Description
The otocinclus is the great silent worker of the community aquarium. Discreet, brown, almost invisible pressed against the glass, but essential. It scrapes green algae before they become a problem, reaching corners no other fish can clean. It's the most reliable and most underestimated cleaner in the hobby.
One fact changes everything about how you should receive it: the vast majority of otocinclus on the market are wild-caught specimens from rivers in Peru, Colombia, and Brazil. Not captive-bred. They arrive carrying the stress of transport, and acclimation is a critical moment, not a formality.
Sexual dimorphism is subtle but visible from above: females are broader and more robust in the abdominal area, especially when gravid.
Behavior
Peaceful without exception. It doesn't compete for territory or bother any other fish. It moves mainly during the day, climbing glass, plants, and decorations with its characteristic suction-and-push movements. While it doesn't form tight schools, it prefers being near others of its species — in groups of 4+ it moves with much more confidence and hides much less.
Habitat
Otocinclus affinis inhabits moderate-current rivers and streams of southeastern Brazil, especially in the Paraná basin. It lives in shallow areas among emergent and submerged vegetation, often in groups of thousands of individuals. The water is clean, clear, and well-oxygenated — exactly the opposite of Amazonian blackwaters.
In its natural environment it grazes algae continuously. Its sucker mouth, with tiny rasping teeth in multiple rows, is optimized for removing the fine green-brown algae film from leaves, rocks, and glass without damaging the underlying surface.
Habitats
Fish sharing this habitat
These fish appear in one or more habitats linked to this profile. It doesn't mean they are directly compatible in an aquarium.
Details
🌊 Water parameters
🐠 Minimum tank size
Breeding
Egg-layer. Males persistently pursue females until they accept courtship. Eggs are deposited on clean surfaces — glass, broad plant leaves like Anubias or Cryptocoryne — in small groups of 3–6 eggs. Parents don't guard the eggs.
Breeding in the aquarium is possible and documented with some frequency in well-established aquariums, but is difficult to reproduce intentionally. Fry are very small and need biofilm and fine algae from day one.
Diet
Primarily herbivorous. Its ideal diet is the natural algae film (periphyton) that grows on glass, rocks, and plant leaves. In mature aquariums with sufficient light, it often needs no additional feeding. In clean or newly set up aquariums, supplementing is mandatory:
- Blanched vegetables (30 s in boiling water): zucchini, cucumber, carrot — secured with a clip to glass or substrate.
- Spirulina or algae wafers placed near the substrate.
- Dried Indian almond leaves (Terminalia catappa): it grazes the biofilm that grows on them.
Regularly check the belly: a healthy otocinclus has a slightly rounded belly. A sunken belly indicates hunger — an urgent warning sign.
⚠️ Copper: extremely sensitive to copper even at minimal concentrations. Never use copper-containing treatments in an aquarium with otocinclus.
What about your tank?
Enter your tank's values to see only the compatible species that fit them. Litres apply to fish.
Compatible fish
General guidance based on water parameters, behaviour and known exceptions; always review the individual animals' and aquarium's specific needs.
They share water: pH 6–7.5 and 24–26 °C.
They share water: pH 7–7.5 and 26 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 6–7.5 and 22–26 °C.
They share water: pH 6–7.5 and 22–26 °C.
They share water: pH 6–7.5 and 22–26 °C.
They share water: pH 6–7.5 and 24–26 °C.
They share water: pH 6–7 and 24–26 °C.
They share water: pH 6–7.5 and 22–26 °C.
They share water: pH 6–7.5 and 20–25 °C.
They share water: pH 6–7.5 and 24–26 °C.
They share water: pH 6.5–7.5 and 20–24 °C.
They share water: pH 7–7.5 and 20–26 °C.
They share water: pH 6.5–7.5 and 22–26 °C.
They share water: pH 6–7.5 and 25–26 °C.
They share water: pH 6–7.5 and 22–26 °C.
They share water: pH 6–7.5 and 24–26 °C.
They share water: pH 6–7.5 and 24–26 °C.
They share water: pH 6–7 and 24–26 °C.
They share water: pH 6–7 and 20–26 °C.
They share water: pH 6.5–7.2 and 22–26 °C.
They share water: pH 6–7.5 and 20–22 °C.
They share water: pH 7–7.5 and 22–26 °C.
They share water: pH 6–7 and 26 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 6–7 and 22–26 °C.
They share water: pH 6.5–7.5 and 22–26 °C.
They share water: pH 6–6.5 and 24–26 °C.
They share water: pH 6–7 and 23–26 °C.
They share water: pH 6–7.5 and 23–26 °C.
They share water: pH 6–7.5 and 20–26 °C.
They share water: pH 6–7.5 and 23–26 °C.
They share water: pH 6–7.5 and 22–26 °C.
They share water: pH 7–7.5 and 22–26 °C.
Compatible invertebrates
General guidance based on water parameters, behaviour and known exceptions; always review the individual animals' and aquarium's specific needs.
They share water: pH 7–7.5 and 20–26 °C.
They share water: pH 6–6.5 and 20–24 °C.
They share water: pH 6.5–7.5 and 22–26 °C.
They share water: pH 7–7.5 and 20–25 °C.
They share water: pH 7.5 and 24–26 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 7–7.5 and 22–26 °C.
They share water: pH 7.5 and 26 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 7–7.5 and 22–26 °C.
They share water: pH 6.5–7.5 and 20–26 °C.
They share water: pH 6–6.8 and 20–24 °C.
They share water: pH 6–6.8 and 20–24 °C.
They share water: pH 6.5–7.5 and 20–26 °C.
They share water: pH 7–7.5 and 20–26 °C.
They share water: pH 6.5–7.5 and 20–26 °C.
They share water: pH 6.5–7.5 and 20–26 °C.
They share water: pH 6.5–7.5 and 20–26 °C.
They share water: pH 6.5–7.5 and 20–26 °C.
They share water: pH 6.5–7.5 and 20–26 °C.
They share water: pH 6.5–7.5 and 20–26 °C.
They share water: pH 7–7.5 and 22–26 °C.
They share water: pH 7–7.5 and 22–26 °C.
They share water: pH 6.5–7.5 and 20–26 °C.
They share water: pH 7–7.5 and 20–26 °C.
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They share water: pH 7–7.5 and 20–26 °C.
Sources
- FishBaseFroese y Pauly (eds.), 2026. FishBase.
- Delapieve et al. (2017)An appraisal of Hypoptopomatini. Neotropical Ichthyology, 15(4): e170079.
Plan your next aquarium
Is this fish right for you? Plan a suitable aquarium before setting it up.