Koi Tank Mates

Koi is peaceful, so its tank mates need choosing with care. Here are the 19 freshwater species that pair well with a koi — plus the 230 to avoid — with a live checker you can tune to your own tank.

By The Aquarium DB Team • Updated June 7, 2026 • Full Koi care guide →

Best matches

The best tank mates for a koi

Royal Pleco ✅ Compatible

Medium care · Semi-aggressive · 43 cm · 23–28 °C (73–82 °F)

Peaceful + Semi-aggressive, but with no direct clash here, and their water overlaps around 23–28 °C — no size, zone or temperament conflicts.
Butter Catfish ✅ Compatible

Medium care · Semi-aggressive · 45 cm · 24–28 °C (75–82 °F)

Compatible on the things that matter: shared water near 24–28 °C, workable temperaments, and no predator-and-prey size gap.
Golden Sailfin Pleco ✅ Compatible

Medium care · Semi-aggressive · 45 cm · 22–28 °C (72–82 °F)

Peaceful + Semi-aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
Common Pleco ✅ Compatible

Medium care · Peaceful · 45 cm · 22–28 °C (72–82 °F)

Compatible on the things that matter: shared water near 22–28 °C, workable temperaments, and no predator-and-prey size gap.
Orinoco Sailfin Pleco ✅ Compatible

Medium care · Semi-aggressive · 50 cm · 22–28 °C (72–82 °F)

Peaceful + Semi-aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
Sailfin Pleco ✅ Compatible

Medium care · Peaceful · 50 cm · 22–28 °C (72–82 °F)

Compatible on the things that matter: shared water near 22–28 °C, workable temperaments, and no predator-and-prey size gap.
Walking Catfish ✅ Compatible

Medium care · Aggressive · 50 cm · 20–28 °C (68–82 °F)

Peaceful + Aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
Giant Gourami ✅ Compatible

Medium care · Semi-aggressive · 70 cm · 22–28 °C (72–82 °F)

Compatible on the things that matter: shared water near 22–28 °C, workable temperaments, and no predator-and-prey size gap.
Nile Bichir ✅ Compatible

Medium care · Semi-aggressive · 70 cm · 25–28 °C (77–82 °F)

Peaceful + Semi-aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
Lima Shovelnose Catfish ✅ Compatible

Hard care · Semi-aggressive · 50 cm · 23–30 °C (73–86 °F)

Peaceful + Semi-aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
Gold Zebra Catfish ✅ Compatible

Hard care · Aggressive · 55 cm · 23–27 °C (73–81 °F)

Compatible on the things that matter: shared water near 23–27 °C, workable temperaments, and no predator-and-prey size gap.
Jaguar Cichlid ✅ Compatible

Hard care · Aggressive · 55 cm · 25–30 °C (77–86 °F)

Peaceful + Aggressive, but with no direct clash here, and their water overlaps around 25–28 °C — no size, zone or temperament conflicts.
Spotted Shovelnose Catfish ✅ Compatible

Hard care · Semi-aggressive · 55 cm · 22–28 °C (72–82 °F)

Compatible on the things that matter: shared water near 22–28 °C, workable temperaments, and no predator-and-prey size gap.
Tatauaia Payara ✅ Compatible

Hard care · Aggressive · 59 cm · 24–28 °C (75–82 °F)

Peaceful + Aggressive, but with no direct clash here, and their water overlaps around 24–28 °C — no size, zone or temperament conflicts.
Black Doras Catfish ✅ Compatible

Hard care · Peaceful · 60 cm · 22–28 °C (72–82 °F)

Compatible on the things that matter: shared water near 22–28 °C, workable temperaments, and no predator-and-prey size gap.
Lyre Tail Pleco ✅ Compatible

Hard care · Semi-aggressive · 63 cm · 21–27 °C (70–81 °F)

Peaceful + Semi-aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
Mbu Puffer ✅ Compatible

Hard care · Aggressive · 67 cm · 24–28 °C (75–82 °F)

Peaceful + Aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
Ocellaris Peacock Bass ✅ Compatible

Hard care · Aggressive · 70 cm · 24–30 °C (75–86 °F)

Compatible on the things that matter: shared water near 24–28 °C, workable temperaments, and no predator-and-prey size gap.
Wolf Cichlid ✅ Compatible

Hard care · Aggressive · 72 cm · 24–30 °C (75–86 °F)

Peaceful + Aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.

With caution

Koi tank mates that can work with care

Adolf's Cory ⚠️ With caution

Medium care · Peaceful · 5.5 cm · 22–26 °C (72–79 °F)

Water hardness preferences differ (Koi 9–18 vs Adolf's Cory 1–8 dGH).
Agassiz's Corydoras ⚠️ With caution

Easy care · Peaceful · 6 cm · 22–28 °C (72–82 °F)

Koi may bully the smaller Agassiz's Corydoras, though its armour makes it a hard meal — give it caves and driftwood to retreat into.
Amano Shrimp ⚠️ With caution

Easy care · Peaceful · 5 cm · 18–28 °C (64–82 °F)

Koi may eat Amano Shrimp or pick off its shrimplets — a densely planted tank with moss gives them a fighting chance.
Angelicus Synodontis ⚠️ With caution

Medium care · Semi-aggressive · 25 cm · 23–27 °C (73–81 °F)

Koi may bully the smaller Angelicus Synodontis, though its armour makes it a hard meal — give it caves and driftwood to retreat into.
Assassin Snail ⚠️ With caution

Easy care · Peaceful · 3 cm · 22–26 °C (72–79 °F)

Koi may bully the smaller Assassin Snail, though its armour makes it a hard meal — give it caves and driftwood to retreat into.
Axelrod's Cory ⚠️ With caution

Easy care · Peaceful · 5 cm · 23–28 °C (73–82 °F)

Koi may bully the smaller Axelrod's Cory, though its armour makes it a hard meal — give it caves and driftwood to retreat into.
Bamboo Shrimp ⚠️ With caution

Medium care · Peaceful · 8 cm · 22–27 °C (72–81 °F)

Koi may eat Bamboo Shrimp or pick off its shrimplets — a densely planted tank with moss gives them a fighting chance.
Bandit Corydoras ⚠️ With caution

Easy care · Peaceful · 5 cm · 22–27 °C (72–81 °F)

Koi may bully the smaller Bandit Corydoras, though its armour makes it a hard meal — give it caves and driftwood to retreat into.

+ 83 more “with caution” pairings — see the interactive checker above.

Avoid

Fish to avoid keeping with a koi

Wels Catfish ⛔ Avoid

Hard care · Aggressive · 300 cm · 15–25 °C (59–77 °F)

Koi is bite-sized to a 300 cm predatory wels catfish — it will be eaten.
Alligator Gar ⛔ Avoid

Hard care · Aggressive · 250 cm · 24–28 °C (75–82 °F)

Koi is bite-sized to a 250 cm predatory alligator gar — it will be eaten.
Clown Loach ⛔ Avoid

Medium care · Peaceful · 30 cm · 25–30 °C (77–86 °F)

Clown Loach is bite-sized to a 90 cm koi — it will be eaten.
Cuban Cichlid ⛔ Avoid

Hard care · Aggressive · 30 cm · 24–28 °C (75–82 °F)

Koi (90 cm) is big enough to swallow the 30 cm Cuban Cichlid whole.
Flowerhorn Cichlid ⛔ Avoid

Medium care · Aggressive · 30 cm · 25–30 °C (77–86 °F)

Koi (90 cm) is big enough to swallow the 30 cm Flowerhorn Cichlid whole.
Goldfish ⛔ Avoid

Medium care · Peaceful · 30 cm · 18–22 °C (64–72 °F)

Size gap is too large (90 vs 30 cm): Koi will treat Goldfish as food.
Kissing Gourami ⛔ Avoid

Medium care · Semi-aggressive · 30 cm · 22–28 °C (72–82 °F)

Kissing Gourami is bite-sized to a 90 cm koi — it will be eaten.
Peacock Eel ⛔ Avoid

Medium care · Semi-aggressive · 30 cm · 22–28 °C (72–82 °F)

Koi (90 cm) is big enough to swallow the 30 cm Peacock Eel whole.

+ 222 more to avoid — the checker above flags every one.

Interactive tool

Check any fish against a koi

Dial in your exact tank size and filter by result — the checker scores every species in our database against a koi, with the reasoning for each verdict.

Tank-mate checker

Will it live with a Koi?

We compare each fish against your koi on temperament, size, water parameters and swimming zone. Set your tank size and filter the results.

Your tank: 3800 L (~1004 gal)

Black Doras Catfish✅ Compatible
Peaceful · 60 cm · Hard care · 22–28 °C (72–82 °F)
- Compatible on the things that matter: shared water near 22–28 °C, workable temperaments, and no predator-and-prey size gap.
Butter Catfish✅ Compatible
Semi-aggressive · 45 cm · Medium care · 24–28 °C (75–82 °F)
- Compatible on the things that matter: shared water near 24–28 °C, workable temperaments, and no predator-and-prey size gap.
Common Pleco✅ Compatible
Peaceful · 45 cm · Medium care · 22–28 °C (72–82 °F)
- Compatible on the things that matter: shared water near 22–28 °C, workable temperaments, and no predator-and-prey size gap.
Giant Gourami✅ Compatible
Semi-aggressive · 70 cm · Medium care · 22–28 °C (72–82 °F)
- Compatible on the things that matter: shared water near 22–28 °C, workable temperaments, and no predator-and-prey size gap.
Gold Zebra Catfish✅ Compatible
Aggressive · 55 cm · Hard care · 23–27 °C (73–81 °F)
- Compatible on the things that matter: shared water near 23–27 °C, workable temperaments, and no predator-and-prey size gap.
Golden Sailfin Pleco✅ Compatible
Semi-aggressive · 45 cm · Medium care · 22–28 °C (72–82 °F)
- Peaceful + Semi-aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
Jaguar Cichlid✅ Compatible
Aggressive · 55 cm · Hard care · 25–30 °C (77–86 °F)
- Peaceful + Aggressive, but with no direct clash here, and their water overlaps around 25–28 °C — no size, zone or temperament conflicts.
Lima Shovelnose Catfish✅ Compatible
Semi-aggressive · 50 cm · Hard care · 23–30 °C (73–86 °F)
- Peaceful + Semi-aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
Lyre Tail Pleco✅ Compatible
Semi-aggressive · 63 cm · Hard care · 21–27 °C (70–81 °F)
- Peaceful + Semi-aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
Mbu Puffer✅ Compatible
Aggressive · 67 cm · Hard care · 24–28 °C (75–82 °F)
- Peaceful + Aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
Nile Bichir✅ Compatible
Semi-aggressive · 70 cm · Medium care · 25–28 °C (77–82 °F)
- Peaceful + Semi-aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
Ocellaris Peacock Bass✅ Compatible
Aggressive · 70 cm · Hard care · 24–30 °C (75–86 °F)
- Compatible on the things that matter: shared water near 24–28 °C, workable temperaments, and no predator-and-prey size gap.
Orinoco Sailfin Pleco✅ Compatible
Semi-aggressive · 50 cm · Medium care · 22–28 °C (72–82 °F)
- Peaceful + Semi-aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
Royal Pleco✅ Compatible
Semi-aggressive · 43 cm · Medium care · 23–28 °C (73–82 °F)
- Peaceful + Semi-aggressive, but with no direct clash here, and their water overlaps around 23–28 °C — no size, zone or temperament conflicts.
Sailfin Pleco✅ Compatible
Peaceful · 50 cm · Medium care · 22–28 °C (72–82 °F)
- Compatible on the things that matter: shared water near 22–28 °C, workable temperaments, and no predator-and-prey size gap.
Spotted Shovelnose Catfish✅ Compatible
Semi-aggressive · 55 cm · Hard care · 22–28 °C (72–82 °F)
- Compatible on the things that matter: shared water near 22–28 °C, workable temperaments, and no predator-and-prey size gap.
Tatauaia Payara✅ Compatible
Aggressive · 59 cm · Hard care · 24–28 °C (75–82 °F)
- Peaceful + Aggressive, but with no direct clash here, and their water overlaps around 24–28 °C — no size, zone or temperament conflicts.
Walking Catfish✅ Compatible
Aggressive · 50 cm · Medium care · 20–28 °C (68–82 °F)
- Peaceful + Aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
Wolf Cichlid✅ Compatible
Aggressive · 72 cm · Hard care · 24–30 °C (75–86 °F)
- Peaceful + Aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
Bichir⚠️ With caution
Semi-aggressive · 45 cm · Medium care · 24–28 °C (75–82 °F)
- Koi may hunt Bichir, fry or shrimplets — safest in a heavily planted tank.
Black Belt Cichlid⚠️ With caution
Aggressive · 35 cm · Hard care · 24–30 °C (75–86 °F)
- Watch for Koi picking off any black belt cichlid small enough to fit in its mouth.
Black Ghost Knifefish⚠️ With caution
Semi-aggressive · 45 cm · Hard care · 24–28 °C (75–82 °F)
- Koi may hunt Black Ghost Knifefish, fry or shrimplets — safest in a heavily planted tank.
Clown Knifefish⚠️ With caution
Aggressive · 90 cm · Hard care · 24–28 °C (75–82 °F)
- Expect Clown Knifefish to harass Koi at times; give dense cover and watch them at feeding.
Elephant-nose Knifefish⚠️ With caution
Peaceful · 35 cm · Hard care · 24–29 °C (75–84 °F)
- Water hardness preferences differ (Koi 9–18 vs Elephant-nose Knifefish 1–8 dGH).
- Elephant-nose Knifefish is small enough to tempt Koi; only risk it in a densely planted setup with hiding spots.
Fahaka Puffer⚠️ With caution
Aggressive · 45 cm · Hard care · 24–26 °C (75–79 °F)
- Watch for Koi picking off any fahaka puffer small enough to fit in its mouth.
Fire Eel⚠️ With caution
Semi-aggressive · 100 cm · Medium care · 24–28 °C (75–82 °F)
- Expect Fire Eel to harass Koi at times; give dense cover and watch them at feeding.
Imperial Flower Loach⚠️ With caution
Semi-aggressive · 50 cm · Hard care · 15–22 °C (59–72 °F)
- Koi may hunt Imperial Flower Loach, fry or shrimplets — safest in a heavily planted tank.
Malawi Trout Cichlid⚠️ With caution
Aggressive · 35 cm · Hard care · 24–28 °C (75–82 °F)
- Koi may hunt Malawi Trout Cichlid, fry or shrimplets — safest in a heavily planted tank.
Midas Cichlid⚠️ With caution
Aggressive · 35 cm · Hard care · 24–28 °C (75–82 °F)
- Midas Cichlid is small enough to tempt Koi; only risk it in a densely planted setup with hiding spots.
Oscar⚠️ With caution
Aggressive · 35 cm · Medium care · 23–28 °C (73–82 °F)
- Koi may hunt Oscar, fry or shrimplets — safest in a heavily planted tank.
Red Devil Cichlid⚠️ With caution
Aggressive · 38 cm · Medium care · 24–28 °C (75–82 °F)
- Watch for Koi picking off any red devil cichlid small enough to fit in its mouth.
Redtail Catfish⚠️ With caution
Aggressive · 120 cm · Hard care · 24–27 °C (75–81 °F)
- Redtail Catfish and Koi are close in size, but the aggressive one tends to dominate — add koi in a group to spread the pressure.
- Your 3800 L tank is below the ~5700 L this pairing really wants — crowding raises aggression.
Spotted Gar⚠️ With caution
Aggressive · 90 cm · Hard care · 18–26 °C (64–79 °F)
- Expect Spotted Gar to harass Koi at times; give dense cover and watch them at feeding.
Spotted Knifefish⚠️ With caution
Aggressive · 45 cm · Hard care · 22–28 °C (72–82 °F)
- Spotted Knifefish is small enough to tempt Koi; only risk it in a densely planted setup with hiding spots.
True Red Terror Cichlid⚠️ With caution
Aggressive · 35 cm · Hard care · 22–28 °C (72–82 °F)
- True Red Terror Cichlid is small enough to tempt Koi; only risk it in a densely planted setup with hiding spots.
Alligator Gar⛔ Not recommended
Aggressive · 250 cm · Hard care · 24–28 °C (75–82 °F)
- Koi is bite-sized to a 250 cm predatory alligator gar — it will be eaten.
- Alligator Gar is aggressive and may chase or nip the smaller Koi — plant heavily and break up sight lines.
Clown Loach⛔ Not recommended
Peaceful · 30 cm · Medium care · 25–30 °C (77–86 °F)
- Clown Loach is bite-sized to a 90 cm koi — it will be eaten.
Cuban Cichlid⛔ Not recommended
Aggressive · 30 cm · Hard care · 24–28 °C (75–82 °F)
- Koi (90 cm) is big enough to swallow the 30 cm Cuban Cichlid whole.
Flowerhorn Cichlid⛔ Not recommended
Aggressive · 30 cm · Medium care · 25–30 °C (77–86 °F)
- Koi (90 cm) is big enough to swallow the 30 cm Flowerhorn Cichlid whole.
Goldfish⛔ Not recommended
Peaceful · 30 cm · Medium care · 18–22 °C (64–72 °F)
- Size gap is too large (90 vs 30 cm): Koi will treat Goldfish as food.
Kissing Gourami⛔ Not recommended
Semi-aggressive · 30 cm · Medium care · 22–28 °C (72–82 °F)
- Kissing Gourami is bite-sized to a 90 cm koi — it will be eaten.
Peacock Eel⛔ Not recommended
Semi-aggressive · 30 cm · Medium care · 22–28 °C (72–82 °F)
- Koi (90 cm) is big enough to swallow the 30 cm Peacock Eel whole.
Wels Catfish⛔ Not recommended
Aggressive · 300 cm · Hard care · 15–25 °C (59–77 °F)
- Koi is bite-sized to a 300 cm predatory wels catfish — it will be eaten.
- Wels Catfish is aggressive and may chase or nip the smaller Koi — plant heavily and break up sight lines.
- Your 3800 L tank is below the ~20000 L this pairing really wants — crowding raises aggression.

Compatibility is computed from each species' care data — a strong starting point, not a guarantee. Individual temperament varies, so always introduce new fish slowly and watch them.

Setting up a koi community tank

Give the group a stable, planted 3800 L+ tank with a gentle filter, a reliable heater and plenty of cover — broken sight lines and hiding spots let mid-water and bottom dwellers keep out of each other's way. Cycle it fully and stock gradually.

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How to choose

How to choose the right tank mates for a koi

As a peaceful species, koi is easily bullied — favour other calm, non-nippy fish and steer clear of boisterous or aggressive tank mates. It ranges across the whole water column, so tank mates that keep to one level help reduce friction.

Koi grows to about 90 cm, so avoid tank mates small enough to be seen as food — as a rule of thumb, skip anything under roughly 45 cm. Match its water, too: aim for 4–28 °C (39–82 °F), pH 6.5–8.5 and 9–18 dGH. Fish needing very different conditions — coldwater species, or hard-water lovers against a soft-water fish — rarely thrive side by side.

Koi is a shoaling fish — stock a group of 3+ of its own kind first, then build compatible tank mates around them. Whatever you add, introduce new fish slowly, watch for bullying in the first days, and have a backup plan if temperaments clash.

FAQ

Frequently asked questions

Can a koi live with other fish?

Yes — with the right companions. Our checker finds 19 compatible freshwater species for koi. Pick calm, similarly-sized fish that share its water needs and add them to a mature, well-planted tank.

What is the best tank mate for a koi?

Easy, peaceful, similarly-sized species top the list — for example Royal Pleco, Butter Catfish, Golden Sailfin Pleco. Use the checker above to match against your own tank size.

What fish should you avoid keeping with a koi?

Avoid Wels Catfish, Alligator Gar, Clown Loach and similar — usually a temperature, size or temperament clash. The full "avoid" list below gives the reason for each.

How big a tank do koi tank mates need?

Start from Koi's own minimum and scale up with every addition. The checker above defaults to a 3800 L community tank and flags pairings that need more room — drag the slider to match your setup.

← Back to the full Koi care guide