Baraminology of Callichthyidae

Baraminology of Callichthyidae

Callichthyidae is a family of freshwater catfishes well known to freshwater aquarists as containing the popular genus Corydoras. However, many members of the family are kept in home aquariums and have devoted followings among aquarists. Because they are fish and thus were not on the Ark, Callichthyidae has not been studied by baraminologists in any meaningful way. This article will examine this unique family of catfishes and attempt to determine how many distinct baramins are contained within Callichthyidae.

Callichthyidae contains two subfamilies, Callichthyinae and Corydoradinae.  There are nine genera within the two subfamilies, but most are very species poor, with one, Brochis, being monospecific, and several others such as Dianema, Hoplosternum, Callichthys, and Megalechis having less than five species.  According to evolutionary phylogenies, Callichthyidae is part of superfamily Loricarioidea. Therefore, members of that superfamily will be used as an outgroup cognitively and genetically when and if this is required.

Hybrid data for Callichthyidae is sorely lacking in the secular peer reviewed literature. There is some information within the aquarist community that points to some hybridization between some species. For example, one website claims that there are hybrids between Corydoras aeneus and Corydoras undulates[1]. Under the enhanced cognitum model of baraminology, breeding between members of the same genera is expected.  Therefore, it is expected that, given the opportunity, members of the vast Corydoras genus would breed together, or at least that their eggs could be successfully fertilized and mature by another member of the genus.

Absent hybrid data, we must apply cognitive groupings to determine which genera group together to form a baramin.  In this instance, the two subfamilies strongly group together within the subfamilies.  Subfamily Corydoradinae contains Aspidoras, Brochis, Corydoras, and Scleromystax. All four of these genera share similar traits. Like all catfish, they have sensitive organs called barbels that branch like large hairs from their chins. In this subfamily, the barbels originate in the upper jaw and point largely downward and rarely, if ever are raised to be on an intersecting plane with the body.  Their body is covered with two layers of bony scutes that intersect in the middle of the body, creating a visual line down the body.  In this subfamily, tail shape is slightly lobed, like most other fish. In most species, the dorsal fin is pronounced and pointed, with a small adipose fin set a short distance in front of the base of the caudal fin.  The mouth extends slightly from the face and points ventrally, towards the substrate, where they like to scavenge for food.  This gives them the vague appearance of a tapir with its face. The body tends to taper slightly towards the tail.  Corydoradinae tend to spawn in open water, allowing their eggs to sink and attach to rocks, sand or whatever else is beneath them.

Subfamily Callichthyinae consists of numerous small genera including Callichthys, Hoplosternum, Lepthoplosternum, Megalechis, and Dianema. The structure of the caudal fin is very different. Instead of the slight lobe of Corydoradinae, the Callichthyinae have a very squared off caudal fin. The mouth is either slightly ventral or neutral in location. The barbels are larger and point largely on a parallel plane as the body.  The dorsal fin is much less pointed, instead more closely resembling a sail in appearance.  Unlike Corydoradinae, Callichthyinae build bubble nests of air bubbles and bits of plants.  Most Corydoradinae do not care for their young and are known by aquarists to eat their own eggs. Callichthyinae are noted for their care for their newly hatched young. Based on the differences delineated here, it would appear that Callichthyidae is composed of at least two separate baramin. Lepthoplosternum, Megalechis, and Dianema could potentially be separated into their own baramin, as their bodies do taper towards the caudal fin, unlike the rest of the subfamily. They also have downward pointed barbels, and their mouths are more extended from their bodies than the rest of Callichthyinae.

While little genetic data exists outside of mitochondrial DNA for these groups, what little exists does seem to point to a discontinuity.  Based on the enhanced cognitum model, it is expected members of the same baramin will have around 95% or higher whole genome similarity. The RAG1 and RAG2 genes in Callichthys callichthys and Corydoras cf. trilineatus demonstrate 87.68% similarity[2].  A different sample looking just at the RAG2 gene found no significant similarity between C. callichthys  and Corydoras aeneus[3]. However, when Corydoras aeneus and Corydoras panda were compared using the same sequence, they were 95% similar[4]. An examination of a different set of sequences of the RAG2 gene revealed a mere 86% similarity between Corydoras ourstigma and Hoplosternum littorale[5]. The RAG1 gene demonstrates 93.8% similarity between Aspidoras taurus and Corydoras britskii[6]. This is a very small pair of sequences (less than 800 base pairs) so the similarity being slightly less than 95% is not terribly worrying for members of the same baramin.

This sample is incredibly limited.  Whole genome similarity is much preferred to partial sequences of genes. However, the little available data does seem to indicate at least that Corydoradinae is its own distinct baramin.  Callichthyinae is much less clear. There are similarities, but there are also some potential differences, as mentioned above.  Tentatively, I’ve opted to split Callichthyinae into two baramins, though should better data become available and require it, I will happily fold the two together.  Based on the information presented above,  the Corydoradinae remains intact as its own baramin, containing Aspidoras, Brochis, Corydoras, and Scleromystax. Callichthyinae will continue to house Hoplosternum and Callichthys while a third group Dianeminae houses the remaining three genera: Lepthoplosternum, Megalechis, and Dianema, for which is was named. Note that due to their being multiple baramins within Callichthyidae,  the outgroup of Loricarioidea was not used.

This arrangement is somewhat borne out by evolutionary phylogenies. One study linked Aspidoras, Brochis, and Corydoras together as a group[7].  A second study confirmed this, and postulated that Hoplosternum and Callichthys were closely related, as were Lepthoplosternum, and Megalechis[8]. While this study did place Dianema apart from the rest of its postulated baramin, it is interesting that aspects of the baraminology are being accidentally supported by evolutionary scientists.

 

References

[1] Scotcat “Corydoras undulates” Accessed April 24, 2019 https://www.scotcat.com/callichthyidae/c_undulatus.htm

 

[2] Accession #s DQ492437.1  and DQ492436.1

[3] Accession #s KP960357.1 and KP960360.1

[4] Accession #s KP960362.1 for C. panda

[5] Accession #s GQ225447.1 and GQ225475.1

[6] Accession #s GU208882.1and GU208883.1

[7] Marcelo R. Britto. “Phylogeny of the subfamily Corydoradinae Hoedeman, 1952 (Siluriformes: Callichthyidae), with a definition of its genera.” Proceedings of the Academy of Natural Sciences in Philadelphia (2003) https://bioone.org/journals/Proceedings-of-the-Academy-of-Natural-Sciences-of-Philadelphia/volume-153/issue-1/0097-3157(2003)153[0119:POTSCH]2.0.CO;2/Phylogeny-of-the-subfamily-Corydoradinae-a-classinternal-link-hrefi0097-3157/10.1635/0097-3157(2003)153[0119:POTSCH]2.0.CO;2.short

[8] Cristiane Kioko Shimabukuro-Dias, Claudio Oliveira, Roberto E. Reis and Fausto Foresti. “Molecular phylogeny of the armored catfish family Callichthyidae (Ostariophysi, Siluriformes).” Molecular Phylogenetics and Evolution Volume 32, no.1  (2004) Pages 152-163. https://www.sciencedirect.com/science/article/pii/S1055790303004226

 

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