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Otocinclus arnoldi Regan, 1909

Image contributors to this species:

Haraldo Bishop (2) Stuart Brown (1)

ScotCat Sources:

Article Etymology = Genus

Other Sources:

Fishbase  Search Google  All Catfish Species Inventory  Catalog of Fishes


Relevant Information:

The two images are individuals collected in the Paraná river, in a site 4 to 5 Km (2.5 to 3 Miles) to the south from Diamante City, Argentina, by Noemí and Haroldo Bishop. Otocinclus arnoldi inhabits clear waters of the southern regions of South America so this should be taken into account with temperature values in the home aquarium. Lives in the same waters as Corydoras paleatus and shares the same colour pattern. A similar looking darker species has been imported in the past from Uruguay. Aquarium Care: Requires cool waters in the aquarium as sustained high values can be problematic for this species. A planted tank is best as it is kind to plants but will keep the algae at bay. Can be a bit territorial with other fish but do well together in groups. Diet: Algae eater, tablet foods, lettuce, flake and small live and frozen foods. Remarks: The recent paper (2010) by Lehmann, P., F. Mayer and R.E. Reis have resurrected Otocinclus arnoldi from the La Plata basin from the synonymy of O. flexilis Cope 1894 from the Rio Jacuí, Rio Grande do Sul in Brazil and is thus a species in its own right based on three distinguishing features: the possession of five branched pectoral-fin rays, the larger number of enlarged odontodes on the tip of the parieto-supraoccipital posterior process, and having the prootic involved in the contact with the hyomandibular articular condyle. This species was described from “LaPlata” based on a single aquarium specimen donated by J. P. Arnold.

Common Name:







Argentina: tributaries of the lower Río Paraná drainage, lower and middle rio Uruguai, and the Río de La Plata. Type locality:La Plata.


5.0cm. (2ins)


20-24°c (67-75°f.)




Lehmann, P., F. Mayer and R.E. Reis, 2010. Re-validation of Otocinclus arnoldi Regan and reappraisal of Otocinclus phylogeny (Siluriformes: Loricariidae). Neotrop. Ichthyol. 8(1):57-68.



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