Aquariumcatfish · freshwater
Otocinclus: adult size, tank size & tankmates
The Otocinclus (Otocinclus spp.) grows to about 1.7 in (3.5 cm SL). It needs a tank at least 18 inches long and about 11 gallons. Keep at least 6 together, at 70–79°F.
How big it really gets
Drawn to scale against common tank lengths. Green bars meet the minimum tank length from our sources.
Needs special care. Frequently sold as utilitarian cleanup organisms for newly set up tanks where lack of established biofilm causes high mortality.
Will it fit your tank?
Quick facts
- Adult size
- 1.7 in (3.5 cm SL)
- Minimum tank
- 18 inches long and about 11 gallons
- Temperature
- 70–79°F
- pH
- 5.5–7.5
- Hardness
- 1–12 dGH
- Group size
- 6+
- With other fish
- peaceful
- With its own kind
- peaceful
- Swims
- all levels
- Diet
- specialist
- Care level
- intermediate
- Lifespan
- not stated in sources
Otocinclus tankmates
Checked with the same rules as our tank builder: temperature overlap, pH and hardness, predation and mouth size, fin-nipping and temperament. Tank size is left out here; check it in the builder.
Good tankmates
- Neon TetraAdult ~1.4 in · 70–77°F
- Cardinal TetraAdult ~1.7 in · 73–84°F
- Harlequin RasboraAdult ~2.1 in · 70–82°F
- Ember TetraAdult ~0.9 in · 68–82°F
- Chili RasboraAdult ~0.9 in · 68–82°F
- Celestial Pearl DanioAdult ~1 in · 68–79°F
- Cherry BarbAdult ~2.4 in · 68–81°F
- Rummy-nose TetraAdult ~2.4 in · 73–79°F
- Black Neon TetraAdult ~1.7 in · 73–82°F
- Glowlight TetraAdult ~1.9 in · 75–82°F
Use caution
- Endler's LivebearerNeeds careOtocinclus (1–12 dGH) and Endler's Livebearer (15–35 dGH) prefer different water hardness.
- Dwarf GouramiNeeds careDwarf Gourami can bully smaller, peaceful Otocinclus.
- BettaNeeds careBetta can bully smaller, peaceful Otocinclus.
- AngelfishNeeds careAngelfish can bully smaller, peaceful Otocinclus.
- Nerite SnailOtocinclus (pH 5.5–7.5) and Nerite Snail (pH 8–8.4) prefer different pH.
- Mystery SnailOtocinclus (pH 5.5–7.5) and Mystery Snail (pH unknown) prefer different pH.
- Tiger BarbNeeds careTiger Barb can bully smaller, peaceful Otocinclus.
- MollyNeeds careOtocinclus (1–12 dGH) and Molly (15–30 dGH) prefer different water hardness.
Avoid
- German Blue RamNeeds careOtocinclus (70–79°F) and German Blue Ram (81–86°F) need different temperatures.
- Boesemani RainbowfishOtocinclus (70–79°F) and Boesemani Rainbowfish (81–86°F) need different temperatures.
- Chinese Algae EaterOutgrows tanksChinese Algae Eater grows 8× longer than Otocinclus and may treat it as food.
- Common / Comet GoldfishOutgrows tanksCommon / Comet Goldfish eats small fish, and Otocinclus only grows to about 1.7 in.
- Convict CichlidNeeds careConvict Cichlid is aggressive toward tankmates. Otocinclus is peaceful.
- Electric Blue AcaraNeeds careElectric Blue Acara eats small fish, and Otocinclus only grows to about 1.7 in.
- Iridescent SharkOutgrows tanksIridescent Shark eats small fish, and Otocinclus only grows to about 1.7 in.
- OscarOutgrows tanksOscar eats small fish, and Otocinclus only grows to about 1.7 in.
All 105 species we checked against the Otocinclus
| Species | Verdict | Why |
|---|---|---|
| African Dwarf Frog | Compatible | No conflicts found |
| Amano Shrimp | Compatible | No conflicts found |
| Assassin Snail | Compatible | No conflicts found |
| Bala Shark | Compatible | No conflicts found |
| Bamboo Shrimp | Compatible | No conflicts found |
| Black Neon Tetra | Compatible | No conflicts found |
| Bleeding Heart Tetra | Compatible | No conflicts found |
| Bolivian Ram | Compatible | No conflicts found |
| Bristlenose Pleco | Compatible | No conflicts found |
| Bronze Cory | Compatible | No conflicts found |
| Bumblebee Goby | Compatible | No conflicts found |
| Cardinal Tetra | Compatible | No conflicts found |
| Celestial Pearl Danio | Compatible | No conflicts found |
| Cherry Barb | Compatible | No conflicts found |
| Cherry Shrimp | Compatible | No conflicts found |
| Chili Rasbora | Compatible | No conflicts found |
| Clown Killifish | Compatible | No conflicts found |
| Clown Loach | Compatible | No conflicts found |
| Clown Pleco | Compatible | No conflicts found |
| Cockatoo Dwarf Cichlid | Compatible | No conflicts found |
| Common Pleco | Compatible | No conflicts found |
| Congo Tetra | Compatible | No conflicts found |
| Crystal Red Shrimp | Compatible | No conflicts found |
| Denison Barb | Compatible | No conflicts found |
| Diamond Tetra | Compatible | No conflicts found |
| Dwarf Neon Rainbowfish | Compatible | No conflicts found |
| Ember Tetra | Compatible | No conflicts found |
| Ghost Shrimp | Compatible | No conflicts found |
| Giant Danio | Compatible | No conflicts found |
| Glass Catfish | Compatible | No conflicts found |
| Glowlight Tetra | Compatible | No conflicts found |
| Gold Barb | Compatible | No conflicts found |
| Guppy | Compatible | No conflicts found |
| Harlequin Rasbora | Compatible | No conflicts found |
| Head-and-tail-light Tetra | Compatible | No conflicts found |
| Hillstream Loach | Compatible | No conflicts found |
| Honey Gourami | Compatible | No conflicts found |
| Japanese Trapdoor Snail | Compatible | No conflicts found |
| Julii Cory | Compatible | No conflicts found |
| Kribensis | Compatible | No conflicts found |
| Kuhli Loach | Compatible | No conflicts found |
| Lambchop Rasbora | Compatible | No conflicts found |
| Lemon Tetra | Compatible | No conflicts found |
| Malaysian Trumpet Snail | Compatible | No conflicts found |
| Marbled Hatchetfish | Compatible | No conflicts found |
| Moonlight Gourami | Compatible | No conflicts found |
| Neon Tetra | Compatible | No conflicts found |
| Odessa Barb | Compatible | No conflicts found |
| Panda Cory | Compatible | No conflicts found |
| Pea Puffer | Compatible | No conflicts found |
| Pearl Danio | Compatible | No conflicts found |
| Pearl Gourami | Compatible | No conflicts found |
| Penguin Tetra | Compatible | No conflicts found |
| Peppered Cory | Compatible | No conflicts found |
| Platy | Compatible | No conflicts found |
| Pristella Tetra | Compatible | No conflicts found |
| Pygmy Cory | Compatible | No conflicts found |
| Ramshorn Snail | Compatible | No conflicts found |
| Rosy Barb | Compatible | No conflicts found |
| Rummy-nose Tetra | Compatible | No conflicts found |
| Scissortail Rasbora | Compatible | No conflicts found |
| Serpae Tetra | Compatible | No conflicts found |
| Siamese Algae Eater | Compatible | No conflicts found |
| Silver Hatchetfish | Compatible | No conflicts found |
| Silver Tip Tetra | Compatible | No conflicts found |
| Sparkling Gourami | Compatible | No conflicts found |
| Sterbai Cory | Compatible | No conflicts found |
| Swordtail | Compatible | No conflicts found |
| Upside-down Catfish | Compatible | No conflicts found |
| Weather Loach | Compatible | No conflicts found |
| White Cloud Mountain Minnow | Compatible | No conflicts found |
| Zebra Danio | Compatible | No conflicts found |
| Angelfish | Caution | Angelfish can bully smaller, peaceful Otocinclus. |
| Betta | Caution | Betta can bully smaller, peaceful Otocinclus. |
| Black Skirt Tetra | Caution | Black Skirt Tetra can bully smaller, peaceful Otocinclus. |
| Blood Parrot Cichlid | Caution | Blood Parrot Cichlid can bully smaller, peaceful Otocinclus. |
| Buenos Aires Tetra | Caution | Buenos Aires Tetra can bully smaller, peaceful Otocinclus. |
| Discus | Caution | Otocinclus and Discus only share 79–79°F. That's a tight window. |
| Dwarf Gourami | Caution | Dwarf Gourami can bully smaller, peaceful Otocinclus. |
| Electric Yellow Lab | Caution | Electric Yellow Lab can bully smaller, peaceful Otocinclus.; Otocinclus (pH 5.5–7.5) and Electric Yellow Lab (pH 7.7–8.6) prefer different pH. |
| Endler's Livebearer | Caution | Otocinclus (1–12 dGH) and Endler's Livebearer (15–35 dGH) prefer different water hardness. |
| Fancy Goldfish | Caution | Otocinclus and Fancy Goldfish only share 70–70°F. That's a tight window. |
| Firemouth Cichlid | Caution | Firemouth Cichlid can bully smaller, peaceful Otocinclus. |
| Forktail Blue-eye | Caution | Otocinclus (1–12 dGH) and Forktail Blue-eye (15–30 dGH) prefer different water hardness. |
| Kissing Gourami | Caution | Kissing Gourami grows 7× longer than Otocinclus and may treat it as food.; Kissing Gourami can bully smaller, peaceful Otocinclus. |
| Molly | Caution | Otocinclus (1–12 dGH) and Molly (15–30 dGH) prefer different water hardness. |
| Mystery Snail | Caution | Otocinclus (pH 5.5–7.5) and Mystery Snail (pH unknown) prefer different pH.; Otocinclus (1–12 dGH) and Mystery Snail (unknown dGH) prefer different water hardness. |
| Nerite Snail | Caution | Otocinclus (pH 5.5–7.5) and Nerite Snail (pH 8–8.4) prefer different pH. |
| Paradise Fish | Caution | Paradise Fish can bully smaller, peaceful Otocinclus. |
| Rainbow Shark | Caution | Rainbow Shark grows 4× longer than Otocinclus and may treat it as food.; Rainbow Shark can bully smaller, peaceful Otocinclus. |
| Red-Tail Shark | Caution | Red-Tail Shark can bully smaller, peaceful Otocinclus. |
| Three-spot Gourami | Caution | Three-spot Gourami grows 4× longer than Otocinclus and may treat it as food.; Three-spot Gourami can bully smaller, peaceful Otocinclus. |
| Tiger Barb | Caution | Tiger Barb can bully smaller, peaceful Otocinclus. |
| Variatus Platy | Caution | Otocinclus (1–12 dGH) and Variatus Platy (14–30 dGH) prefer different water hardness. |
| Yoyo Loach | Caution | Yoyo Loach grows 5× longer than Otocinclus and may treat it as food.; Yoyo Loach can bully smaller, peaceful Otocinclus. |
| Boesemani Rainbowfish | Avoid | Otocinclus (70–79°F) and Boesemani Rainbowfish (81–86°F) need different temperatures. |
| Chinese Algae Eater | Avoid | Chinese Algae Eater grows 8× longer than Otocinclus and may treat it as food.; Chinese Algae Eater is aggressive toward tankmates. Otocinclus is peaceful. |
| Common / Comet Goldfish | Avoid | Common / Comet Goldfish eats small fish, and Otocinclus only grows to about 1.7 in. |
| Convict Cichlid | Avoid | Convict Cichlid is aggressive toward tankmates. Otocinclus is peaceful. |
| Electric Blue Acara | Avoid | Electric Blue Acara eats small fish, and Otocinclus only grows to about 1.7 in. |
| German Blue Ram | Avoid | Otocinclus (70–79°F) and German Blue Ram (81–86°F) need different temperatures. |
| Iridescent Shark | Avoid | Iridescent Shark eats small fish, and Otocinclus only grows to about 1.7 in. |
| Oscar | Avoid | Oscar eats small fish, and Otocinclus only grows to about 1.7 in. |
| Pictus Catfish | Avoid | Pictus Catfish eats small fish, and Otocinclus only grows to about 1.7 in. |
| Tinfoil Barb | Avoid | Tinfoil Barb eats small fish, and Otocinclus only grows to about 1.7 in. |
Care notes
Needs: Mature, biologically aged aquarium with abundant natural green algae and aufwuchs; prone to rapid starvation in clean or newly cycled systems.
Group: Obligate social grazer; keep in cohorts of 6 or more to prevent reclusive hiding and feeding inhibition.
Temperament: peaceful toward other fish, peaceful toward its own kind. Lives in the whole tank.
Common questions
How big does a Otocinclus get?
About 1.7 inches (3.5 cm SL) as an adult, according to seriouslyfish.com.
What size tank does a Otocinclus need?
At least 18 inches long and about 11 gallons. The smallest standard tank that meets that is a 20 gallon long.
How many Otocincluss should be kept together?
At least 6. Obligate social grazer; keep in cohorts of 6 or more to prevent reclusive hiding and feeding inhibition.
What fish can live with a Otocinclus?
Species that passed every check include Neon Tetra, Cardinal Tetra, Harlequin Rasbora, Ember Tetra, Chili Rasbora, Celestial Pearl Danio.
Gear for a Otocinclus setup
TankSmallest standard tank that meets its minimum: 20 gallon long (30 in long).Find on Amazon →HeaterAbout 100 W for 20 gallons, holding 70–79°F.Find on Amazon →DriftwoodGrazing wood and biofilm are part of its diet.Find on Amazon →FoodMeaty frozen foods suit its diet.Find on Amazon →Test kitCheck ammonia, nitrite and pH. Cycle the tank before adding fish.Find on Amazon →
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Related guides
Sources
Values come from these pages, in our own words. Status: verified. Last reviewed 2026-10-12.
- seriouslyfish.com /species/otocinclus-macrospilus