Otocinclus Catfish Otocinclus spp.

Description

Otocinclus Catfish

Otocinclus spp.

Species Background

Ottos are small South American loricariid catfish native to slow-moving tributaries and flooded forest margins of the Amazon, Orinoco, and Paraná river systems. They inhabit plant-dense, oxygen-rich waters where they spend nearly all daylight hours grazing biofilm from leaves, wood, and hard surfaces. Most Otocinclus in the aquarium trade are wild-collected, which explains both their sensitivity during acclimation and their strong preference for mature, stable aquariums.

Behavior and Temperament

Otocinclus are exceptionally peaceful and non-territorial. They show no aggression toward tankmates and do not compete through dominance or intimidation. These fish are social and should always be kept in groups, where they display calm, natural grazing behavior. Rather than darting around the tank, they methodically patrol surfaces like tiny custodians on a quiet shift.

Adult Size

Adults typically reach 1.5 to 2 inches.

Water Parameters

Stability matters more than chasing exact numbers.

• Temperature: 72–78°F
• pH: 6.0–7.6
• GH: 1–12 dGH
• KH: 0–6 dKH

Tank-acclimated Otocinclus tolerate neutral and moderately hard water as long as conditions are consistent and oxygen levels remain high.

Diet

Otocinclus are true algae and biofilm specialists, not scavengers. They require constant access to natural grazing surfaces and should never be added to sterile or newly set up tanks. While they consume soft algae and biofilm continuously, supplemental feeding is essential, especially in clean or high-maintenance aquariums.

Suitable foods include:
• Blanched zucchini, spinach, or green beans
• Soft algae wafers or spirulina-based foods
• Gel or powdered foods that adhere to surfaces

Starvation is the most common cause of loss with this species, not disease.

Tank Requirements

• Minimum tank size: 10 gallons, larger preferred for groups
• Keep in groups of 4–6 or more
• Mature aquarium with established biofilm
• Live plants, wood, and hardscape are essential
• Gentle flow with strong oxygenation

Otocinclus should not be added to brand-new tanks.

Compatibility

Compatible with small, peaceful community fish such as tetras, rasboras, danios, and dwarf gourami. Fully shrimp-safe. They do not harass fish, fry, or invertebrates and coexist well in planted and shrimp-focused aquariums.

Why They’re Popular

Ounce for ounce, Otocinclus are among the most effective algae eaters in the aquarium hobby. They specialize in grazing algae and biofilm all day long and do not transition into scavenging or opportunistic feeding. Healthy Otocinclus will not harm baby shrimp, making them one of the safest and most reliable algae-control fish for planted and nano aquariums.

Put plainly: these fish do one job, they do it constantly, and they do it without causing problems.