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Family: Loricariidae, Subfamily Hypoptopomatinae

Common Name: Oto Catfish

Origin and Habitat: Amazon River basin in Peru. Occurs close to the surface in small rivers and streams among dense marginal vegetation where the water is quiet, and on floating plant thickets.

Compatibility/Temperament: Very peaceful; can be housed in any community aquarium of non-aggressive fish. Must be kept in a group of at least three, and the aquarium should be planted [see details under Description].

Oto Catfish Diet

Vegetarian, it feeds on algae and aufwuch in its habitat. When introduced to an aquarium, there should be a good supply of common green algae or diatoms (brown algae) present or the fish may well starve. Once acclimated, it will feed from sinking foods such as algae, spirulina, kelp tablets and discs. Vegetables such as blanched spinach, cucumber and zucchini may be offered. It will eat other foods but must not be fed a diet lacking in vegetable (algae, etc) matter.


Attains close to 1.5 inches (3.5 cm).

Minimum Tank Suggestion

5 gallons.

Water parameters for Oto Catfish

Soft to medium hard (1-12 dGH), acidic to slightly basic (pH 5 to 7.5) water, temperature 21-26C/70-79F. This fish is very sensitive to varying and unstable water parameters and conditions [see additional comments under Description].


The identification of the specific species of oto in the home aquarium is not always easy as there are several with very similar patterns and the names attached to them in stores are frequently inaccurate. Fortunately the care and behaviour is basically identical whichever species you may have in your aquarium. No Otocinclus species possesses an adipose fin, but this fin is present on the species in the closely-related Paratocinclus genus.

Otocinclus macrospilus is probably the species most often encountered in the hobby; this species is often mis-identified as O. affinis [see comments below]. It is strikingly similar to O. vestitus and can be distinguished by the markings on the caudal (tail) fin. O. macrospilus has a dinstinctive large round black blotch at the base of the caudal fin; on O. vestitus the horizontal black band extends onto the caudal fin with no significant enlargement into a blotch. O. vittatus is another near-identical species, but the upper edge of the black horizontal band along the sides of the fish is bordered by a distinct white clear band separating the black band from the mottled pattern; on O. macrospilus the white band is less distinct in places and on O. vestitus the mottled pattern adjoins the black band with no definable white band. The photos below illustrate, first to last, O. macrospilus [2 photos], O. vestitus and O. vittatus respectively.

This is a shoaling fish that will usually not last long on its own or even as a pair; a group of three minimum is required, more when space allows. The aquarium should be well-planted; this species' sole activity during daylight hours is to graze algae from plant leaves, wood, rock, tank walls--indeed any surface. It will frequently stop to rest on the leaves of plants, and may frequently be inconspicuous in the aquarium. Without abundant plants and other surfaces it will feel exposed and vulnerable and such stress readily brings on health issues and early demise. There have been reports of otos feeding off the sides of certain other fish; this habit is probably the result of stress or insufficient vegetable (algae) matter in the aquarium. Otos continually eat, so this must be considered when acquiring them.

There is a high mortality rate among newly-purchased otos. This is because they are wild-caught, and upon arrival in stores are most often nearly starved; being an algae-eater, it needs regular feedings of such food. They should always only be introduced to a tank containing plants with algae [this replicates their natural habitat], either the common green algae or diatoms (brown)--these fish willnot eat algae such as brush, beard, etc. If this is not done, they may very likely starve to death quickly. Once they have eaten algae and settled in, they will quite readily find and eat sinking algae-type discs and tablets, along with fresh vegetables as mentioned under Diet. They can live in a well-planted aquarium for years and rarely even be seen except at feeding times. The writer has had them spawn in heavily-planted aquaria un-noticed until the near-mature fry were observed.

You may observe otos suddenly dart to the surface for a gulp of air, very similar to the catfish in the Callichthyidae (corys, etc) family. Otos possess a modification of the esophageal wall that may function in aerial respiration and assist in providing additional buoyancy that aids these fish in remaining close to the water surface in their habitats [Schaefer, 1997].

There are several oto species that mimic the patterning of sympatric Corydoras species. Otocinclus mimulus, O. flexilis, O. affinis and O. xakriaba are considered to be mimics of Corydoras diphyes, C. paleatus, C. nattereri and C. garbei respectively [Axenrot & Kullander, 2003]. Mimetic association means the imitation or mimicry in pattern between the two species; sympatric species are those living in the same geographical habitat.

The species was described in 1942 by C.H. Eigenmann and W.R. Allen. The genus name is derived from the Greek oto [ear] and the Latin cinclus [a latticework], referring to the holes in the head in the region of the ears.

As mentioned previously, this species is often seen under the name Otocinclus affinis. In 2001, I.J.H. Isbrucker proposed the genus Macrotocinclus for O. affinis and O. flexilis on the basis that these two species form a clade according to S.A. Schaefer's 1997 study, and the species are now listed as Macrotocinclus affinis and M. flexilis in the California Academy of Sciences database.

The genus Otocinclus was erected by Cope in 1871. In 1997, Scott A. Schaefer revised the genus, recognizing only 13 of the original 65 species; the others he re-assigned to various genera. Since then, three new species have been described as Otocinclus, bringing the genus total to 16 valid species. The phylogenetic biogeography of Otocinclus led Schaefer to suggest that much of the generic and species-level diversification of the Otocinclus and perhaps other loricariid catfishes occurred prior to the formation of the Amazon basin [Schaefer, 1997]. The phylogenetic relationships among the fish in the subfamily Hypoptopomatinae are currently under study, and the genus Otocinclus may eventually be relocated [Lehmann, 2006].


Axenrot, Thomas E. & Sven O. Kullander (2003), "Corydoras diphyes (Siluriformes: Callichthyidae) and Otocinclus mimulus (Siluriformes: Loricariidae), two new species of catfishes from Paraguay, a case of mimetic association," Icthyological Exploration of Freshwaters 14(3), pp. 249-272.

Isbrucker, I.J.H., I. Seidel, J.P. Michels, E. Schraml & A. Werner (2001), "Diagnose vierzehn neuer Gattungen der Familie Loricariidae Rafinesque, 1815 (Teleosti, Ostariophysi)," DATZ, Sonderheft Harnischwelse 2, pp. 17-24.

Lehmann, Pablo A. (2006), "Otocinclus batmani, a new species of hypoptopomatine catfish (Siluriformes: Loricariidae) from Colombia and Peru," Neotropical ichthyology, volume4, number4.

Schaefer, Scott A. (1997), "The Neotropical cascudinhos: Systematics and biogeography of the Otocinclus catfishes (Siluriformes: Loricariidae)," Proceedings of the Academy of Natural Sciences of Philadelphia, 148, pp. 1-120.

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