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Not everyone has space for a large aquarium, but that doesn’t mean you have to miss out on keeping beautiful, fascinating freshwater fish. In fact, many of the most colourful and interesting aquarium species stay surprisingly small throughout their lives, making them perfect for nano tanks, desktop aquariums and compact community setups.
Small fish are often easier to accommodate, require less swimming space than larger species and can create stunning displays when kept in properly sized groups. Whether you’re setting up your very first aquarium or looking to add new livestock to an established nano tank, choosing species that remain small as adults is one of the best decisions you can make.
In this guide, we’ll introduce ten of the best freshwater fish that stay small, along with care tips, recommended tank sizes and compatibility advice.
Why Choose Small Freshwater Fish?
Small fish offer several advantages for beginner and experienced aquarists alike.
Benefits include:
- Suitable for smaller aquariums
- Lower bioload than larger species
- Easier to create attractive community tanks
- Often peaceful and social
- Many display vibrant colours
- Lower equipment and running costs
Remember, even tiny fish deserve appropriately sized aquariums and should never be kept in bowls or undersized tanks.
What Is Considered a Small Aquarium Fish?
For this guide, we’ve focused on species that generally remain under 6 cm (2.5 inches) as adults.
Despite their size, many of these fish are active swimmers and should still be provided with plenty of open swimming space.
Small Freshwater Fish at a Glance
Here are all ten fish side by side. Adult sizes and tank sizes are the minimums we recommend; bigger is always better.
| Fish | Adult size | Minimum tank | Group size | Beginner-friendly? |
|---|---|---|---|---|
| Chili Rasbora | 2 cm | 30 L | 8–10+ | Yes |
| Ember Tetra | 2–2.5 cm | 40 L | 8+ | Yes |
| Celestial Pearl Danio | 2.5 cm | 40 L | 6+ | Yes, with care |
| Neon Tetra | 3–4 cm | 60 L | 6+ | Yes |
| Green Neon Tetra | 2.5–3 cm | 45 L | 8+ | Yes, with care |
| Clown Killifish | 3.5–4 cm | 30 L | Pair or small group | Yes, with care |
| Sparkling Gourami | 3.5–4 cm | 45 L | Pair or small group | Yes, with care |
| Endler’s Livebearer | 3–4 cm | 40 L | Small group | Yes |
| Pygmy Corydoras | 2.5–3 cm | 45 L | 6+ | Yes |
| Otocinclus Catfish | 4–5 cm | 60 L | 6+ | Yes, mature tanks only |
Looking for a tank to match? Browse our small fish tanks, from 30 litre nano kits upwards.
1. Chili Rasbora (
Boraras brigittae
)
The Chili Rasbora is one of the smallest aquarium fish available and one of the most colourful.
Its vibrant red body and black lateral stripe make it a real jewel in planted nano aquariums.
Adult Size
2 cm
Minimum Aquarium Size
30 litres
Temperament
Very peaceful
Keep in Groups?
Yes – at least eight to ten.
Suitable for Beginners?
★★★★★
These tiny fish look particularly impressive in heavily planted aquascapes.
2. Ember Tetra (
Hyphessobrycon amandae
)
Ember Tetras glow with bright orange colouring that stands out beautifully against green plants.
Despite their tiny size, they’re active schooling fish that thrive in peaceful community aquariums.
Adult Size
2–2.5 cm
Minimum Aquarium Size
40 litres
Temperament
Peaceful
Keep in Groups?
Yes – eight or more.
Suitable for Beginners?
★★★★★
3. Celestial Pearl Danio (
Danio margaritatus
)
Also known as the Galaxy Rasbora, this stunning fish features dark blue bodies covered with pearl-like white spots and bright orange fins.
They’re among the most sought-after nano fish.
Adult Size
2.5 cm
Minimum Aquarium Size
40 litres
Temperament
Peaceful
Keep in Groups?
Yes – six or more.
Suitable for Beginners?
★★★★☆
4. Neon Tetra (
Paracheirodon innesi
)
Neon Tetras remain one of the world’s most popular tropical fish for good reason.
Their electric blue stripe and vivid red body make them ideal for community aquariums.
Adult Size
3–4 cm
Minimum Aquarium Size
60 litres
Temperament
Very peaceful
Keep in Groups?
Yes – at least six.
Suitable for Beginners?
★★★★★
5. Green Neon Tetra (
Paracheirodon simulans
)
Smaller than the traditional Neon Tetra, the Green Neon displays a brilliant iridescent blue-green stripe.
They’re particularly attractive in blackwater and planted aquariums.
Adult Size
2.5–3 cm
Minimum Aquarium Size
45 litres
Temperament
Peaceful
Keep in Groups?
Yes – eight or more.
Suitable for Beginners?
★★★★☆
6. Clown Killifish (
Epiplatys annulatus
)
The Clown Killifish is an unusual surface-dwelling species with striking black-and-yellow bands and colourful fins.
They’re ideal for heavily planted nano aquariums with gentle water movement.
Adult Size
3.5–4 cm
Minimum Aquarium Size
30 litres
Temperament
Peaceful
Suitable for Beginners?
★★★★☆
Ensure your aquarium has a tight-fitting lid, as Killifish are excellent jumpers.
7. Sparkling Gourami (
Trichopsis pumila
)
One of the smallest Gourami species, the Sparkling Gourami features iridescent blue-green spots across its body.
These fascinating fish can even produce audible clicking sounds during displays.
Adult Size
3.5–4 cm
Minimum Aquarium Size
45 litres
Temperament
Peaceful
Suitable for Beginners?
★★★★☆
8. Endler’s Livebearer (
Poecilia wingei
)
Closely related to Guppies, Endler’s Livebearers are incredibly colourful despite their tiny size.
Males display vivid combinations of:
- Orange
- Green
- Blue
- Black
Adult Size
3–4 cm
Minimum Aquarium Size
40 litres
Temperament
Peaceful
Suitable for Beginners?
★★★★★
9. Pygmy Corydoras (
Corydoras pygmaeus
)
Unlike larger Corydoras species, Pygmy Corydoras remain tiny throughout their lives.
They spend time both on the substrate and swimming in mid-water.
Adult Size
2.5–3 cm
Minimum Aquarium Size
45 litres
Temperament
Very peaceful
Keep in Groups?
Yes – six or more.
Suitable for Beginners?
★★★★★
A soft sand substrate is recommended to protect their delicate barbels.
10. Otocinclus Catfish (
Otocinclus
species)
Otocinclus are among the best algae-eating fish for nano aquariums.
These peaceful catfish spend their days grazing soft algae from plants, rocks and glass.
Adult Size
4–5 cm
Minimum Aquarium Size
60 litres
Temperament
Peaceful
Keep in Groups?
Yes – six or more.
Suitable for Beginners?
★★★★☆
Otocinclus should only be introduced to mature aquariums with established algae growth.
Honourable Mentions
Several other small freshwater fish narrowly missed our top ten but are also excellent choices:
- Dwarf Pencilfish
- Norman’s Lampeye Killifish
- Least Killifish
- Daisy’s Ricefish
- Black Neon Tetra
- Glowlight Tetra
- Phoenix Rasbora
- Kubotai Rasbora
- Strawberry Rasbora
- Threadfin Rainbowfish
The Best Nano Community Fish Combinations
One of the joys of keeping small fish is creating a balanced nano community.
40-Litre Aquarium
- 10 Chili Rasboras
- 6 Pygmy Corydoras
60-Litre Planted Aquarium
- 12 Ember Tetras
- 6 Otocinclus
- Pair of Sparkling Gouramis
75-Litre Nano Community
- 12 Celestial Pearl Danios
- 8 Pygmy Corydoras
- Pair of Clown Killifish
Always introduce fish gradually and monitor water quality carefully.
Choosing the Right Aquarium
Although these fish remain small, they still need space to thrive.
A good beginner setup should include:
- A quality small fish tank
- Reliable filter
- Adjustable heater
- LED lighting
- Thermometer
- Water conditioner
- Liquid test kit
- Fine gravel or sand substrate
- Live plants
- Natural décor
Stable water conditions are far more important than simply keeping small fish in a small tank.
Feeding Small Freshwater Fish
Most nano fish have tiny mouths and benefit from appropriately sized foods.
Suitable options include:
- Micro pellets
- Crushed tropical flakes
- Baby brine shrimp
- Daphnia
- Cyclops
- Frozen foods
- Live foods
Offering a varied diet helps maintain vibrant colours and strong immune systems.
Common Mistakes When Keeping Small Fish
Even experienced aquarists can make mistakes with nano species.
Avoid:
- Keeping too few schooling fish
- Overstocking a small aquarium
- Mixing with large or aggressive species
- Poor filtration
- Infrequent water changes
- Feeding oversized foods
Small fish are often more confident and display better colours when kept in proper groups.
Frequently Asked Questions
What is the smallest freshwater aquarium fish?
The Chili Rasbora is one of the smallest commonly available aquarium fish, reaching just 2 cm as an adult.
Can small fish live in a nano aquarium?
Yes, provided the aquarium is appropriately filtered, heated and maintained. Even tiny fish need stable water conditions and enough swimming space.
Are small fish easier to care for?
Many are excellent beginner fish, but small aquariums can experience water quality changes more quickly than larger tanks. Regular maintenance remains essential.
Can I mix these species together?
Most of the fish in this guide are peaceful and compatible with one another, provided they share similar water requirements and are kept in suitable group sizes.
Do small fish need a heater?
Most tropical nano fish require a stable temperature between 24°C and 26°C, so an aquarium heater is recommended unless you’re keeping subtropical species.
Final Thoughts
Small freshwater fish prove that you don’t need a huge aquarium to create a beautiful underwater display. Whether you choose the glowing orange Ember Tetra, the jewel-like Celestial Pearl Danio or the vibrant Chili Rasbora, these compact species bring colour, movement and personality to aquariums of all sizes.
The secret to success is providing the right environment. A well-cycled aquarium, excellent water quality, appropriate tank mates and regular maintenance will help even the smallest fish thrive. Combined with live plants and natural décor, these species can transform a modest aquarium into a stunning aquatic landscape.
At Charterhouse Aquatics, we stock a wide range of nano fish, tropical fish, planted aquarium equipment, filters, heaters, aquascaping supplies, fish foods and water care products from leading brands. Whether you’re building your first nano aquarium or expanding an established planted tank, our experienced team is here to help you choose the perfect livestock and equipment.
