Arnold's Otocinclus (Otocinclus arnoldi) Care Guide
Otocinclus arnoldi is a small dwarf suckermouth catfish from the lower Paraná and Río de la Plata, a peaceful shoaling algae grazer for mature, planted tanks.
Compiled by Aquairi from published sources · Published · Updated
Overview
Otocinclus arnoldi is a dwarf suckermouth catfish of the family Loricariidae (subfamily Hypoptopomatinae). FishBase lists a maximum standard length of about 4.8 cm.
Taxonomy
- Family: Loricariidae
- Scientific name: Otocinclus arnoldi
- Subfamily: Hypoptopomatinae
- Common synonyms: Arnold Oto
Habitat
FishBase records the species from the lower río Paraná drainage, the lower and middle río Uruguai, and the río de la Plata. Otos are diurnal shoalers of small streams and well-oxygenated river margins, grazing the film on wood, stones and broad-leaved plants, and possess an air-breathing adaptation.
Tank requirements
- Minimum tank volume: 60 L (16 gal)
- Adult size: 3-4 cm (1.2-1.6 in)
- Temperature: 24-28 °C (75-82 °F)
- pH: 6-7.5
- GH: 2-12 °dGH
- Group size: ≥6 individuals
- Lifespan: 8-12 years
Diet
The diet is algae-based, dominated by diatoms and aufwuchs. The fish does best in a mature, planted aquarium with a steady supply of soft green algae and biofilm, supplemented by blanched vegetables and algae wafers. Animal foods are a minor part of the diet.
Compatibility
A peaceful species easily outcompeted for food, it requires calm tankmates. It is a social shoaler best kept in groups of at least six and is plant-safe, suiting communities of small tetras and Corydoras.
Breeding
In keeping with the genus, it lays adhesive eggs that are not guarded, depositing them on plants and aquarium surfaces.
Conservation status
The IUCN Red List assessed the species as Least Concern (2020).
Breeding Otocinclus arnoldi
Overview
Otocinclus arnoldi is a dwarf suckermouth catfish in the family Loricariidae and a shoaling algae and aufwuchs grazer. Unlike many other loricariids, in which the male builds and guards a nest, Otocinclus lay adhesive eggs and do not guard them. The genus ranges through lowlands from northern Venezuela to northern Argentina but is generally absent from the Amazon and Orinoco lowlands, and the fish primarily feed on algae or aufwuchs on roots, stones, macrophytes and broad-leaved grasses. Species-specific spawning records for O. arnoldi are very limited, so the pattern below is drawn from genus-level documentation.
Sexing
Sexual dimorphism is subtle. Viewed from above, mature females appear broader in the body than males. No reliable external colour differences are reported for the genus.
Conditioning
These fish feed almost entirely on algae and other green matter. Conditioning depends on a mature tank with plentiful biofilm and soft algae plus supplementary vegetable foods, while keeping a shoal of six or more to allow a compatible pair to form.
Spawning Behavior & Trigger
Spawning resembles Corydoras: the pair adopts the classic 'T' position, with the male holding the female between his pectoral fin and her body as eggs and sperm are released. Large weekly water changes with cooler water appear to be an important trigger, and the presence of another breeding species (Corydoras are often cited) may help stimulate activity.
Egg & Fry Care
The eggs are scattered fairly randomly, usually among plants in the upper part of the tank or on the glass; they are adhesive and receive no parental care. The fry are very tiny and require access to copious amounts of algae and other green matter once free-swimming.
Common Challenges
Otocinclus are difficult to breed in captivity, and most specimens in the trade are wild-caught. Establishing a mature algae-rich system, sexing and pairing the fish, and feeding the minute fry are the principal hurdles.