Some interesting observations on Aspidoras Catfish (Callichthyinae, Corydoradinae)

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Aspidoras is the second most speciose genus in the family Callichthyinae, and in the sub-family Corydoradinae, with 25 recognized species (Eschmeyer, 2022). Still, a long way from the more than 200 described Corydoras species.

Corydoradinae Hoedeman currently harbours three genera, Aspidoras, Corydoras and Scleromystax, and the fish can be recognized by the combination of several features, such as: narrow frontal bones, lanceolate genital papilla in males, dorsal hypohyal present and hypobranchial 1 deep (Britto, 2003).

Aspidoras are basically somewhat smaller and more noticeably elongated by comparison to most Corydoras. They are not as commonly seen in the hobby as their close cousins, but this does seem to be changing. According to Britto (2003), Aspidoras can be distinguished from Corydoras and Scleromystax by presenting the following combination of features: (I) posterior portion of mesethmoid wide; (II) frontal fontanel reduced; (III) supraoccipital fontanel present; (IV) opercle compact; (V) ossified portion of pectoral spine strongly reduced, less than half the length of the first branched pectoral-fin ray. Britto also mentioned that Aspidoras generally presents smaller eyes than other Corydoradinae and absence of contact between the parieto-supraoccipital and the nuchal plate (except for A. belenos Britto).

All species in Aspidoras possess two diagnostic features: (1) the presence of two cranial fontanels, the posterior one in the parieto-supraoccipital and the anterior one between frontals (Nijssen & Isbrücker, 1976), and (2) the ossified portion of pectoral- and dorsal-fin spines reduced (Reis, 1998). Recently, Oliveira et al. (2017) and Tencatt & Bichuette (2017) presented an apparently exclusive feature for the genus, the presence of small laminar expansions on the base of pectoral-fin branched rays, which can be irregular and form pointed structures. Indeed, this feature was not observed in any species of the remaining genera of Callichthyidae examined (Tencatt, 2017), thus being the most incisive characteristic to recognize Aspidoras.

The genus Aspidoras was erected by Ihering (1907) to accommodate the new species Aspidoras rochai which is therefore the type species. “Type species” is the distinct species that defines the specific and unique generic, physiological and morphological characteristics that all species in the genus will share.

It was some 40 years later before another species was described in this genus, Aspidoras lakoi Miranda Ribeiro 1949. Corydoras pauciradiatus (Weitzman & Nijssen 1970) was the next species described but it was only assigned to Aspidoras by Burgess (1989), who at the same time also assigned Coyrdoras raimundi (Steindachner, 1907) to Aspidoras [see more on A. pauciradiatus below]. In 1976, nine new species were described in Aspidoras (Nijssen & Isbrucker) and another in 1980 (Nijssen & Isbrucker), and more followed from 1998 into the new millenium (Britto, 1998; Britto, 2000; Lima & Britto, 2001; Britto et al, 2002; Britto et al, 2005; Wosiacki et al, 2014; Leao et al, 2015; Oliveira et al, 2017; Tencatt & Bichuette, 2017; Tencatt et al, 2020).

Nijssen and Isbrucker (1976) carried out a review of the genus, but the most detailed review, and incorporating phylogenetic analysis, was that of Luiz Tencatt (2017) which formed his doctoral dissertation for the department of biology, Universidade Estadual de Maringá. The paper is online free of charge, and contains the description of some species and colour photos.
Tencatt-Luiz Fernando Caserta-2017-DO.pdf (aquadocs.org)

A few observations made by Dr. Tencatt may be of interest to aquarists. Considering the new diagnosis plus the currently available phylogenetic data, A. pauciradiatus and A. virgulatus are herein excluded from Aspidoras, being transferred to Corydoras and Scleromystax, respectively. Regarding the remaining species, some new synonymies are proposed: A. eurycephalus and A. taurus with A. albater; A. menezesi and A. spilotus with A. raimundi; and A. microgaleus and A. marianae with A. poecilus” (page 8).

The C- and CW-number coding system used for all genera in the subfamily Coradoridae was implemented to avoid the creation of nomina nuda by using names originated by the fishkeeping hobby for putative new species. As of 2017, there were 11 coded species of Aspidoras, C35, C36 and C37, said to be from the Araguaia river basin in Goiás, C118, C119 and C125, with locality data listed only as “Brazil”, C158, said to be from da Paz River, a tributary to the Xingu River in Pará, CW52, with unknown origin, CW119, with locality listed only as “Tocantins”, CW126, said to be from the Teles Pires River basin, and CW141, said to be from the Araguaia River basin in Mato Grosso. The examination of photographs of the specimens used to assign the codes allowed most of them to be recognized as described species (p. 118).

In general, the species within Aspidoras share a similar color pattern, characterized by a longitudinal series of dark brown or black blotches plus dark brown or black markings above and below it (p. 117).

After the examination of the cave specimens [identified as A. albater] analyzed by Secutti et al. (2011) plus additional specimens also from the Anésio-Russão cave system, and epigean specimens of the region, the holotype and four paratypes of A. albater, it was possible to refute the identification of the hypogean populations as A. albater, revealing it as a new species, which is clearly different from all congeners. Here we present the description of this cave-dwelling species of Aspidoras, the first troglobitic Callichthyidae catfish, restricted to two caves of a single cave-system from central Brazil (Tencatt & Bichuette, 2017).

Contrary to what is observed in Corydoras, that often presents pairs or trios of syntopic species with convergent or shared color patterns (see Alexandrou et al., 2011), no case of syntopy within Aspidoras was observed (p. 117). This mimicry in colour patterns is fascinating in itself, but as it is applicable to Corydoras and not Aspidoras, it is a topic for another thread.

References

Eschmeyer (2022) refers to Eschmeyer’s Catalog of Fishes maintained online by the California Academy of Sciences and edited regularly by R. Fricke, W.N. Eschmeyer, and R. Van der Laan.

Alexandrou, M.A., C. Oliveira, M. Maillard, R.A.R. McGill, J. Newton, S. Creer, and M.I. Taylor, (2011), “Competition and phylogeny determine community structure in Müllerian co-mimics,” Nature, 469, 84–89.

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, 153, pp. 119–154.

Nijssen, H. & I.J.H. Isbrücker (1976), “The South American plated catfish genus Aspidoras R. von Ihering, 1907, with descriptions of nine new species from Brazil (Pisces, Siluriformes, Callichthyidae),” Bijdragen tot de Dierkunde, 46, pp. 107-131.

Oliveira, L., A.M. Zanata, L.F.C. Tencatt, and M.R. Britto, (2017), “A new species of Aspidoras (Siluriformes: Callichthyidae) from a small coastal drainage in northeastern Brazil,” Neotropical Ichthyology, 15, e160118.

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

Secutti, S., R. Reis, and E. Trajano (2011), “Differentiating cave Aspidoras catfish from a karst area of Central Brazil, upper rio Tocantins basin (Siluriformes: Callichthyidae),” Neotropical Ichthyology 2011, No. 9, pp. 689–695.

Tencatt, Luiz Fernando Caserta (2017), “The Aspidoras Ihering, 1907 (Siluriformes: Callichthyidae) armored catfishes : a taxonomic review, with description of a new species,” Universidade Estadual de Maringá. Departamento de Biologia.

Tencatt, L.F.C. & M.E. Bichuette (2017), “Aspidoras mephisto, new species: The first troglobitic Callichthyidae (Teleostei: Siluriformes) from South America,” PLoS ONE, 12, pp. 1‒24.
 
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In day to day practical terms, Aspidoras share something with Scleromystax - they seem harder to ship. I suspect oxygen needs matter there.

I've only kept fish from this Genus once - a local guy bred hundreds and I bought some in the club auction. I loved them - like small, speedy (did I say speedy? Manic) Corys. If you see them available and you like Corys, do it. Grab them. They are great fish we can learn a lot more about.
 

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