Guide to Patagonia's Monsters & Mysterious beings

I have written a book on this intriguing subject which has just been published.
In this blog I will post excerpts and other interesting texts on this fascinating subject.

Austin Whittall

Thursday, October 15, 2009

The "Naked Minnow" or scaleless characid


weird but real animals

One characteristic of fish is having scales; however, not all fish have them, some, like Patagonia’s “naked minnow” lost them to adapt to its very peculiar habitat.

Though not a cryptid this creature is so strange and unique that I have decided to include it here among the weird creatures of Patagonia. I will post about other real Patagonian animals (some regrettably extinct) like the warrah or the Fuegian dog.

The naked minnow was discovered by Carlos Berg in the late 1800s and described by Fritz Steindachner in 1903, who named it Gymnocharacinus bergii.

The naked minnnow (in Spanish Mojarra desnuda) is a stenothermic teleost fish, a relict of bygone times, whose habitat is restricted to the headwaters of Valcheta Stream.

Stenothermic: organisms that can only live within a narrow range of temperatures. Teleosts: one of the three major groups of bony fish, most of which have scales.

Naked minnow
Naked minnow (Gymnocharacinus bergii) or scaleless characid.
By Fritz Steindachner (1903).[2]

Valcheta is a short brook which has its sources on the northern slopes of Somuncurá plateau in the Argentine province of Rio Negro. It flows only 75 km (47 mi.) before draining into a salt flat known as Laguna Curicó, in the Great Valcheta depression. Its flow is intermittent and temporary along most of its course and its discharge averages only 1,5 m3/sec (52 cu. ft./sec.).

See its location on this map, where it can be seen running diagonally above the word "Negro".

Its basin is closed (endorheic) and has no connection whatsoever with other rivers or the sea. It is fed by the little rain and snow that fall on the Somuncurá Plateau, a 25,000 km2 (9,650 sq. mi.) volcanic tableland that stands about 700 m (2,300 ft.) above the surrounding Patagonian steppe.

(See my post on a hypothetical river that may have connected Lake Nahuel Huapi region with Somuncuráa and the Atlantic Ocean in post-glacial times).

The plateau was isolated during the Ice Ages from the warmer regions to the north, and like “Noah’s Ark” it safeguarded a small group of animals -like the naked minnow- that then evolved separately from their main populations.

The minnows are small, measuring only 10 cm [4 in.] long. When young they have very tiny, soft and delicate scales which, during adulthood are reabsorbed by their skin, which acquires a spongy appearance. This loss of scales is an adaptation to the lack of predators in their habitat; they don’t need the scales to protect them.

It is a relict species from the warmer tropical climate that prevailed in Patagonia until the Andes rose and it is closely related to Tropical fish such as the piranha. It managed to survive the cold Patagonian weather thanks to Valcheta stream’s unique conditions.[1]

The stream’s sources are warm thermal springs, with a constant year round temperature of about 26°C [79°F]. The minnow lives there, in the warm headwaters and is not found downstream or, anywhere else in the world.

It is endangered and only a few thousands of them live in the stream. Salmonids (brook trout and rainbow trout) introduced into Valcheta in 1941 as well as human use of water for irrigation, are a serious threat for them. Declared a National Monument in 1994, it is being actively protected and recently nets have been set up to keep the trout out of the minnow’s habitat.


[1] Menni, R., and Gómez, S., (1995). On the habitat and isolation of Gymnocharacinus bergi (Osteichthyes: Characidae). Environmental Biology of Fishes. v.42-No.1 / 01-1995: 15-23. DOI 10.1007/BF00002346.
[2] López, H. L., Mantinian, J. E. and Ponte Gómez, J., (2008). Peces continentales de la Argentina: Iconografía. Gymnocharacinus bergii. ProBiota, FCNyM, UNLP, Serie Técnica-Didactica, La Plata, Argentina, 12: 1-19. ISSN 1515-9329.

Copyright 2009 by Austin Whittall ©

Patagonian Monsters

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