How many otocinclus catfish should I keep?

Minimum 6; for community-tank stability and proper behavior, the high end of the range is more reliable. Solo or paired individuals of schooling species typically hide and stop displaying normal behavior.

What tank size do I need?

Realistic minimum is 20 gal long. Smaller tanks technically house the species but compress the social and territorial dynamics in ways that show up as stress over time.

What water parameters does this species prefer?

Temperature 72–79°F (22–26°C), pH 6.0–7.5, GH 4–15 dGH. Tank-bred commercial stock typically tolerates a wider range than wild-type fish, but parameters in the middle of the listed range produce the most consistent behavior.

Otocinclus Catfish Care — Tiny algae grazer. Schooling — solo otos waste awa

Scientific name

Otocinclus spp. (commonly O. vittatus, O. macrospilus)

Origin

South America (Brazil, Peru, Bolivia)

Adult size

1.5–2 in (3.8–5 cm)

Lifespan

3–5 years

Min group / structure

6 (the species starves in smaller groups)

Min tank size

20 gal long

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Overview

Otocinclus catfish are the smallest practical algae eaters in the hobby, but they have a hard ceiling on tank suitability: they need an ESTABLISHED tank (3+ months old, with visible biofilm and soft algae) before introduction. Adding otos to a sterile new tank means they starve within 2 weeks. Once established, a school of 6+ keeps glass and broad-leaf plants clean.

Behavior and group dynamics

Schooling and peaceful. Spend most of the day grazing the glass, driftwood, and plants. Below 6 fish, they fail to forage actively and waste away over 2-4 weeks. Wild-caught stock is typically stressed and parasite-loaded; tank-bred is increasingly available and dramatically more reliable.

Tank requirements

20-gallon minimum for a school of 6. Tank should be at least 3 months mature with visible biofilm. Supplement with blanched zucchini, algae wafers, and Repashy gel food during low-algae periods. Soft acidic water mirrors their native habitat but commercial stock tolerates 6.5-7.2 pH.

Temperature: 72–79°F (22–26°C).
pH: 6.0–7.5.
GH: 4–15 dGH.
Ammonia / nitrite: 0 ppm sustained.
Nitrate:< 20 ppm.

Tank mates

Compatible with:

Most peaceful community fish (tetras, rasboras, dwarf gourami)
Corydoras catfish (different niche)
Cherry shrimp
Bristlenose pleco (different surfaces — otos do glass/leaves, plecos do wood)

Avoid:

Aggressive cichlids
Large predators (angelfish, larger gouramis)
Boisterous tank mates that stress out otos and reduce foraging

Frequently asked questions

How many otocinclus catfish should I keep?: Minimum 6; for community-tank stability and proper behavior, the high end of the range is more reliable. Solo or paired individuals of schooling species typically hide and stop displaying normal behavior.
What tank size do I need?: Realistic minimum is 20 gal long. Smaller tanks technically house the species but compress the social and territorial dynamics in ways that show up as stress over time.
What water parameters does this species prefer?: Temperature 72–79°F (22–26°C), pH 6.0–7.5, GH 4–15 dGH. Tank-bred commercial stock typically tolerates a wider range than wild-type fish, but parameters in the middle of the listed range produce the most consistent behavior.

Stocking density calculator — verify community compatibility before adding otocinclus catfish.
Tank volume calculator — confirm working volume vs nominal tank size.
Cycling a new aquarium — non-negotiable before adding any fish.
Water parameters explained — context for the temp / pH / GH ranges above.

Not veterinary advice — for sick fish or tank emergencies, consult an aquatic veterinarian or a qualified local aquarium professional.

Sources: FishBase species page. Mainstream hobby references (Aquarium Co-Op, Tetra, Hagen care sheets) used for hobbyist-context framing only — not cited as anchors for numerical claims. Where sources diverged, this guide takes the conservative beginner-safe position.

Otocinclus Catfish care