lambchop Rasbora (Rasbora Espei)


Lambchop Rasbora (sourceCC BY-SA 4.0)

The rasbora espei live in karstic forest streams of Thailand with plenty of vegetation. They prefer slightly alkaline water or neutral (pH of 7-7.4). These fish can be 3 cm big, so they require a bigger tank.

A 60 x 30 cm tank is probably the best option for these fish, especially if you want to keep them in a group (which is advisable). But other than that, they are a very peaceful fish and they will get along with other fish in your tank.

In terms of maintenance and food, they prefer to have softer, sandy and dark substrate, as it imitates their natural habitat; but they are quite adaptable. This species is a predator – they feed on smaller insects and worms, especially bloodworms. They also eat dried food.

14. Rasbora Axelrodi Blue (Sundadanio Axelrodi)

These shiny little blue-tinted fish are one of the most beautiful fish you can put into your tank. They are native to the islands of Borneo and Sumatra, and they actually differ in color; some are blue, others are orange or red. They live in dark swamps with plenty of decomposing organic material, so they are well adapted to dim, acidic waters with a little of vegetation.

Their size is around 2 cm, so they would fit well in a 5 gallon aquarium, but they would thrive in larger aquariums due to more stable water parameters and easier maintenance. They like densely planted tanks with floating branches and leaves.

When it comes to food, they can be quite picky; they normally don’t like dried foods, but prefer living insects instead.

15. Emerald Dwarf Rasbora (Celestichthys Erythromicron)

The last on the list, but certainly not the least, is the celestichthys erythromicron. It is endemic to the Inle Lake in Myanmar. They are orange with black stripes across its body, so its body looks like that of a tiger.

These tiny fish grow up to 2 cm in size, so they can be kept in an aquarium of 10 gallons (40 liters) because they can be pretty aggressive towards other males. They live in karstic lakes with slightly alkaline water.

You can feed it dried food, but it is best to mix it up with some live foods. These include small insects and shrimp to keep it at optimal conditions.


Small aquariums can be very beautiful. They require a lot of maintenance and work, but in the end it pays off. The key to having a gorgeous nano tank is to not put too many things into it and keep it simple, and of course to maintain it properly.

Hopefully, after reading this article, you have a better idea which fish are best for your nano tank.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
Questions and Answers

I’ve got to get a Bumblebee Gobee: any fish that can swim just above the surface sounds pretty special to me!

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