An Explanation of the Changes to the Corydoradinae taxonomy

[Byron]

Aquarists fond of cory cats [who isn’t?!] may be interested in recent and proposed changes to the taxonomical classification of this intriguing family of fishes. This question appears in threads from time to time, so I’ll offer my explanation as a guide. At the end are defined terms and references.

The catfishes are classified in the order Siluriformes. One of forty-two families in this order is the Callichthyidae; the name is derived from the Greek kallis (= beautiful) and ichthys (= fish). Hoedeman (1952) defined the family Callichthyidae as comprised of two subfamilies, Callichthyinae and Corydoradinae; the latter was comprised of the tribe Corydoradidi containing the genera Corydoras and Brochis, and the tribe Aspidoradidi holding the single genus Aspidoras. 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.

The Corydoradinae subfamily is one of the most diverse siluriform assemblages in the Neotropics, holding 90% of the species in the family (Nelson, 1994; Reis, 1998; Britto, 2003); currently there are more than 500 species recognized.

The phylogenetic analysis of Reis (1998) confirmed Hoedeman’s classification and determined that the family and both subfamilies were monophyletic. In the subfamily Corydoradinae, the genus Aspidoras was monophyletic and a sister group to the clade formed by Brochis (also monophyletic) and Corydoras which was not monophyletic.

Scleromystax

Britto (2003) found overwhelming phylogenetic support for the monophyly of the subfamily, but rejected the paraphyletic standing of Corydoras + Brochis set out by Reis (1998). He confirmed the monophyly of Aspidoras as corroborated by Reis (1998) and proposed a small monophyletic group of species assigned (at that time) to Corydoras as the sister-group of Aspidoras. Rather than synonymize this group with Aspidoras, which would fail to express the monophyly of both groups, he proposed maintaining the current concept of Aspidoras and amplifying the tribe Aspidoradini to encompass Aspidoras and its sister-group. For this purpose he resurrected the genus Scleromystax, originally erected as a sub-genus of Callichthys by Gunther in 1864. Britto’s proposed classification was thus:

Subfamily Corydoradinae Hoedeman, 1952
Tribe Aspidoradini Hoedeman, 1952

Aspidoras Ihering, 1907​

Scleromystax Gunther, 1864​

Tribe Corydoradini Hoedeman, 1952

Corydoras Lacepede, 1803​

To Scleromystax, Britto (2003) assigned the species Corydoras barbatus I & II, C. prionotus, and C. macropterus, with S. barbatus the type species. S. salmacis Britto & Reis, 2005 subsequently became the fourth species in the genus, and S. reisi Britto et al., 2016 found in the laguna dos Patos drainage (thereby extending the range of this genus further south than previously) became the fifth species. All species are endemic to small tributary streams in several coastal river basins in southern Brazil (Britto and Reis, 2005; Britto et al., 2016). There are currently eight species assigned “C” numbers awaiting description.

Brochis and Corydoras

As mentioned above, Britto (2003) found overwhelming phylogenetic support for the monophyly of the subfamily, but rejected the paraphyletic standing of Corydoras + Brochis set out by Reis (1998). Brochis became a synonym of Corydoras, which was separated into what he considered monophyletic groups. The fifth of these included Corydoras aeneus, C. zygatus, C. rabauti, C. eques, and the species previously assigned to Brochis. According to Britto (2003), two exclusive characters support the monophyly of the species currently assigned to Brochis: presence of bony plate anterior to first infraorbital (character 14) and the possession of more than ten branched dorsal-fin rays (character 57). “The genus Brochis has been broadly used in ichthyological publications and is easily recognized. However, the usage of Brochis would render Corydoras non-monophyletic. In order to overcome this problem it would be necessary to create and/or resurrect at least four genera in order to accommodate species in proximate sister-groups. Given these factors, the option adopted herein is to synonymize Brochis under Corydoras.”

Subsequent Research

The first molecular phylogeny of the family Callichthyidae was made by Shimabukuro-Dias et al. (2004) and supported Reis (1998) and Britto (2003, in press at the time) with respect to the family and subfamilies being monophyletic. Results agreed with Reis (1998) and Britto (2003) that the genera Aspidoras and Brochis were monophyletic, and the genus Corydoras is not monophyletic if Brochis is accepted as a valid genus, and Brochis should therefore be considered a synonym of Corydoras. Although only a small portion of the large genus Corydoras was analyzed, the authors note that their molecular study supports the monophyly of some species groups in the tribe Corydoradini.

Subsequent ichthyological studies on new described corydoradidae species [Shimabukuro-Dias, Oliveira & Foresti 2004; Britto, Lima & Hidalgo 2007; Britto, Wosiacki & Montag 2009; Tencatt, Vera-Alcaraz, Britto & Pavanelli 2013; Barriga Salazar 2014; Sarmiento et al. 2014; Tencatt et al. 2014; Tencatt & Pavanelli 2015; Tencatt & Evers 2016; Tencatt & Ohara 2016; Tencatt et al. 2016; DoNascimiento et al. 2017] have concurred with Britto’s (2003) basic proposal. If you search any of the species in Eschmeyer's Catalog of Fishes you will find references to all these studies.

Alexandrou et al. (2011) was the first comprehensive molecular phylogenetic study of the Corydoradinae, and identified nine major lineages. In order of time since common ancestor, these are: Lineage 1 (saddle snouted species such as C. fowleri), Lineage 2 (Aspidoras), Lineage 3 (Scleromystax), Lineage 4 (dwarfs plus some others), Lineage 5 (‘elegans’ group), Lineage 6 (C. paleatus and others), Lineage 7 (‘aeneus’ group), Lineage 8 (Brochis and species such as C. haraldschultzi; there are four sub-clades), and Lineage 9 (C. adolfoi and other short snouted species). This supports the synonymization of Brochis with Corydoras, though as the authors point out, a future revision of Corydoras would unquestionably involve the reinstatement of Brochis as a distinct genus.

In Alexandrou & Taylor (2011), the authors conclude: “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 in References 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.

Ian Fuller (Fuller & Evers, 2005) lists all described species and all coded undescribed species according to the nine distinct lineages within Corydoras.

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 composed of unrelated organisms descended from more than one ancestor.

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., Claudio Oliveira, Marjorie Maillard, Rona A. R. McGill, Jason Newton, Simon Creer & Martin I. Taylor (2011), “Competition and phylogeny determine community structure in Müllerian co-mimics,” Nature, volume 469, issue 7328, pp. 84–88.

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, Marcelo 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, 153, pp. 118-154. An abstract is online:
http/www.bioone.org/doi/abs/10.1635/0097-3157%282003%29153%5B0119%3APOTSCH%5D2.0.CO%3B2?journalCode=ansp

Britto, Marcelo R. and Roberto E. Reis (2005), “A new Scleromystax species (Siluriformes: Callichthyidae) from coastal rivers of southern Brazil,” Neotropical Ichthyology, volume 3, no. 4, pp. 481-488.

Britto, Marcelo R., C.K. Fukakusa and Luiz R. Malabarba (2016), “New Species of Scleromystax Gunther, 1864 (Siluriformes: Callichthyidae)--extending the meridional distribution of genera endemic to the Antlantic Forest,” Neotropical Ichthyology 14 (3).

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

Fuller, Ian A., and Hans-Georg Evers (2005), Identifying Corydoradinae Catfish, Ian Fuller Enterprises, Kidderminster.

Hoedeman, J.J. (1952), “Notes on the Ichthyology of Surinam (Dutch Guiana). The Catfish genera Hoplosternum and Callichthys, with key to the genera and groups of the family Callichthyidae,” Beaufortia, Zoological Museum, Amsterdam, No. 12, 12 pages.

Reis, Roberto E. (1998), “Anatomy and phylogenetic analysis of the neotropical callichthyid catfishes (Ostariophysi, Siluriformes),” Zoological Journal of the Linnean Society 124, pp. 105–168.

Shimabukuro-Dias, Cristiane Kioko, Claudio Oliveira, Roberto E. Reis and Fausto Foresti (2004), “Molecular phylogeny of the armored catfish family Callichthyidae (Ostariophysi, Siluriformes),” Molecular Phylogenetics and Evolution 32, pp. 152–163.

 

[JuiceBox52]

Thank you @Byron you continue to wow me with your knowledgeable posts even despite all you are going through

 

[GaryE]

This is an excellent overview. So much to learn, eh? It's fun.

Thank you. Forget emojis, this article was well worth words!

 

[itiwhetu]

In another ten years some scientist will produce something new, and we will do it all again. I get really bored with scientists justifying their existence by doing this sort of stuff.

 

[itiwhetu]

This annoys me so much I am going to word my response in a different way.

I am Baker. I make a loaf of bread. Someone buys that loaf of bread, takes it home and feeds their family. I get paid about 1/100 of the guy who sits in an office and decides it is important to reclassify Corydoras.

 

[GaryE]

This annoys me so much I am going to word my response in a different way.

I am Baker. I make a loaf of bread. Someone buys that loaf of bread, takes it home and feeds their family. I get paid about 1/100 of the guy who sits in an office and decides it is important to reclassify Corydoras.

You seem to have a real problem with people studying and learning.

So how do we justify research? There's more to life than bread. We looked at things in simple ways for most of our species' existence, and it gave us nice, comforting mythologies to classify things with (we've always classified - it's a human thing). We started seriously questioning only about 300 years ago, and I know people who are really mad we've done that!

The value of knowing how DNA is playing out when we look at Corys, or other fish and creatures, is that we learn about diversity. It's glorious. Fantastic. Awe inspiring. It's part of learning how our planet works, and how we work. So I think the money paid for research (and the researchers I know aren't richer than owners of good bakeries) is worth every penny and more.

If you're a person who believes one or more gods did this, then it should be just as interesting. Don't you want to know what's around you? How it got here could be debated, but what it is is still being learned.

I also like really good bread, and am actually going to be learning how to improve my baking skills this winter, once I'm cooped up by weather. Loaves and fishes - great things to learn about, and all learning is equal, to the point you want to follow it to.

 

[itiwhetu]

You seem to have a real problem with people studying and learning.

So how do we justify research? There's more to life than bread. We looked at things in simple ways for most of our species' existence, and it gave us nice, comforting mythologies to classify things with (we've always classified - it's a human thing). We started seriously questioning only about 300 years ago, and I know people who are really mad we've done that!

The value of knowing how DNA is playing out when we look at Corys, or other fish and creatures, is that we learn about diversity. It's glorious. Fantastic. Awe inspiring. It's part of learning how our planet works, and how we work. So I think the money paid for research (and the researchers I know aren't richer than owners of good bakeries) is worth every penny and more.

If you're a person who believes one or more gods did this, then it should be just as interesting. Don't you want to know what's around you? How it got here could be debated, but what it is is still being learned.

I also like really good bread, and am actually going to be learning how to improve my baking skills this winter, once I'm cooped up by weather. Loaves and fishes - great things to learn about, and all learning is equal, to the point you want to follow it to.

You are wrong there, I love science and I love people who do genuine research for the improvement of our planet, I only get frustrated with the scientists that re classify stuff that doesn't need reclassifying to justify their existence and exorbitant salary. Like I say, another one of these clowns will show up in 10 years and do it all again. So, what we have with Corydoras is just another steppingstone, and will be proven to be factual incorrect eventually.

 

[GaryE]

So, what we have with Corydoras is just another steppingstone, and will be proven to be factual incorrect eventually.

I like your steppingstine comparison, as you cross a stream stone by stone. Someone has to find and work on the path. What I see in taxonomy is stone by stone, building on a direction, and adjusting as the course of the stream shows itself. At various points, you may need a few stones, and at others, the steps forward are easy.

I haven't seen complete re-dos 10 years later, with major taxonomic studies found to be factually incorrect, at least not since the ancient magical era. Can you tell me about one?

An example is my beloved killies. Collier et al did a major DNA study, the first, 20 some odd years ago. It was fascinating what it showed, as the limit of what we can see with our eyes compared to what DNA allowed us to see was really something. The new methods and tech really broke ground. I guess you'd suggest we didn't need to know.

This work on Corys isn't the final word. Maybe one of the forum members will put in the needed years of study, gain the skill and expertise and have a go at refining aspects of this work. If so, we'll learn a little bit more about a type of life on our planet. Practical? Who knows, and maybe that doesn't matter. Maybe learning is worth something.

What's wrong with that?

Meanwhile, the paper itself, which you never discussed, is kind of interesting. As I read it, my little Scleromystax barbatus were wandering about in a tank a few feet from my computer, and they made a bit more sense. When I first got them, they were classed as Corydoras, but they are very different fish to keep. That reaction of mine is no different from your reaction - absolutely meaningless in the wide world. People are going to go on doing the good work, and learning. You might as well read it and respect it, and see what it tells you.