Otocinclus Catfish ("Otos") 2cm

Otocinclus catfish (commonly called "Otos") are peaceful, dwarf freshwater suckermouth catfish from South America that serve as excellent algae-eating champions for planted aquariums. Growing to only 1.5 to 2 inches (4 to 5 cm), they are highly sought after because they efficiently clean surfaces without harming delicate plants, shrimp, or small fish. However, because they are mostly wild-caught and have specialized dietary needs, they require an established aquarium setup to survive and thrive long-term.

Species Overview & Behavior

Schooling Fish: They are highly social and must be kept in groups of at least 4 to 6. Keeping them alone causes severe, fatal stress.

Activity Level: Unlike many nocturnal catfish, Otos are diurnal. You will see them actively buzzing around the tank during daytime hours.

Unique Adaptation: They possess a specialized digestive tract that allows them to breathe atmospheric air if oxygen levels in the water drop.

Dietary Requirements (Crucial Care Factor)

The most common mistake hobbyists make is assuming Otos can live entirely off naturally occurring tank waste. Starvation is the leading cause of death for newly purchased Otocinclus.

Preferred Food: They specialize in eating soft green algae, brown diatoms, and organic biofilm growing on wood and leaves.

What They Avoid: They will not eat tough algae types like Black Beard Algae (BBA) or Green Spot Algae.

Supplemental Feeding: In a clean tank, they quickly run out of food. You must feed them high-quality sinking Kelp or Algae Wafers and blanched vegetables like zucchini, cucumber, or carrots. Remove any uneaten vegetables after 24 hours to keep the water clean.

Perfect Tank Mates vs. Fish to Avoid

Because they are completely defenseless, choosing the right tank mates is key.

Excellent Companions: Caridina and Neocaridina Shrimp from Aquarium Co-Op, Snails, Guppies, Neon Tetras, Harlequin Rasboras, and Corydoras catfish.

Dangerous Mates: Aggressive or large fish like Cichlids, Angels, Barbs, or large Goldfish that can easily fit an Oto into their mouth.

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