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Nematogenys inermis (Guichenot, 1848)

thought to myself, lets have something really weird for the August 2018 factsheet and here it is the only member of the Nematogenyidae family and a Chilean catfish to boot the "Mountain Catfish" Nematogenys inermis.


Nematogenys inermis = dorsal head view

Nematogenys inermis
= dorsal head view


Containing only this single species, N. inermis. The genus is endemic to some rivers in Chile. The common name for this species is "Mountain Catfish". Previously in the Trichomycteridae family and is very rare in the aquatic hobby. There was a fossil which was found and described from the Miocene, continental fluviolacustrine deposits of the upper Cura–Mallín Formation (37–39°S), Chile (Azpelicueta & Rubilar, 1997). That species was named as Nematogenys cuivi.





Nematogenys inermis =
ventral head view




N. inermis has no adipose fin and and the caudal fin is short and rounded.




Nematogenys inermis = Line drawing by W. S. Atkinson from Eigenmann 1927: Pl VII



This species is considered very primitive, mainly because it has three pairs of barbels, opercula and subopérculos without thorns, thorns of the pectoral fin and dorsal fin a level of the pelvics. However, studies have shown the reduction of the jaws that they support the chins and specialication in the loss of bones like the opisthotic, subopercular, interopercular.

Currently, N. inermis, is a species whose distribution and abundance is in frank decrease. The main reasons for its reduction are the direct alteration of its habitat by decrease of flows, dredging, channeling, fragmentation, alteration of regimes of flow, sedimentation, deforestation of the riparian zone and pollution. It is also very vulnerable to predation by introduced species.

In its native Chile its common name is "Catfish" or "Big Catfish".




Flattened head dorsoventrally. Dorsally, a longitudinal groove is seen between both halves of the epiaxial musculature and the body thins notoriously towards the caudal region. They present a wide mouth with small teeth in large quantity. They have three pairs of barbels; maxilla, nasal and mental. The eyes are small in size and separated by ample space interorbital. They have only one dorsal fin, with a narrow base and inserted over the pelvics. The anal fin is distant from the anus and separated from the pelvics. The tail fin is large and rounded. This species also has a large caudal peduncle compressed, tall and thickened dorsal rim (Ruiz, 1993).

The colouration exhibited by this fish is yellowish to light brown in the body, with a large amount of irregular spots, especially on the fins, the belly becomes clearer on the back (Ruiz, 1993).

Aquarium Care

There is not much information on keeping this species in the aquarium but as it was a former member of the Trichomycteridae family then the husbandry pertaining to this would adhere but studies indicate that in captivity they do not accept any kind of food, dying after months.



As above

An aspect of its reproduction indicates that it belongs to the category of partial synchronism, it is to say, will spawn once a season. The spawning period would occur in late spring or at the beginning of summer (Manríquez et al ., 1984).

Sexual differences
Not reported.

The feeding items for this species are basically benthic. Studies indicate that in captivity does not accept any kind of food, dying after months (Manríquez et al ., 1982). According to Oliver (1949), these fish feed at night, worms and insects. The examined stomach content reveals that the most frequent item is Hemiptera, followed in importance by Amphipoda and Diptera (chironomidae).

Glossary of Terms

Maxillary: Pertaining to the upper jaw. (maxillary barbels)
Nasal: On top of the head, by the nostrils. (nasal barbels)
Mental: Pertaining to the chin, on the lower jaw. (mental barbels)
Dorsal fin: The primary rayed fin(s) on top of the body
Anal fin: The median, unpaired, ventrally located fin that lies behind the anus, usually on the posterior half of the fish.
Pelvic fins: The paired fins, between the pectorals and the anal fins. (also referred to as ventrals)
Caudal peduncle: The narrow part of a fish's body to which the caudal or tail fin is attached.
Caudal fin: The tail.
Adipose fin: Fleshy finlike projection without rays, behind the rayed dorsal fin.
Opisthure: The tip of the vertebral column which protrudes beyond the caudal fin.
Subocular: Beneath the eye.
: Between the preoperculum and the operculum, sometimes very small, and in some Loricariidae bearing spines.


Nematogenys : Greek, nema, -atos = filament + Greek, genys, -yos = face, jaw


de Pínna, M.C.C., 2003. Nematogenyidae (mountain catfishes). p. 268-269. In R.E. Reis, S.O. Kullander and C.J. Ferraris, Jr. (eds.) Checklist of the Freshwater Fishes of South and Central America. Porto Alegre: EDIPUCRS, Brasil.
Froese, R. and D. Pauly. Editors. 2017.FishBase. World Wide Web electronic publication. www.fishbase.org, ( 02/2017 )
Ferraris, C.J. Jr., 2007. Checklist of catfishes, recent and fossil (Osteichthyes: Siluriformes), and catalogue of siluriform primary types. Zootaxa 1418:1-628.
Burgess, W.E. 1989 An atlas of freshwater and marine catfishes. A preliminary survey of the Siluriformes. T.F.H. Publications, Inc., Neptune City, New Jersey (USA). 784 p.

Photo Credits

First and second: © Iván Valdebenito Isler
Bottom: W. S. Atkinson from Eigenmann 1927: Pl VII


Factsheet 266

Trichomycterus inermis, Nematogenys nigricans, Nematogenys pallidus
Common Name:
Mountain Catfish


South America: Isolated localities in Concepción, Rancagua and Angol, Chile. Formerly widespread throughout much of Central Chile. Type locality: Chile.
24cm (9¾ins)
18-24°C (63-75°F)
6.7 -7.2.
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                                                                                                            Factsheet 266 = updated December 14, 2018 , © ScotCat 1997-2018  Go to Top