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Hisonotus aky (Azpelicueta, Casciotta, Almirón & Koerber, 2004)

t is the month of October 2018 and the topic is a small member of the Loricariidae family and one of the most stunning discoveries of the last 14 years namely the "Green Oto" Hisonotus aky. This fish caused quite a stir in the hobby when first described and all these years later it has now been bred in the hobby.

Hisonotus aky


Hisonotus aky (Azpelicueta, Casciotta, Almirón & Körber, 2004) was originally described in Epactionotus Reis & Schaefer, 1998 because of its supposed possession of three synapomorphies proposed for that genus: neural spine of seventh vertebra not contacting nuchal plate dorsally (contacting unpaired predorsal plates), first dorsal proximal radial contacting the eighth vertebral centrum, and absence of an expanded fleshy flap on the dorsal surface of the first pelvic-fin ray in males. Also, Hisonotus aky possesses one of the additional diagnostic characters of Epactionotus: longitudinal light stripes on dorsal surface of head. However, the examination of type specimens of Epactionotus aky indicates the absence of most diagnostic features for the genus.



Hisonotus aky - three day old fry


Hisonotus aky - three day old fry


This species has been bred by English aquarist Paul Dixon from the Bolton Museum, England and is shown above.


According to Evers et al, they are only found in a small area in the Rio Uruguay drainage in the Fortaleza Creek, close to the city of Paraiso.


A very unique species, in that it can be easily recognised by its overall green body colour, although freshly imported specimens are often olive coloured and do not show the bright metallic green colouring until well settled.




The following summary is from AZPELLICUETA et al (2004). Epactionotus (Hisonotus) aky is diagnosed by the following combination of characters: 1) 21 to 23 lateral plates; 2) light stripes extended from snout tip to supraoccipital level; 3) caudal fin with dark vertical stripes; 4) ventral surface of body completely covered by small platelets; 5) 1-4 feeble serrae on distal portion of pectoral spine posterior margin.

Green body colouration although freshly imported specimens are often olive coloured and do not show the bright metallic green colouring until well settled.

Aquarium Care

They rest on aquatic vegetation in the aquarium and the less light in the tank the darker they become. Provide a current in your tank for this species as they come from swift flowing waters. A sandy substrate is best with smooth rocks and pieces of bogwood, with thickets of broad-leaved plants such as Amazon swords.



Peaceful fish with other companions who like water movement in the aquaria.

They lay their eggs on plant leaves

Sexual differences
Females grow a bit larger than the males. The males usually are not as strong in colouration and have longer fins.


Will feed on flake, algae, tablet foods, algae wafers and insect based foods.

Glossary of Terms

Lateral: A sensory line, along the sides of the body.
Nuchal: Area between the skull and dorsal fin.
Dorsal: The primary rayed fin(s) on top of the body.
Pelvic fins: The paired fins, between the pectorals and the anal fins. (also referred to as ventrals).
Supraoccipital: Unpaired bone at the back of the skull, usually with a crest.
Caudal fin: The tail.
Pectorals: The paired fins just behind the head.


Hisnotus: Greek, isos = equal + Greek, noton = back


Evers, H.-G. & I.Seidel: Mergus, Baensch Catfish Atlas Volume 1, 1st English edn., 2005. Pp.944.
Ferraris, C.J. Jr., 2007. Checklist of catfishes, recent and fossil (Osteichthyes: Siluriformes), and catalogue of siluriform primary types. Zootaxa 1418:1-628.
Azpellicueta, Casciotta, Almiron, & S. Korber, 2004, A new species of Otothyrini (Siluriformes: Loricariidae: Hypoptopomatinae) from the Río Uruguay basin, Argentina.
Tiago Pinto Carvalho; The species of Hisonotus (Siluriformes: Loricariidae: Hypoptopomatinae) of the Rio Uruguay basin, southeastern South America in: A new species of Hisonotus (Siluriformes: Loricariidae: Hypoptopomatinae) from the Laguna dos Patos Basin, Southern Brazil.

Fuller, Ian. https://www.practicalfishkeeping.co.uk/features/articles/green-oto-epactionotus-aky

Photo Credits


Top: © Ingo Seidel @ Aqua-Global

Bottom: © Paul Dixon @Bolton Museum and Aquarium










Factsheet 268

Epactionotus aky
Common Name:
Green Oto


Argentina: Yabotí-Guazú basin, Uruguay River system, Misiones. Type locality: Argentina, Misiones, Río Uruguay basin, Arroyo Garibaldi (26º38'46.1"S, 53º59'55"W).
4.5cm. (1¾ins)
18-24°c (63-75°f.)
6.5 -7.2.
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                                                                                                            Factsheet 268 = updated September 26, 2018 , © ScotCat 1997-2018  Go to Top