Otocinclus arnoldi

Otocinclus arnoldi is a species that lives in the clear waters of the lower Paraná, Uruguay and La Plata basins in Argentina, Uruguay and southern Brazil. It is one of the relatively large members of its genus; its standard length is 4–4.5 cm and its total length 5–6 cm.

Its most important difference is its temperature requirement: because it comes from the cool waters of the south, it does not stay healthy at constantly high temperatures. It is a suitable algae grazer for unheated or cool-kept planted aquariums.

• At least 60 liters for a group of 6.
• A mature, planted aquarium with established biofilm.
• 19–23°C is ideal; clean, well-oxygenated water.

Biofilm and fine algae are its main food; it should be supplemented with blanched zucchini, spirulina tablets and algae-based gel foods. Check the belly line of new arrivals; a sunken belly is a sign of starvation.

Peaceful and calm; in a group it grazes more boldly. It harms no fish or shrimp.

Good companions: Small fish that like cool water: White Cloud Mountain minnows, zebra danios, dwarf shrimp, coolwater corydoras (paleatus).

Avoid: Discus and warm-water species, large and aggressive fish.