Otocinclus Arnoldi (Otocinclus arnoldi) Tiny, peaceful and incredibly hardworking, Otocinclus arnoldi is one of the finest algae-grazing catfish available for planted aquariums. Its gentle nature, compact size and constant grazing behaviour make it an excellent companion for nano aquariums and peaceful community tanks with stable, mature water conditions. Quick Facts Scientific name: Otocinclus arnoldi Common name: Otocinclus Arnoldi, Arnold's Otocinclus Current size: Approximately 2–3 cm Adult size: Approximately 4–5 cm Tank size: 40L+ recommended Difficulty: 🟡 Moderate Temperament: Extremely peaceful Minimum group: 6+ recommended Is this for you? ✔️ Perfect if: You have a mature planted aquarium with natural algae and biofilm. You want one of the safest algae-grazing fish for nano aquariums. You enjoy peaceful schooling fish with fascinating natural behaviour. You can keep them in a proper group of six or more. ❌ Avoid if: Your aquarium is newly established or still cycling. You plan to keep only one or two individuals. You keep aggressive or boisterous fish. You expect them to survive solely by cleaning the aquarium. Why choose Otocinclus arnoldi? Otocinclus arnoldi is one of the smallest catfish available in the aquarium hobby, yet it performs an important role by constantly grazing soft algae, biofilm and microorganisms from plant leaves, driftwood and aquarium glass. Their peaceful nature makes them an excellent addition to aquascapes where larger algae eaters would simply be too big. Unlike larger plecos, Otocinclus remain tiny throughout their lives and rarely disturb plants or décor. They spend much of the day moving together in loose groups, methodically cleaning surfaces while adding subtle movement to the aquarium. Although hardy once established, they should only be introduced into mature aquariums where natural grazing opportunities already exist. Stable water quality and regular supplementary feeding are the keys to long-term success. Benefits Excellent grazer of soft algae and biofilm Perfect for planted and nano aquariums Tiny adult size Completely peaceful community fish Safe with freshwater shrimp and delicate plants Interesting schooling and grazing behaviour Care made simple Temperature: 22–27°C pH: 6.0–7.5 Diet: Natural biofilm, soft algae, algae wafers, spirulina foods, blanched zucchini, cucumber and spinach Water: Very clean, stable and well oxygenated with low nitrate levels Substrate: Sand or fine gravel Setup: Dense plants, driftwood, smooth stones and established algae-covered surfaces Keep in groups of at least six to encourage natural behaviour and reduce stress. Supplement their diet once natural algae becomes limited. Pairs perfectly with Cardinal Tetras Ember Tetras Pygmy Corydoras Honey Gouramis Cherry Shrimp and other Neocaridina shrimp NTA Insight: Otocinclus are often purchased purely as algae eaters, but the healthiest fish are those introduced into mature aquariums with abundant natural biofilm already available. At NTA, we recommend adding them only after an aquarium has been running successfully for several months. Once established, they become one of the most useful and enjoyable nano catfish available. FAQ Are Otocinclus good algae eaters? Yes. They are among the best fish for controlling soft algae and biofilm in planted aquariums, although they will not remove tougher algae such as Black Beard Algae or mature hair algae. Should they be kept alone? No. Otocinclus are naturally social fish and should always be kept in groups of at least six, with larger groups providing even greater confidence and more natural behaviour. Can they live with shrimp? Absolutely. Their peaceful nature makes them one of the safest catfish to keep alongside Neocaridina and Caridina shrimp. Do they eat plants? No. Healthy Otocinclus graze on algae and biofilm growing on plant leaves without damaging the plants themselves. Why do Otocinclus sometimes struggle in new aquariums? New aquariums often lack the natural biofilm and microorganisms they depend on. Introducing them into mature, established systems greatly improves their long-term survival. Are they suitable for beginners? They can be, provided the aquarium is fully cycled, mature and stable. They are less forgiving of poor water quality than many other small community fish. How long does Otocinclus arnoldi live? With excellent water quality, proper nutrition and a stress-free environment, they commonly live between 3 and 5 years.
