Otocinclus ~ Otocinclus affinis

The Otocinclus is a small, peaceful algae-grazing catfish prized for its gentle nature and exceptional ability to keep aquarium surfaces clean. Known for its sucker-mouth and streamlined body, the Otocinclus originates from the slow-moving tributaries and floodplain creeks of South America, where it lives among dense aquatic vegetation and feasts on biofilm and soft algae. Its calm behavior, diminutive size, and compatibility with community tanks make it one of the most popular choices for planted aquarium keepers.

• Size: 1.5-2 inches

• Lifespan: 3-5 years

• Temperament: Peaceful, timid

• Group/Solitary: Must be kept in groups of 4-6+

• Food: Herbivorous grazer, biofilm, soft algae, blanched vegetables, algae wafers

• Water Requirements: 72-79°F, pH 6.0-7.5, soft to moderately soft water

Otocinclus thrive in mature, heavily planted aquariums with stable water parameters and abundant natural surfaces coated in soft algae or biofilm. These fish are highly social and should always be kept in groups to reduce stress and encourage active grazing behavior. Because they rely heavily on naturally occurring microfilm, they do best in tanks that are well-established rather than newly set up. Their diet can be supported with high-quality algae wafers, spirulina-based foods, and occasional blanched vegetables such as zucchini or spinach. Consistent water changes, low nitrates, and plenty of hiding spaces help ensure long-term health.

In the wild, Otocinclus inhabit shallow, vegetated margins of rivers and streams across the Amazon and its surrounding basins. These environments are rich in submerged plants, leaf litter, and woody debris that nurture a constant supply of the soft algae they feed on. Their specialized sucker-mouth allows them to cling to leaves and stems in gentle currents while grazing without disturbing the delicate vegetation.

Fun Fact: Otocinclus have a unique behavior called “shoaling grazing,” where the entire group moves along surfaces together, scraping algae in synchronized patterns much like a tiny cleanup crew.