Filters are essential for increasing oxygen exchange in your aquarium and boosting its biological filtration capacity. Without an aquarium filter, your fish can live short and painful lives.

An aquarium without a filter also limits your fish choices and requires constant water changes. However, some hardy fish can endure low water filtration and less oxygen.

Fish that don’t need a filter include bettas, goldfish, and zebrafish. According to the Guinness World Book of Records, a goldfish called Tish once lived for 43 years inside a regular fishbowl. In other words, a filter is not necessary for these hardy fish.

Fish waste and decomposing food leftovers contribute to the deterioration of aquarium water quality. In fish tanks with no filters, toxins accumulate, and their breakdown slows.

Suspended particles and dissolved chemicals such as ammonia and nitrates clog fish gills and interfere with their respiratory system, killing vulnerable fish within three to seven days. Signs of stress such as fish floating at the surface may indicate you need a filter.

What fish don’t need a filter?

Here is a summary of fish that don’t need a filter and their primary care requirements:

Fish That Don't Need a Filter
FishBasic care requirements
Betta fishDiet: Plant-based foods, live foods, fish flakes, and pellets
Water temperature: 75°F to 85°F
Water pH: 6.5 and 8
Ammonia and nitrite level: Under 0.5 parts per million
Nitrate level: Under 20 parts per million
Minimum aquarium size: 3 gallons
Frequency of water change: Change at least 20% once every week
Suitable tank plant(s): Fanwort, Limnophila aromatica
Recommended tankmates: Blue Gourami, African Dwarf Frogs, Pictus Catfish
Dwarf pufferfishDiet: Pufferfish are carnivorous.
Water temperature: 74°F to 78°F
Water pH: 7.0 and 7.6
Ammonia and nitrite level: Zero parts per million
Nitrate level: Under 20 parts per million
Minimum aquarium size: 30 gallons
Frequency of water change: Change 20% of the water once every week
Suitable tank plant(s): Anubias, Willow Moss, Java Fern, Cryptocoryne wendtii
Recommended tankmates: Adult Cherry Shrimp, Neon Tetras, Kuhli Loaches
GoldfishDiet: Chopped vegetables, insects, and commercial food pellets twice daily
Water temperature: 68°F to 74°F
Water pH: 7.0 and 8.4
Ammonia and nitrite level: Zero parts per million
Nitrate level: Under 40 parts per million
Minimum aquarium size: 20 gallons
Frequency of water change: Change a third of the tank water once every week
Suitable tank plant(s): Crinum calamistratum, Marimo Moss Ball, Bolbitis Fern
Recommended tankmates: Giant Danios, Dojo Loach, Mystery or Apple Snail
Guppy fishDiet: Omnivorous, though they like brine shrimp
Water temperature: 74°F to 82°FWater pH: 6.8 and 7.6
Ammonia and nitrite level: Under 0.5 parts per million
Nitrate level: Under 25 parts per million
Minimum aquarium size: five gallons
Frequency of water change: Change 30% of the water once every week
Suitable tank plant(s): Christmas Moss, Java Fern, Java Moss, Water Sprite
Recommended tankmates: Swordtails, Platies, Mollies, Cardinal Tetra, Honey Gouramis
Pygmy corydorasDiet: Catfish pellets, frozen foods, flake foods
Water temperature: 72°F to 79°F
Water pH: 6.0 and 8.0
Ammonia and nitrite level: Zero parts per million
Nitrate level: Below five parts per million
Minimum aquarium size: 10 gallons
Frequency of water change: 10% of the water weekly
Suitable tank plant(s): Amazon Swords, Dwarf Hairgrass, Java Fern
Recommended tankmates: Apistogramma, Dwarf Gourami, Ember Tetra, Otocinclus
Sparkling gourami fishDiet: meaty, live, and frozen food like artemia, bloodworms, and daphnia
Water temperature: 75°F to 77°F
Water pH: 6.0 to 8.0
Ammonia and nitrite level: Less than five parts per million
Nitrate level: Less than five parts per million
Minimum aquarium size: 15 gallons
Frequency of water change: 10%-15% of the water weekly
Suitable tank plant(s): Hornwort, Water wisteria
Recommended tankmates: Dwarf Gourami, Neon Tetra, Otocinclus, Small Rasboras
ZebrafishDiet: Algae wafers, chopped vegetables, and high-quality fish flakes twice daily
Water temperature: 70°F to 90°F
Water pH: 6.8 and 8.5
Ammonia and nitrite level: Zero parts per million
Nitrate level: Under 40 parts per million
Minimum aquarium size: 10 gallons
Frequency of water change: Change 25% of the water once every 2-4 weeks
Suitable tank plant(s): Anachris, Amazon Sword, Java Fern, Hornwort
Recommended tankmates: Cory Catfish, Guppies, Swordtail, Angelfish, Kuhli Loach

In the wild, fish do function without artificial filters. They rely on nature to balance their aquatic ecosystem. In your fish tank, use a filter to promote and stabilize the water quality. However, there are fish that can thrive in hardier than optimal conditions. If a filter is off your budget, your choice of fish will reduce. But there is a bunch of fish you can choose from.

Here are some fish that don’t need filters:

1. Betta fish (Betta splendens)

Betta fish don't need a filter

Betta fish are also called Siamese Fighting Fish or Betta splendens. The fish is native to Asia. In the wild, betta fish live in shallow marshes, ponds, and slow-moving streams, growing to an average length of 2.5 inches. You can even manage to keep bettas in tap water for a short period.

Betta fish have a lifespan of three to five years, but some have reportedly lived into their teens at optimal water parameters.

Betta fish breathe through their gills and also through a unique organ known as the labyrinth. When the fish cannot get sufficient oxygen from the surrounding water, the labyrinth allows it to breathe in more air. As a result, the fish can survive longer than most fish in an aquarium with no filter. 

However, avoid overstocking your aquarium because bettas can become aggressive, fight, and injure each other.

See my guidelines on stocking a female betta sorority tank here.

Betta fish requirements

  • Diet: Plant-based foods, live foods, fish flakes, and pellets
  • Water temperature: 75°F to 85°F
  • Water pH: 6.5 and 8
  • Ammonia and nitrite level: Under 0.5 parts per million
  • Nitrate level: Under 20 parts per million
  • Minimum aquarium size: three gallons
  • Frequency of water change: Change at least 20% once every week
  • Suitable tank plant(s): Fanwort, Limnophila aromatica
  • Recommended tankmates: Blue Gourami, African Dwarf Frogs, Pictus Catfish

2. Dwarf puffer fish (Carinotetraodon travancoricus)

Dwarf puffer fish

They are pretty easy to identify. Dwarf pufferfish range in color, but if threatened or stressed, dwarf pufferfish swells with water and “puffs up.” Inflation is their natural defense against aggressive tankmates and predators. Adult dwarf pufferfish grow to only 1.4 inches.

They have a round body that thins towards their tail. Although dwarf pufferfish need no aquarium filter, I don’t recommend this fish to first-time fish keepers because dwarf pufferfish can be pretty challenging to care for.

However, dwarf pufferfish produce a lot of waste and are sensitive to water quality. Without a filter, you’ll need frequent water changes and some plants in your aquarium to reduce water toxicity.

Also, if your room temperature drops below 74°F, you may need a heater to maintain the ideal temperature for a dwarf pufferfish.

Dwarf pufferfish requirements

  • Diet: Pufferfish are carnivorous. Feed them chopped shrimp, squids, and frozen foods
  • Water temperature: 74°F to 78°F
  • Water pH: 7.0 and 7.6
  • Ammonia and nitrite level: Zero parts per million
  • Nitrate level: Under 20 parts per million
  • Minimum aquarium size: 30 gallons
  • Frequency of water change: Change 20% of the water once every week
  • Suitable tank plant(s): Anubias, Java Moss, Java Fern, Cryptocoryne wendtii
  • Recommended tankmates: Adult Cherry Shrimp, Neon Tetras, Kuhli Loaches

3. Goldfish (Carassius auratus)

Goldfish in a filterless aquarium

Goldfish are native to East Asia, where they were associated with luck and fortune. You can keep goldfish in bowls and aquariums without water filters for many years. Goldfish are orange-gold, have large eyes, and are more sensitive to smell and sound.

Although goldfish can reach over 12 inches in the wild, they reach an average length of four inches in an aquarium.

Like betta fish, goldfish have a lung-like structure – the labyrinth – to survive in unfiltered water. Therefore, goldfish can gulp air in low-oxygen environments and breath with significant ease. However, goldfish are slimy and can cloud the water quickly. Therefore, ensure your aquarium is lightly stocked with goldfish to keep them without a filter.

Goldfish requirements

  • Diet: Chopped vegetables, insects, and commercial food pellets twice daily
  • Water temperature: 68°F to 74°F
  • Water pH: 7.0 and 8.4
  • Ammonia and nitrite level: Zero parts per million
  • Nitrate level: Under 40 parts per million
  • Minimum aquarium size: 20 gallons
  • Frequency of water change: Change a third of the tank water once every week
  • Suitable tank plant(s): Crinum calamistratum, Marimo Moss Ball, Bolbitis Fern
  • Recommended tankmates: Giant Danios, Dojo Loach, Mystery or Apple Snail

4. Guppy fish (Poecilia reticulata)

Guppy

You can also keep guppies if you have no plans for an aquarium filter. Guppies are livebearing freshwater fish kept primarily for their color varieties.

Adult guppies measure anywhere between 1.4 inches and 2.4 inches. They are energetic, hardy, and easy to care for. Without a filter, you must make frequent water changes for a clean tank and healthy guppies.

In addition, guppies do not produce large amounts of waste. On top of water changes, adding aquatic plants to the aquarium can help control toxins inside your fish tank.

Whether guppies do not need a filter also depends on the size of your aquarium and the number of guppies you want to keep. Although you can keep guppies without a filter, you need a heater to keep them warm.

Guppy fish requirements

  • Diet: Omnivorous, though they like brine shrimp
  • Water temperature: 74°F to 82°F
  • Water pH: 6.8 and 7.6
  • Ammonia and nitrite level: Under 0.5 parts per million
  • Nitrate level: Under 25 parts per million
  • Minimum aquarium size: five gallons
  • Frequency of water change: Change 30% of the water once every week
  • Suitable tank plant(s): Christmas Moss, Java Fern, Java Moss, Water Sprite
  • Recommended tankmates: Swordtails, Platies, Mollies, Cardinal Tetra, Honey Gouramis

5. Pygmy corydoras (Corydoras pygmaeus)

Corydoras pygmaeus

They are native to South America. They are also often known as pygmy catfish. Pygmy corydoras are tiny freshwater fish that grows between 0.75 inches to one inch in length. They are silvery, with a black line on both sides that start from its snout through the eye and meet at the middle of the tail.

Pygmy corydoras can thrive without a filter in densely planted aquariums. They are shoaling fish. If you decide to keep the catfish in your aquarium, you will need at least ten of them.

Most importantly, pygmy corydoras can also breathe intestinally. If you don’t have a filter, leave a gap between your aquarium’s cover and the water surface for corydoras to come up and take in air.

Pygmy corydoras requirements

  • Diet: Catfish pellets, frozen foods, flake foods
  • Water temperature: 72°F to 79°F
  • Water pH: 6.0 and 8.0
  • Ammonia and nitrite level: Zero parts per million
  • Nitrate level: Under-five parts per million
  • Minimum aquarium size: 10 gallons
  • Frequency of water change: 10% of the water weekly
  • Suitable tank plant(s): Amazon Swords, Dwarf Hairgrass, Java Fern
  • Recommended tankmates: Apistogramma, Dwarf Gourami, Ember Tetra, Otocinclus

6. Sparkling gourami (Trichopsis pumila)

Sparkling gourami fish

The fish are brown with colorful spots on their scales. Male sparkling gouramis have bolder colors than female gouramis. Sparkling gouramis prefer slow-flowing water without turbulence. In addition, sparkling gourami fish can breathe oxygen directly from the air. Therefore, they don’t need a filter.

However, sparkling gouramis love plants. So plant as many aquatic plants in your aquarium as possible. Coupled with periodic water changes, the plants will help with water filtration. Weekly tank maintenance will help move the water, oxygenate the aquarium, and remove toxins. Keep sparkling gouramis in groups of five or six.

Sparkling gourami fish requirements:

  • Diet: meaty, live, and frozen food like artemia, bloodworms, and daphnia
  • Water temperature: 75°F to 77°F
  • Water pH: 6.0 to 8.0
  • Ammonia and nitrite level: Less than five parts per million
  • Nitrate level: Less than five parts per million
  • Minimum aquarium size: 15 gallons
  • Frequency of water change: 10%-15% of the water weekly
  • Suitable tank plant(s): Hornwort, Water wisteria
  • Recommended tankmates: Dwarf Gourami, Neon Tetra, Otocinclus, Small Rasboras

7. Zebrafish (Danio rerio)

Zebrafish

Zebrafish are beautiful fish with blue stripes on their bodies and silvery scales. In the wild, you can find zebrafish in freshwater habitats such as rice paddies, rivers, streams, or ponds. Under optimal temperature, pH, and water quality conditions, adult zebrafish reach between 1.5 inches and two inches. Without filters, zebrafish can live for about three years in an aquarium.

However, given the ideal conditions below, zebrafish lifespan can reach five years. Besides, they also do not require a water heater to thrive. Unlike the livebearing guppies, zebrafish lay eggs. Zebrafish are the easiest egg-laying fish you can breed in your aquarium without a filter. However, I’d recommend a hang-on back (HOB) filter to increase swimming currents for the danios.

Zebrafish requirements

  • Diet: Algae wafers, chopped vegetables, and high-quality fish flakes twice daily
  • Water temperature: 70°F to 90°F
  • Water pH: 6.8 and 8.5
  • Ammonia and nitrite level: Zero parts per million
  • Nitrate level: Under 40 parts per million
  • Minimum aquarium size: 10 gallons
  • Frequency of water change: Change 25% of the water once every two or four weeks
  • Suitable tank plant(s): Anachris, Amazon Sword, Java Fern, Hornwort
  • Recommended tankmates: Cory Catfish, Guppies, Swordtail, Angelfish, Kuhli Loach

References

  • The Guinness World Book of Records. (1999). Oldest Goldfish.
  • The University of Illinois Urbana-Champaign. (2019) Bettas Need More Than Bowls. College of Veterinary Medicine.

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