Order Siluriformes
Family Loricariidae
Subfamily Hypoptopomatinae
Genus Hisonotus
— Green Hisonotus — Hisonotus aky [Azpelicueta, Casciotta, Almiron & Koerber, 2004]. Synonym: Epactionotus aky. (English – Green Oto). It inhabits Uruguay and Argentina, in the Garibaldi and Fortaleza streams (streams with strong currents, even at the edge of waterfalls or beneath them). Males are 4 cm, females 5.5 cm. It features a striking emerald coloration. Dark spots are scattered across the body and fins, being more numerous in males. The caudal fin has dark vertical stripes. The ventral surface of the body is completely covered with small plates. Males are less green and have longer fins, especially the caudal fin.
A tropical aquarium with broad-leaved plants such as Echinodorus and intensive lighting to provide plenty of algae for food. Substrate of sand or gravel, with driftwood and smooth rocks placed on it. Adult fish adapt to prepared aquarium foods, including flakes, but it is important to provide vegetable matter. Eggs are laid on the broad leaves of plants as well as on the aquarium glass. Fry reach a length of about 3.5 cm in 60 days. pH 7.0-7.5; dH 10°; T 22-26°C.
— Niger Oto — Hisonotus leucofrenatus [Ribeiro, 1908]. Synonyms: Otocinclus, Microlepidogaster leucofrenatus. (English – Niger Oto). Southeastern Brazil. 4-5 cm. They have a slender and thin body, especially in males. Near the eyes are two small bump-like growths, which are the nostrils. The black or dark brown body features many light, horizontal, narrow stripes. The flanks are darker, and the belly is lighter. The fins are almost transparent, but individual rays have a dark brown coloration. Females are larger and wider, appearing more massive.
Suitable for small aquariums, but at least 10 liters per individual. An aquarium with dense vegetation, hiding places, and shaded areas. Lighting should not be excessive, for which floating plants can be used. Absolutely peaceful, spending the whole day scraping driftwood, rocks, glass, and leaves to find food. Best kept in small groups; in fact, they do not suffer from loneliness and do not display intraspecific aggression. Prefers water with strong movement and well oxygenated.
Herbivorous, it is advisable to supplement with vegetable food for bottom-dwelling fish and vegetables. Quite easily bred in captivity. They often spawn in a well-maintained aquarium, scattering eggs into the water. Lifespan is 3 years. pH 6.4-7.4; dH up to 16°; T 20-24°C.
— Spotted Otocinclus — Hisonotus maculipinnis [Regan, 1912]. Synonym: Otocinclus maculipinnis. South America, inhabitants of the La Plata region. 5 cm. Snout pointed. Lips extended downwards, mouth acts as a sucker. Colored in sandy tones, the back is olive, passing into a yellowish-gray color with a large number of dark spots arranged in two checkerboard stripes. Similar spots are present on the colorless fins; the ends of the caudal fin have black stripes. The male has small spines on the head and pectoral fins. Males are slimmer and smaller than females.
The sucker cleans plants of algae growth. More mobile and actively removes algae from leaves than Ancistrus species. Part of the food should be given before turning off the lights. Cannot withstand competition with other herbivorous fish. Prefer to stay in the lower water layers. The male guards and ventilates the eggs. They feel well in spacious aquariums with shaded areas and hiding places. Heat-loving, temperature should not fall below 22°C. Lives up to 5 years in the aquarium. pH 7, dH 5-20°; T 24-28°C.
— Black-tailed catfish — Hisonotus nigricauda [Boulenger, 1891]. Synonyms: Microlepidogaster, Otocinclus nigricauda. Paraná and Paraguay river basins. 5 cm.
— Patterned Hisonotus — Hisonotus notatus [Eigenmann, 1889]. Synonyms: Microlepidogaster, Hisonotus, Otocinclus notatus. Brazil, Santa Cruz, Juiz de Fora near Rio de Janeiro. 3-4 cm. pH 6.5-7.4; T 22-24°C.
— Marbled Otocinclus — Hisonotus paulinus [Regan, 1908]. Synonym: Otocinclus paulinus. (English – Marbled Otocinclus). Brazil. 4 cm. Light brown with golden dots and strokes on the body and fins. Cleans plants of algae growth. The aquarium should be well planted with vegetation; driftwood and hiding places are required. Poorly tolerates nitrogen compounds dissolved in water.
Due to the small size and peaceful nature of the otocinclus, tank mates must be chosen small and peaceful. Under no circumstances should they be kept with sucker-mouth catfish, cichlids (even small and non-predatory ones), or other algae-eating fish species. Filtration must be strong, preferably through peat; aeration and weekly water changes are required.
Identification: Genus Hisonotus.
Description of the genus Otocinclus, Otocinclus cocama.
Genus Macrotocinclus, Genus Oxyropsis, Genus Schizolecis. 
