Fish guide
Otocinclus Catfish
Otocinclus vittatus (representative common species; several Otocinclus species are sold under the same trade name)
Otocinclus Catfish
Quick Reference
- Difficulty
- Moderate. Peaceful and small, but sensitive after import and vulnerable to starvation in new or overly clean aquariums.
- Adult Size
- Usually 1.25-2 inches (3-5 cm), depending on species; O. vittatus reaches about 1.3 inches (3.3 cm).
- Minimum Tank
- 15 gallons for a group of 6; 20 gallons or larger is preferred because it provides more grazing surface and stable water quality.
- Temperature
- 70-78°F (21-26°C); approximately 72-76°F (22-24°C) suits most commonly traded species.
- pH
- 6.0-7.5; slightly acidic to neutral is preferred.
- GH
- 2-15 dGH; soft to moderately hard water
- KH
- 2-8 dKH; maintain enough buffering for stable pH.
- Temperament
- Very peaceful and shy
- Diet
- Specialized grazer / omnivorous aufwuchs feeder; consumes algae, biofilm, microorganisms, and soft plant material.
- Swimming Level
- Bottom and lower-to-middle surfaces; frequently rests and grazes on glass, leaves, wood, and hardscape.
- Social Type
- Gregarious, social catfish
- Minimum Group
- At least 6 of similar size and species type; larger groups are appropriate when the aquarium can provide enough food.
- Community Safe
- Yes, with small peaceful tank mates
- Plant Safe
- Yes. Healthy plants are normally unharmed; otocinclus graze algae and biofilm from leaf surfaces.
Key Takeaways
- Difficulty: Moderate. Peaceful and small, but sensitive after import and vulnerable to starvation in new or overly clean aquariums.
- Minimum tank size: 15 gallons for a group of 6; 20 gallons or larger is preferred because it provides more grazing surface and stable water quality.
Habitat
Natural Habitat: Shallow, slow-to-moderately flowing streams, marginal zones, flooded vegetation, and river edges with abundant aquatic plants, roots, stones, and algae-covered surfaces.
Natural Water Conditions: Clean, oxygen-rich freshwater that is usually soft to moderately hard and slightly acidic to neutral. For O. vittatus: about 68-77°F (20-25°C), pH 6.0-7.5, and 2-18 dGH.
Other Habitat Notes: Otocinclus gather in groups around vegetation and submerged surfaces where sunlight supports algae, diatoms, and microbial biofilm.
Aquarium
Tank Size Notes: A tank with abundant surface area and established growth is more important than bare volume alone. A mature 20-gallon-long aquarium generally supports a group better than a newly set-up or sterile tank.
Tank Shape: A standard rectangular aquarium with broad horizontal surface area
Substrate: Fine sand or smooth gravel; avoid sharp materials that may damage the mouth or belly.
Plants: Use abundant live plants with broad and fine leaves. Anubias, Amazon swords, Cryptocoryne, Java fern, Vallisneria, and floating plants provide grazing and shelter.
Hardscape: Smooth driftwood, rounded stones, and other algae- and biofilm-growing surfaces
Hiding Places: Dense plants, shaded spaces under wood, and quiet areas away from active tank mates
Swimming Space: Provide open routes between planted grazing areas; they need surface access more than a large open-water zone.
Water Flow: Gentle to moderate with good oxygenation; include calmer resting areas.
Lighting: Moderate lighting that supports plant, algae, and biofilm growth. Avoid keeping every surface completely sterile.
Lid Required: Recommended. They can move quickly when startled and may reach openings near filter equipment.
Other Setup Notes: Introduce only to a fully cycled, mature aquarium, ideally at least several months old. Keep ammonia and nitrite at 0 ppm, nitrate low, and dissolved oxygen high. Never rely on visible algae as the only food source.
Behavior
General Behavior: Gentle, busy grazers that attach to leaves, glass, wood, and stones with a suction-cup mouth. They alternate between resting and short movements to new feeding surfaces.
Aggression: None under normal conditions
Territorial: No
Schooling/Social Behavior: They are gregarious and often rest, feed, or move together. Isolated fish may become withdrawn and stressed.
Group Requirements: Keep at least 6, but only add a larger group if the aquarium has sufficient grazing area and supplemental food. Similar-looking trade species usually coexist peacefully.
Notable Behaviors: They may dart to the surface and swallow air; facultative air breathing can occur in the genus. Persistent surface trips combined with rapid breathing can still indicate low oxygen or poor water quality and should be investigated.
Frequently Asked Questions
How many otocinclus should be kept together?
Keep at least 6 because they are social fish. A larger group can be even more natural, but only if the mature aquarium has enough grazing surface, supplemental food, and filtration to support everyone.
Sources and Further Reading
- FishBase taxonomy and species context: Otocinclus vittatus aquarium-trade scope FishBase Consortium