Otocinclus affinis

Adults reach a length of approximately 5 cm. Sexual dimorphism in this species is weakly expressed; determining the sex is difficult, although females may be slightly larger than males. Outwardly, Otoincley affinis is very similar to its close relative — the Dwarf Otocinclus, and is often sold under the same name. The coloration is dark, with a contrasting white belly. A narrow golden horizontal stripe runs from the head to the caudal fin. A distinctive feature is the structure of its mouth, perfectly adapted for scraping algae. It resembles a sucker, allowing the catfish to firmly hold onto the surface of plant leaves.

The natural habitat of this species is in South America, near Rio de Janeiro in Brazil. Here it inhabits shallow tributaries of large rivers, as well as floodplain lakes. The fish prefers areas with abundant aquatic vegetation or dense grassy thickets along the banks.

Otocinclus affinis catfish exhibit friendly behavior: they can live both alone and in groups, and no intraspecific conflicts are observed among them. They are peaceful species and get along well with most other non-aggressive fish of comparable size. These catfish are also completely harmless to freshwater shrimp.

Otocinclus affinis does not have special maintenance requirements, provided it has enough plant food. For a small group of these fish, the optimal aquarium volume starts from 40 liters. The setup should include an abundance of plants, including those with broad leaves, which will serve as resting places for the catfish. Natural snags are also highly recommended, as mentioned earlier, because they provide a base for algae growth. To recreate conditions close to their natural habitat, oak leaves or Indian almond leaves can be added to the aquarium. Gradually decomposing, they release tannins, which give the water a characteristic tea-like tint. These substances are believed to have a beneficial effect on fish health, suppressing the development of pathogenic bacteria and organisms. It should be noted that heavily planted aquariums require special lighting regimes. In such cases, it is advisable to consult with specialists. Care can be simplified by choosing undemanding mosses and ferns, which often look no less impressive but do not require such meticulous care. Maintaining stable water parameters is crucial for the balance of the aquarium's biological system. Filtration also plays an important role. In small tanks with few inhabitants, simple air-driven sponge filters will suffice. In other cases, external filters may be required. Internal filters that create strong currents are not recommended. Essential maintenance procedures include weekly partial water changes (15–20% of the total volume) with fresh water and regular removal of organic waste.

As already mentioned, the diet of these fish is based on algae. However, acclimatized individuals can successfully feed on dry vegetable foods, such as spirulina flakes. It is important to remember that the aquarium must provide conditions for algae growth, otherwise the catfish risks going hungry. Excellent places for their development are natural snags illuminated by bright light. As an additional food source, blanched peas, small pieces of zucchini, cucumbers, and other vegetables can be offered.

At present, successful breeding of this species in home aquariums has not been recorded. The main supply of fish comes from commercial fish farms located in Eastern Europe. In the American continents, individuals caught directly in the wild are common.

The main cause of most diseases in these fish is unsuitable keeping conditions and poor-quality nutrition. If initial symptoms are observed, it is first necessary to check water parameters and the concentration of dangerous substances such as ammonia, nitrites, and nitrates. If the indicators deviate from the norm, they should be brought back into order, and only then should treatment begin.

When choosing otocinclus, pay attention to their appearance and plumpness. A healthy fish should have a rounded belly, not a sunken one, which often indicates prolonged starvation and emaciation, from which these catfish recover with difficulty. Avoid specimens with signs of damage, ulcers, or frayed scales. — Choose fish that actively scrape growths from decorations or aquarium glass, rather than those that lie sluggishly on the bottom or near the water surface. — Keep in mind that other species of otocinclus are often sold under the name M. affinis in the trade, as the true species is rarely available. — After purchase, ensure the fish has a gradual adaptation to water parameters, as this species is sensitive to sudden changes in chemical composition and levels of nitrogenous compounds.