Brochis catfish are now in Corydoras

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Byron Amazonas

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Aquarists fond of cory cats may be interested in recent (and proposed) changes to the classification of this intriguing family of fishes. There is an explanation of scientific terms at the end, and then the references with links.

The Callichthyidae [the name is derived from the Greek kallis (= beautiful) and ichthys (= fish)] is a family of catfish (the zoological order Siluriformes). There are two subfamilies, Callichthyinae and Corydoradinae. The latter holds 90% of the species, more than 170 described to date, and this is where we find all the cory-like catfish; until fairly recently, these were classified within one of three genera, Aspidoras, Brochis and Corydoras. The name of the genus Corydoras, which was erected by B.G.E. Lacepede in 1803, is derived from the Greek cory [= helmet] and doras [= skin, incorrectly used here for "armour"]; it refers to the dual row of overlapping plates (instead of scales) along the body, comparable to a suit of armour.

With the benefit of DNA this classification has been regarded as needing revision, and in 2003 M.R. Britto proposed one on the basis of his thorough phylogenetic examination of the subfamily.

Britto (2003) resurrected the genus Scleromystax and moved four cory species (C. barbatus, C. macropterus, C. prionotos, and C. lacerdai) into it. [Planet Catfish today lists eleven species in this genus, but two are actually synonymous* and the remaining five are new and as yet undescribed, being identified by a “C” number.] These species constitute a monophyletic clade, and are thus a distinct genus. Britto also revised the two tribes of the subfamily Corydoradinae. The tribe Aspidoradini, previously constituted only by the genus Aspidoras, is composed of Aspidoras and Scleromystax; the species in these two genera share traits not shared by any Corydoras. The tribe Corydoradini, which previously included the genera Brochis and Corydoras, is now composed only of the genus Corydoras.

The anatomical differences that previously separated the three Brochis species [Brochis splendens (the Emerald “Cory”), B. britskii and B. multiradiatus] from Corydoras are no longer considered sufficient to create a distinct genus given the phylogenetic analysis. These “Brochis” species belong to a clade shared by four Corydoras species, namely C. aeneus, C. zygatus, C. rabauti and C. eques . Britto (2003) consequently effected the synonymization* of Brochis with Corydoras. Ferraris (2007) followed this and moved the three Brochis species into Corydoras, and thus they are now known as Corydoras splendens, C. britskii and C. multiradiatus respectively. This classification has been accepted as valid in the California Academy of Sciences database and Fishbase.

Britto determined that the species in Corydoras, of which Fishbase lists 158 described to date, were not monophyletic and he proposed a number of taxonomic changes to this subfamily that results in nine clades, i.e., nine different genera. The afore-mentioned genus Scleromystax is one of these clades, since the species in it are monophyletic.

Subsequent ichthyological studies on new described cory species [Shimabukuro-Dias, Oliveira & Foresti, 2004; Britto, Lima & Hidalgo, 2007; Britto, Wosiacki & Montag, 2009; Tencatt, Vera-Alcaraz, Britto & Pavanelli, 2013] have concurred with Britto’s basic proposal . Alexandrou & Taylor (2011) followed Britto’s concept and have also proposed substantial revisions which include the described species and all known undescribed “C” species: “It is clear from the molecular phylogeny that the Corydoradinae are in need of taxonomic revision. The need for this revision has been recognized for some time (Isbrucker, 2001), although it is only now that the genetic relationships among species are clear, allowing species to be grouped into phylogenetically meaningful and monophyletic groups. Here we present suggestions for revision of Corydoradinae (both formally described and undescribed taxa). This is intended as an outline proposal for a future taxonomic revision, and does NOT represent a formal revision. All species should continue to be referred to as Corydoras, Aspidoras or Scleromystax until a thorough peer-reviewed revision incorporating both morphological and genetic data has been published.”

This paper is available online for no charge [see link below]. Aside from the ichthyological propositions, this study provides a comprehensive discussion around the mimicry we find in so many of the cory species. The section headed “Ecology of the Corydoradinae” is well worth a read for those wishing to explore this mimicry.

Definitions

A taxon (plural taxa) is a group of organisms given a formal taxonomic name, such as a species, a genus (which is a group of one or more species that share specific traits that are unique to those species within the genus) and a family (the genus or group of genera that share other unique characteristics that make them distinct from all others).

A monophyletic (sometimes holophyletic) taxon is one that includes the most recent common ancestor of a group of organisms, and all of its descendants; a monophyletic group constitutes a clade. A paraphyletic taxon is one that includes the most recent common ancestor, but not all of its descendants. And a polyphyletic taxon is one that does not include the common ancestor of all members of the taxon.

Mimicry is the similarity between two species, which may be in appearance, behaviours, etc.

*synonymous, synonymization: The scientific classification of all animal life on earth is governed by the Code of the International Commission of Zoological Nomenclature. Except in rare cases where other factors prevent it, the name assigned to any species must be the first name given to that species as a distinct taxon. When the genus name of a species must be changed according to new understanding, and the genus species are to be included with species from another genus, the oldest genus name predominates, and the discarded name is termed a synonym.

References

Alexandrou, Markos A. and Martin I. Taylor (2011), “Evolution, Ecology and Taxonomy of the Corydoradinae Revisited,” online at http://www.academia.edu/5890874/Evolution_ecology_and_taxonomy_of_the_Corydoradinae_revisited

Britto, M. R. (2003) “Phylogeny of the subfamily Corydoradinae Hoedeman, 1952 (Siluriformes: Callichthyidae), with a definition of its genera,” Proceedings of the Academy of Natural Sciences of Philadelphia, volume 153, pp. 119-154. An abstract is online:
http://www.bioone.org/doi/abs/10.1635/0097-3157(2003)153[0119:POTSCH]2.0.CO;2?journalCode=ansp

Ferraris, C.J.Jr, (2007), “Checklist of catfishes, recent and fossil (Osteichthyes: Siluriformes), and catalogue of siluriform primary types,” Zootaxa, No. 1418, pp. 1-628. Online: http://www.mapress.com/zootaxa/2007f/zt01418p300.pdf
 
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Hey, I was just talking to my husband about how similar Brochis splendens and Corydoras aeneus looked. I was shocked that they weren't even in the same genus! Shows what I know! Didn't realize they were re-arranging the taxonomy. Thanks for the informative post. It's really interesting to see the things that are getting re-classified now that we have access to DNA sequencing and testing. :)
 
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