Best Fish For A 20-Gallon Tank And How Many Can You Fit?

A 20-gallon tank is ideal for a beginner to the hobby and offers lots of exciting options. An aquarium of that size enables you to keep a range of freshwater fish, living plants, and invertebrates, too.

Before you begin your fish keeping journey, you’ll need to know what fish to choose for your aquarium and how many fish can live in a 20-gallon tank.

In this guide, we introduce you to 43 of the best fish for a 20-gallon tank, and much more!

43 Best Fish Species for a 20-Gallon Tank

Here are 43 fish and invertebrate species that you can keep in an aquarium of 20 gallons or larger.

Tetra

1. Cardinal Tetra (Paracheirodon axelrodi)

• Family: Characidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 73^o to 81^o F
• Max. Size: 2 inches
• Lifespan: Up to 2 years

2. Ember Tetra (Hyphessobrycon amandae)

• Family: Characidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 68^o to 82^o F
• Max. Size: 2 inches
• Lifespan: Up to 2 years

3. Rosy Tetra (Hyphessobrycon rosaceus)

• Family: Characidae
• Care Level: Intermediate
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 75^o to 82^o F
• Max. Size: 1.6 inches
• Lifespan: Up to 2 years

4. Flame Tetra (Hyphessobrycon flammeus)

• Family: Characidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 73^o to 82^o F
• Max. Size: 1.6 inches
• Lifespan: Up to 2 years

5. Glowlight Tetra (Hemigrammus erythrozonus)

• Family: Characidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 74^o to 82^o F
• Max. Size: 1.6 inches
• Lifespan: Up to 2 years

Rasbora

6. Lambchop Rasbora (Trigonostigma espei)

• Family: Cyprinidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 73^o to 80^o F
• Max. Size: 1.2 inches
• Lifespan: 3 to 5 years

7. Chili Rasbora (Boraras brigittae)

• Family: Cyprinidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 68^o to 82.4^o F
• Max. Size: 0.8 inches
• Lifespan: 3 to 4 years

8. Least Rasbora (Boraras urophthalmoides)

• Family: Cyprinidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 73.4^o to 82.4^o F
• Max. Size: 1.6 inches
• Lifespan: 4 to 8 years

9. Harlequin Rasbora (Trigonostigma heteromorpha)

• Family: Cyprinidae
• Care Level: Intermediate
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 73^o to 82^o F
• Max. Size: 2 inches
• Lifespan: 5 to 6 years

10. Red Dwarf Rasbora (Microrasbora rubescens)

• Family: Cyprinidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 68^o to 75.2^o F
• Max. Size: 0.8 inches
• Lifespan: 4 to 8 years

11. Dwarf Rasbora (Boraras maculatus)

• Family: Cyprinidae
• Care Level: Intermediate
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 74^o to 79^o F
• Max. Size: 1 inch
• Lifespan: 3 to 5 years

12. Galaxy Rasbora (Microrasboras galaxy)

• Family: Cyprinidae
• Care Level: Intermediate
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 70^o to 75^o F
• Max. Size: 1 inch
• Lifespan: 3 to 5 years

Platies

13. Parrot Platy (Xiphophorus hybrid)

• Family: Poeciliidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 72^o to 75^o F
• Max. Size: 3 inches
• Lifespan: 3 to 5 years

14. Red Platy (Xiphophorus maculatus)

• Family: Poeciliidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 64^o to 77^o F
• Max. Size: 2 inches
• Lifespan: 4 years

15. Coral Platy (Xiphophorus maculatus)

• Family: Poeciliidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 64^o to 77^o F
• Max. Size: 1 inch
• Lifespan: 4 years

Guppies

16. Endler’s Livebearers (Poecilia wingei)

• Family: Poeciliidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 78^o to 80^o F
• Max. Size: 1 inch
• Lifespan: 2 to 3 years

17. Fancy Guppies (Poecilia reticulata)

• Family: Poeciliidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 68^o to 82^o F
• Max. Size: 2.4 inches
• Lifespan: 1 to 3 years

Cichlids

18. Angel Ram Cichlids (Mikrogeophagus ramirezi)

• Family: Cichlidae
• Care Level: Difficult
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 73^o to 80^o F
• Max. Size: 3 inches
• Lifespan: 3 years

19. Electric Blue Ram (Mikrogeophagus ramirezi)

• Family: Cichlidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 78^o to 86^o F
• Max. Size: 3 inches
• Lifespan: 2 to 4 years

20. Umbrella Cichlid (Apistogramma Borelli Opal)

• Family: Cichlidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 72^o to 78^o F
• Max. Size: 2.6 inches
• Lifespan: 2 to 3 years

21. Yellow Dwarf Cichlid (Apistogramma borellii)

• Family: Cichlidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 78^o to 84^o F
• Max. Size: 2.8 inches
• Lifespan: 2 to 3 years

22. Julies (Julidochromis)

• Family: Cichlidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 73^o to 77^o F
• Max. Size: depends on species
• Lifespan: 5 to 8 years

23. Apistogramma (Xiphophorus hellerii)

• Family: Cichlidae
• Care Level: Intermediate
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 72^o to 86^o F
• Max. Size: 3 inches
• Lifespan: 5 to 10 years

Gourami 

24. Honey Gourami (Trichogaster chuna)

• Family: Osphronemidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 72^o to 82^o F
• Max. Size: 3.2 inches
• Lifespan: 4 to 8 years

25. Dwarf Gourami (Trichogaster lalius)

• Family: Osphronemidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 72^o to 82^o F
• Max. Size: 3.5 inches
• Lifespan: 5 to 7 years 

26. Red Dwarf Gourami (Trichogaster lalius)

• Family: Osphronemidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 72^o to 82^o F
• Max. Size: 3.5 inches
• Lifespan: 5 to 7 years

27. Sparkling Gourami (Trichogaster pumila)

• Family: Osphronemidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 70^o to 82^o F
• Max. Size: 1.5 inches
• Lifespan: 5 years

Corydoras Catfish

28. Panda Corydoras Catfish (Corydoras panda)

• Family: Callichthyidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 68^o to 77^o F
• Max. Size: 2 inches
• Lifespan: 10 years

29. Albino Corydoras Catfish (Corydoras paleatus)

• Family: Callichthyidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 68^o to 77^o F
• Max. Size: 2 inches
• Lifespan: 10 years

30. Skunk Corydoras Catfish (Corydoras arcuatus)

• Family: Callichthyidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 68^o to 77^o F
• Max. Size: 2 inches
• Lifespan: 10 years

Shrimp 

31. Red Fire Shrimp (Lysmata debelius)

• Family: Hippolytidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore, algae eater
• Water Conditions: Saltwater, 72^o to 78^o F
• Max. Size: 2 inches
• Lifespan: 1 year

32. Tiger Shrimp (Caridina serrata)

• Family: Penaeidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore, algae eater
• Water Conditions: Freshwater, 68^o to 74^o F
• Max. Size: 1.25 inches
• Lifespan: 1 to 2 years

33. Amano Shrimp (Caridina multidentata)

• Family: Atyidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore, algae eater
• Water Conditions: Freshwater, 64^o to 80^o F
• Max. Size: 2 inches
• Lifespan: 2 to 5 years

Miscellaneous

34. Betta Fish (Betta splendens)

• Family: Osphronemidae
• Care Level: Easy
• Temperament: Semi-aggressive – males cannot be kept together
• Diet: Omnivore
• Water Conditions: Freshwater, 74^o to 79^o F
• Max. Size: 3 inches
• Lifespan: 2 to 3 years

35. Scarlet Badis (Dario dario)

• Family: Osphronemidae
• Care Level: Easy
• Temperament: Semi-aggressive, species-only tank recommended
• Diet: Primarily carnivorous
• Water Conditions: Freshwater, 68^o to 79^o F
• Max. Size: 0.8 inch
• Lifespan: 3 to 6 years 

36. Dwarf Puffer (Carinotetraodon travancoricus)

• Family: Tetraodontidae
• Care Level: Intermediate
• Temperament: Aggressive
• Diet: Primarily carnivorous, prefers live foods
• Water Conditions: Freshwater, 77^o to 82^o F
• Max. Size: 1.4 inches
• Lifespan:  4 years

37. Swordtail (Xiphophorus hellerii)

• Family: Poeciliidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 65^o to 82^o F
• Max. Size: 6 inches
• Lifespan: 5 years

38. Spotted Blue-eye (Pseudomugil gertrudae)

• Family: Pseudomugilidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 73^o to 86^o F
• Max. Size: 1 inch
• Lifespan: 3 to 5 years

39. Dwarf Sucker (Otocinclus macrospilus)

• Family: Loricariidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 73^o to 86^o F
• Max. Size: 1.8 inches
• Lifespan: 3 to 5 years

40. Goldfish (Carassius auratus)

• Family: Cyprinidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 68^o to 74^o F
• Max. Size: 6 inches but depends on species
• Lifespan: 10 to 20 years

41. Bristlenose Catfish (Ancistrus)

• Family: Loricariidae
• Care Level: Easy
• Temperament: Aggressive as adults
• Diet: Omnivore, algae-eaters
• Water Conditions: Freshwater, 73^o to 80^o F
• Max. Size: 3.5 inches
• Lifespan: 12 years

42. Common Molly (Poecilia sphenops)

• Family: Poeciliidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 72^o to 78^o F
• Max. Size: 4.5 inches
• Lifespan: 5 years

43. Mystery Snail (Pomacea bridgesii)

• Family: Poeciliidae
• Care Level: Easy
• Temperament: Peaceful
• Diet: Omnivore
• Water Conditions: Freshwater, 72^o to 78^o F
• Max. Size: 4.5 inches
• Lifespan: 5 years

How Many Fish for a 20-Gallon Tank?

No doubt you will be keen to fill your fish tank with lots of exciting and beautiful fish. So, how many fish can you keep in a 20-gallon tank?

There’s a generally accepted guideline for stocking any aquarium, and that’s to allow one inch of fish per one gallon of water in the tank. However, there are a few other things to consider when stocking your tank, which we’ll discuss later in this guide. 

The most important thing to know is that you shouldn’t overstock your tank. Squeezing too many fish into the tank leads to overcrowding, stress, and poor water conditions, none of which is good for your pets’ health and longevity.

What Is the Biggest Fish You Can Put In A 20-Gallon Tank?

Some hobbyists like to keep one feature fish in a 20-gallon beautifully aquascaped tank. So, what’s the biggest fish you can put in a 20-gallon tank?

Although a 20-gallon tank does offer a fair amount of space, whatever species you choose, the fish must have plenty of room to swim and turn around. For example, extremely active, large fish such as Roseline Sharks need a tank that allows them adequate space to shoal and moves around freely.

Ideally, you want to keep fish that grow no bigger than six inches in a 20-gallon tank, applying the one inch per gallon rule for multiple specimens.

What to Consider When Choosing Fish For a 20-gallon Tank

Adult Size of the Fish

Most of the fish sold in fish stores are juveniles that still have a fair amount of growing to do before they reach adult size. 

For example, some catfish species are sold as cute little creatures no more than a couple of inches long. However, those babies can quickly grow to measure up to a foot long! So, before buying a fish, do plenty of research to find out how big that fish will get.

Behavior and Compatibility

Another vital consideration is the behavior of the fish species you choose.

In nature, many small fish are schooling species that adopt the strategy of safety in numbers. For that reason, those species must be kept in shoals of at least six individuals to avoid the fish becoming stressed and falling prey to fish diseases.

In contrast, some fish are aggressive and do best when kept alone or with a few carefully chosen tank mates for company. Other species are extremely active and need lots of open water swimming space to be happy.

You must do your research before you buy any fish to make sure that the species you choose are compatible. Click this link to find out what fish go together and what species don’t get along.

Water Parameters

Each species of fish has different preferences when it comes to water parameters. Giving your fish the right water conditions is essential if you want your fish to stay healthy and do well.

So, make sure that the fish species you choose all share the same pH, temperature, and water hardness requirements.

Temperature is critical. Both tropical and coldwater fish can suffer from temperature shock if the water temperature is too warm or too cold for them. Make sure that your aquarium has a heater, and monitor the temperature with a good-quality aquarium thermometer. And never try to mix coldwater fish with tropical species.

Stocking Ideas for Your 20-Gallon Fish Tank

The choice of fish for your 20-gallon tank is mind-boggling! So, here are a couple of ideas for a harmonious community tank setup to get you started:

Livebearer Community Tank

• 3 x Guppies
• 2 x Platies
• 2 x Mollies

Tetra Community Tank

• 5 x Neon tetras
• 5 x Glowlight tetras
• 3 x Black Phantom tetras
• 3 x Cherry shrimp

Shrimp are often overlooked as additions to a community tank. That’s a shame, as these industrious little critters make a colorful and exciting addition. Some species eat algae, too, helping to keep your tank clean.

What About Plants?

Live plants are highly beneficial for the ecosystem in your fish tank. As well as adding aesthetic beauty to your aquarium, living plants extract harmful nitrates and CO2 from the water for use as fertilizer. Plants also help to oxygenate the tank as they photosynthesize.

Many hardy aquatic plants are simple to care for and make the ideal choice for beginners. Just double-check that the fish species you’ve chosen are plant-safe.

A few excellent beginner plants that grow well in medium to low light conditions include:

• Anubias
• Amazon Sword
• Vallisneria
• Java moss
• Marimo moss balls
• Hornwort

Conclusion

I hope you enjoyed this guide on the best fish and invertebrates to keep in a 20-gallon tank. A 20-gallon tank is the ideal size aquarium for a beginner, allowing you to enjoy caring for lots of different species without taking up too much space in your home. 

How did you stock your 20-gallon fish tank? We’d love to know!

Tell us about your aquarium in the comments box below, and if you found this article helpful, please share it!