The Best Fish for Small Freshwater Aquariums (And 2 Incredible Invertebrates)

by Kevin

Small planted aquarium ready for fish.

Small aquariums, which I am defining as tanks ranging from 5 to 15 gallons, are perfect for smaller spaces and apartments, but selecting the right kind of fish is crucial because space and water volume is limited.

This article outlines what you need to think about when keeping a small aquarium and how to choose the right fish for your tank.

Considerations for Small Aquariums:

  1. Water Quality: Small tanks require diligent maintenance, as water parameters can fluctuate rapidly.
  2. Lighting: Proper lighting not only showcases the fish but is crucial for live plants, which in turn help maintain water quality.
  3. Substrate: Choose a substrate that suits the needs of the fish and plants. Some fish prefer sandy substrates, while others are fine with gravel.
  4. Water Movement: Gentle water movement is preferred for most small fish species. Strong currents can stress them.
  5. Plants vs. Decorations: Live plants are beneficial for water quality and provide natural hiding spots, but artificial decorations can also be used effectively.
  6. Aquascaping: Provide appropriate plants and decorations for hiding and exploring.
  7. Stocking Levels: Avoid overstocking to ensure the health and well-being of the fish.
  8. Regular Maintenance: Frequent water changes and testing are vital to maintaining water quality.
  9. Temperature Control: Ensure the water temperature is consistent and suitable for the specific fish species.
  10. Feeding: Overfeeding can quickly lead to water quality issues in small tanks. Feed small amounts and remove uneaten food.
  11. Observation: Regularly observe fish behavior and health. Early detection of problems can prevent major issues in a small ecosystem.
  12. Compatibility: Research the compatibility of fish species to avoid aggression or stress. Some species are territorial or have specific social needs.

Best Tropical Fish Species for Small Aquariums

My top picks:

1. Betta Fish (Betta splendens)

Halfmoon, blue and white betta fish in a planted aquarium.
Male halfmoon betta fish in a planted aquarium

Size and Temperament: Growing up to 3 inches, bettas are known for their vibrant colors and flowing fins. They are solitary fish and best kept alone due to their aggressive nature towards other bettas and many species of tropical fish (check out my betta tank mate compatibility guide to learn more).

Aquarium Conditions: Bettas thrive best in a 5-gallon tank with a gentle filter and heater, as they prefer warm, stable water temperatures (76-78 Fahrenheit or 24.4-25.6 Celsius is ideal).

2. Neon Tetras (Paracheirodon innesi)

Schooling Fish: These small, brightly colored fish are best kept in groups of at least six. They grow up to 1.5 inches, making them perfect for small tanks.

Aquarium Setup: Neon tetras prefer a planted aquarium with subdued lighting and peaceful tank mates (like guppies). A 10-gallon tank is great for a small school but consider a 20-gallon long if you want a larger school or want to keep other species of tropical fish with your neons. Providing softer water (a pH lower than 7) helps these fish feel comfortable. If you want to learn more about neon tetras, check out my quick guide on these fascinating fish.

3. Guppies (Poecilia reticulata)

Two male guppies in a planted tank

Variety and Size: Known for their vibrant colors and easy care, guppies are small fish, typically about 2 inches long.

Tank Requirements: They can live in a 5-gallon tank, but a larger space is recommended if you plan to breed them, as they reproduce rapidly. Check out my article on male vs female guppies if you want to learn more about these fish.

4. Dwarf Gourami (Trichogaster lalius)

Dwarf gourami in a small planted aquarium.
Dwarf gourami, a species native to South Asia

Temperament and Size: These peaceful fish are suitable for community tanks and grow up to 3.5 inches.

Aquarium Needs: A 10-gallon or 15-gallon tank is ideal for a pair of dwarf gouramis, with plenty of hiding spots and plants. Check out my quick guide on dwarf gouramis for an overview of how to care for these fish.

5. Cherry Shrimp (Neocaridina davidi)

Red cherry shrimp in a planted aquarium.

Non-Fish Option: While not fish, cherry shrimp are excellent for small tanks and help keep the environment clean by feeding on algae.

Tank Conditions: They thrive in planted tanks with plenty of hiding spaces and coexist best with small, peaceful fish. If you want to learn more about keeping shrimp, take a look at my article on freshwater aquarium shrimp.

6. Pygmy Corydoras (Corydoras pygmaeus)

Pygmy corydoras resting on java moss.

Small Catfish: These tiny catfish grow up to 1 inch and are peaceful bottom-dwellers, ideal for community tanks.

Tank Setup: A 10-gallon tank with soft substrate is recommended for these schooling fish, and consider a 15-gallon aquarium if you want to keep a school of these corys with other, peaceful tank mates.

7. Zebra Danio (Danio rerio)

School of Zebra danios.

Active Swimmers: Zebra danios are hardy and active, growing up to 2 inches. They are best kept in groups.

Aquarium Size: A minimum of a 10-gallon tank is recommended, but a larger tank is great if you plan to keep other fish with your Zebra danios.

8. White Cloud Mountain Minnow (Tanichthys albonubes)

White cloud minnow in a planted aquarium.

Cold Water Fish: Unique for their ability to thrive in cooler temperatures, they are a great option for unheated tanks.

Tank Requirements: A 10-gallon tank suits a small group of these hardy, peaceful fish.

9. Harlequin Rasbora (Trigonostigma heteromorpha)

Harlequin rasbora in small aquarium.

Appearance and Size: Known for their distinctive black patch and orange body, they grow to about 2 inches.

Tank Conditions: A group of at least 6 rasboras requires a minimum of a 10-gallon tank. They prefer a well-planted aquarium with soft, slightly acidic water.

10. Endler’s Livebearer (Poecilia wingei)

Male Endler's livebearer in a planted tank.
Male Endler’s Livebearer

Colorful and Active: These vibrant and active fish are similar to guppies but smaller, reaching about 1.8 inches.

Aquarium Setup: A 5-gallon tank can house a small group, but more space is better, especially for breeding.

11. Bristlenose Pleco (Ancistrus sp.)

Bristlenose or Bushymouth catfish in a planted aquarium.

Algae Eaters: Also known as Bushymouth catfish, these bottom dwellers are larger than other small-tank suitable species (growing up to 4-5 inches), but they are excellent for algae control.

Tank Requirements: A 10-gallon aquarium is suitable for baby and juvenile bristlenose plecos (when they are 1-3 inches in size), but a 20-gallon tank is the minimum for an adult, and should have plenty of hiding spots and wood for grazing and rasping.

12. Killifish (more than 320 species)

Red-Spotted Killi (Aphyosemion cognatum) in a planted tank.
Red-Spotted Killi (Aphyosemion cognatum)

Diverse Group: There are many small species of killifish suitable for small aquariums.

Specific Needs: Their requirements vary, but many can be kept in 5 to 10-gallon tanks. Research the specific needs of the killifish species that interests you.

13. Celestial Pearl Danio (Danio margaritatus)

Celestial Pearl Danio (Celestichthys margaritatus).

Size and Behavior: Tiny yet colorful, they grow up to 1 inch and are peaceful, making them suitable for community tanks.

Aquarium Setup: A 10-gallon tank is suitable for a small group, with plenty of plants and hiding spaces.

14. Ember Tetra (Hyphessobrycon amandae)

Ember tetra for small aquarium.

Small and Peaceful: These tiny, bright orange-red fish grow up to 1 inch and are very peaceful.

Tank Conditions: A 10-gallon planted tank with softer (acidic) water is ideal.

15. Honey Gourami (Trichogaster chuna)

Honey gourami for small aquarium.

Temperament and Size: Similar to dwarf gouramis but slightly smaller and very peaceful.

Aquarium Needs: A 10-gallon tank with plants and gentle filtration is suitable.

16. Sparkling Gourami (Trichopsis pumila)

Sparkling gourami for small tank.

Size and Behavior: Also known as the Pygmy Gourami, these tiny gouramis grow only up to 1.5 inches and are known for their quiet croaking sounds.

Tank Requirements: Ideal for 10-15 gallon tanks, they prefer densely planted setups and can be kept in pairs or small groups.

17. African Dwarf Frog

African dwarf frog for small aquarium.

Non-Fish Option: While not a fish, these small amphibians are a unique addition to a small aquarium.

Aquarium Setup: A 10-gallon tank with easy access to the surface for breathing and places to hide is suitable.

18. Black Tiger Badis (Dario sp. ‘Myanmar’)

Black Tiger Badis for small aquairum.

Small and Colorful: Also known as a Black Tiger Dario, these fish reach a maximum size of 1-1.5 inches and are known for the impressive tiger striping and black and orange coloration on the male.

Tank Conditions: A 5-gallon planted tank with hiding spots is ideal, but they can be territorial, so avoid keeping multiple males in one tank and monitor your fish closely.

19. Pea Pufferfish (Carinotetraodon travancoricus)

Pea Puffer or Dwarf Puffer (Carinotetraodon travancoricus) in planted aquarium.

Unique and Personable: These tiny puffers grow to about 1 inch and have fascinating behaviors.

Specific Needs: A 15-gallon tank for a pair of puffers, but don’t keep multiple males together. Provide plenty of hiding spots. They require a diet of snails and other live foods.

20. Mosquito Rasbora (Boraras brigittae)

Chili rasbora in a planted aquarium.

Tiny Schooling Fish: Also known as Chili Rasboras (for their red color), these fish grow to about 0.8 inches, making them ideal for nano tanks.

Aquarium Setup: A 5-gallon tank is adequate for a small school, but a 10-gallon is ideal if you plan to keep other fish with them. A densely planted aquarium is perfect for these fish.

21. Clown Killifish (Epiplatys annulatus)

Clown Killifish for small aquarium.

Distinctive Appearance: These tiny fish, growing up to 1.5 inches, are known for their striking color patterns.

Tank Requirements: A 10-gallon tank can accommodate a small group, but they prefer a heavily planted environment and a peaceful community.

22. Marble Hatchetfish (Carnegiella strigata)

Marble Hatchetfish for small aquarium.

Surface Dweller: These fish hang out at the water’s surface. They have a unique look, having a rounded hatchet shaped body that extends from their neck to tail.

Aquarium Setup: A 10-gallon tank with a tightly fitting lid (they can jump) and plenty of floating plants is the minimum, but they prefer being in groups of 6 or more, so consider getting a 20-gallon long.

23. Otocinclus Catfish

Otocinclus algae eater in a planted tank.

Small Algae Eater: Growing to about 2 inches, these catfish are excellent algae cleaners for small tanks. They also make excellent tank mates for betta fish because they don’t compete for the same food and are not colorful.

Specific Needs: A 10-gallon planted tank with a gentle current and plenty of algae or supplemental feeding is ideal. Take a look at my quick guide on otocinclus for an overview of caring for this fish.

24. Thai Micro Crabs

Thai micro crab in a small aquarium.

Tiny Invertebrate: Reaching about half an inch in size (1.3 cm), these tiny freshwater crabs are fully aquatic and are ideal for aquariums under 3 gallons.

Tank Setup: A 2-gallon to 3-gallon tank is suitable for a group of 5 crabs. They are incredible shy creatures and will hide most of the day so don’t expect to see your crabs, especially if you keep them in a larger tank. Check out my tutorial on how to set up a tank for Thai micro crabs if you want to learn more about keeping these fascinating crabs.

Advanced Care Tips for Small Aquariums

Aquascaping Techniques: Use rocks, driftwood, and plants to create a natural and aesthetically pleasing environment. This also helps in creating territories and reducing stress among fish.

Water Parameters: Regular testing for ammonia, nitrite, nitrate, and pH levels is essential. Small tanks are more prone to rapid changes in water quality.

Species-Specific Diets: Understand the dietary needs of each species. Some may require specialized foods, such as live or frozen varieties.

Breeding Considerations: If you are interested in breeding, research the breeding habits and requirements of the chosen species. Some may breed readily in community tanks, while others need specific conditions.

Conclusion

Small aquariums offer a unique opportunity to create a miniature underwater world. By choosing the right fish and providing appropriate care, these tanks can be just as rewarding as larger setups.

The key is to understand the needs of each species and to create a balanced, healthy environment that mimics their natural habitat as closely as possible. Remember, the well-being of the aquatic life should always be the top priority, so make sure you research each species thoroughly.

If you enjoyed this article, check out my article on setting up a simple aquascape for guppies and shrimp, or learn about the basics of aquascaping.

As always, stay zen.