Corydoras discussion

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I have 8 albinos and 6 each of peppers and bronze (they will soon match the albino numbers) my bronze and albinos are all over each other all day but do like to play with their own kind on occasions. My peppers on the other hand do have a mingle here and there but love to be around their own kind. I find peppers are very shy where as the bronze and albino are really out there, surfing the glass and getting into mischief. Funny little critters they are
 
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I think it depends mostly on how similar/compatible they are. Some years ago (maybe 30!? :oops:) I bought a couple of cories, not knowing they needed friends (the person at the shop said they'd be fine with only 2 :rolleyes:). My dad told me otherwise, but when I went to find others of the same type, I couldn't find any. My dad gave me some cories, which he thought were compatible, but a different type. I don't remember, now what the ones I bought originally were, but I think the ones my dad gave were 'green' cories, which I think is another name for bronze cories. My cories seemed okay with their friends. At least they lived long lives there. One of them was still alive 10 years later when I gave all my fish & equipment to my brother because I was moving abroad. :)
 
I think it depends mostly on how similar/compatible they are.

This too.

My weitzmani do like to hang around my bronze (share a similar colouring) a lot and the ambiacus/leucomelas (share the black mask) group. They ignore the sterbai.

Also, some cories in the wild do mix into other shoals as well, mind you still with their own shoals. The spotted cories do this a lot. Which is why some of them get caught along with the other species and wind up in the pet trade (my ambiacus is an example). These are called by catch cories. You may find these oddballs mixed in shipments of common cories at the store.

My ambiacus was mixed with trilineatus at petsmart.


Interestingly, my albino aeneus stick with each other more than their normal counterparts. And my albino sterbai also hangs out with them over other cories too. Id be curious how my albino paleatus get along with the albinos of others, but i have them in my single shoal tanks with the rest of my paleatus and they love the normal paleatus a lot too.

It is fascinating to see how they mingle together. Id imagine weitzmani would also love pandas given how close they look. But im leery on mixing anyone with pandas because pandas will breed with anything they can! Lol
 
There is one crucial aspect of this issue that has not yet been mentioned, but before I get to that...I concur with what has been posted by some other members.

Corydoras species tend to live as conspecifics in most of their habitats, being geographically isolated; but it is not uncommon to also find two species in a geographical area. They live in groups of hundreds, and that does seem to be the significant aspect. Others have mentioned the "chum around together" behaviour of cories of different species and the chumming of members of the same species. While some species do spend more time together, given the opportunity, they do also seem to enjoy mixing company.

The dwarf species are best kept alone, as one or two other members mentioned. They do tend to form "friendships" with upper fish much more than most of the larger sized species. Corydoras hastatus is frequently seen in a shoal mixed in with a shoal of small-sized characins (tetras especially). The dwarf species also need more in the group than the larger cousins, though the larger the group the better for all of these fish. This issue of numbers really does make a difference to the well-being of the fish.

The only real negative to mixing species is hybridization, and this is the issue not yet mentioned in this thread. Someone posted the article on an aquarist in Europe maintaining species in his basement tanks that would be used to restock the habitats. It is unfortunate that we are today seeing the largest extermination of species in millions of years. Keeping the gene pool of a Corydoras species pure is crucial; it may very well soon be the case that the only living members of a species are those in aquarists' tanks.

What this means is that those of us who keep multiple species must absolutely never introduce fry into the hobby beyond our own tanks. In their habitats, there is no evidence of hybridization, and the geographical isolation I mentioned above is unlikely to result in hybridization. But there is now plenty of evidence that species within the same lineage will hybridize when placed together in the artificial confines of an aquarium. I have concrete examples of this within my own cory aquarium. But I am cognizant that these fry must never leave my tanks alive.

There are now over 160 described species, and dozens more "C" and "CW" numbered fish awaiting scientific study that may or may not turn out to be distinct species, with the polyphyletic genus Corydoras. A polyphyletic clade (here a genus) is a group of organisms (here, species) derived from more than one common evolutionary ancestor or ancestral group and therefore not suitable for placing in the same taxon. By contrast, a monophyletic clade is a group of organisms (again species here) descended from a common evolutionary ancestor or ancestral group, especially one not shared with any other group. Biological taxonomy aims to classify all species within a monophyletic genus, as this has benefits to our understanding of the species.

Phylogenetic analysis by several ichthyologists over the past few decades (subsequent to the discovery of DNA in the 1970's) have identified nine distinct lineages with the family Corydoradinae. This family includes the genera Aspidoras, Brochis, Corydoras and Scleromystax; all nine lineages are represented in the present Corydoras genus. See Britto (2003), Ferraris (2007), Tencatt et al. (2013), Barriga S. (2014), Sarmiento et al. (2014), Tencatt et al. (2014), Tencatt & Pavanelli (2015), Tencatt & Evers (2016), Tencatt & Ohara (2016), Tencatt et al. (2016), and DoNascimiento et al. (2017).
  • The genus Scleromystax initially erected as a subgenus of Callichthys by Günther (1864) and then made synonymous with Corydoras by Nijssen & Isbrücker (1980), was resurrected by Britto (2003) for Corydoras (now Scleromystax) barbatus and a couple of other species, and there are now 8 described Corydoradinae species and 8 undescribed "CW" numbers in this genus.
  • Britto (2003) synonymized the three Brochis species into Corydoras and these, along with two other Corydoras species and a few "CW" numbers, now comprise lineage 8.
  • A recent study by Luiz Tencatt (unpublished so not taxonomically "accepted" yet) of Aspidoras has proposed moving one species into Corydoras, leaving the remainder as lineage 2 (16 described and 3 undescribed species).
Species now placed within each one of these lineages are very likely to hybridize in the aquarium, something very unlikely to occur in the wild beecause of the circumstances such as those I already referenced. Responsible aquarists realize the situation here, and act accordingly; we do not need to be adding to the already overwhelming degradation of nature.

I will explain the lineages more if anyone asks.
 
There is one crucial aspect of this issue that has not yet been mentioned, but before I get to that...I concur with what has been posted by some other members.

Corydoras species tend to live as conspecifics in most of their habitats, being geographically isolated; but it is not uncommon to also find two species in a geographical area. They live in groups of hundreds, and that does seem to be the significant aspect. Others have mentioned the "chum around together" behaviour of cories of different species and the chumming of members of the same species. While some species do spend more time together, given the opportunity, they do also seem to enjoy mixing company.

The dwarf species are best kept alone, as one or two other members mentioned. They do tend to form "friendships" with upper fish much more than most of the larger sized species. Corydoras hastatus is frequently seen in a shoal mixed in with a shoal of small-sized characins (tetras especially). The dwarf species also need more in the group than the larger cousins, though the larger the group the better for all of these fish. This issue of numbers really does make a difference to the well-being of the fish.

The only real negative to mixing species is hybridization, and this is the issue not yet mentioned in this thread. Someone posted the article on an aquarist in Europe maintaining species in his basement tanks that would be used to restock the habitats. It is unfortunate that we are today seeing the largest extermination of species in millions of years. Keeping the gene pool of a Corydoras species pure is crucial; it may very well soon be the case that the only living members of a species are those in aquarists' tanks.

What this means is that those of us who keep multiple species must absolutely never introduce fry into the hobby beyond our own tanks. In their habitats, there is no evidence of hybridization, and the geographical isolation I mentioned above is unlikely to result in hybridization. But there is now plenty of evidence that species within the same lineage will hybridize when placed together in the artificial confines of an aquarium. I have concrete examples of this within my own cory aquarium. But I am cognizant that these fry must never leave my tanks alive.

There are now over 160 described species, and dozens more "C" and "CW" numbered fish awaiting scientific study that may or may not turn out to be distinct species, with the polyphyletic genus Corydoras. A polyphyletic clade (here a genus) is a group of organisms (here, species) derived from more than one common evolutionary ancestor or ancestral group and therefore not suitable for placing in the same taxon. By contrast, a monophyletic clade is a group of organisms (again species here) descended from a common evolutionary ancestor or ancestral group, especially one not shared with any other group. Biological taxonomy aims to classify all species within a monophyletic genus, as this has benefits to our understanding of the species.

Phylogenetic analysis by several ichthyologists over the past few decades (subsequent to the discovery of DNA in the 1970's) have identified nine distinct lineages with the family Corydoradinae. This family includes the genera Aspidoras, Brochis, Corydoras and Scleromystax; all nine lineages are represented in the present Corydoras genus. See Britto (2003), Ferraris (2007), Tencatt et al. (2013), Barriga S. (2014), Sarmiento et al. (2014), Tencatt et al. (2014), Tencatt & Pavanelli (2015), Tencatt & Evers (2016), Tencatt & Ohara (2016), Tencatt et al. (2016), and DoNascimiento et al. (2017).
  • The genus Scleromystax initially erected as a subgenus of Callichthys by Günther (1864) and then made synonymous with Corydoras by Nijssen & Isbrücker (1980), was resurrected by Britto (2003) for Corydoras (now Scleromystax) barbatus and a couple of other species, and there are now 8 described Corydoradinae species and 8 undescribed "CW" numbers in this genus.
  • Britto (2003) synonymized the three Brochis species into Corydoras and these, along with two other Corydoras species and a few "CW" numbers, now comprise lineage 8.
  • A recent study by Luiz Tencatt (unpublished so not taxonomically "accepted" yet) of Aspidoras has proposed moving one species into Corydoras, leaving the remainder as lineage 2 (16 described and 3 undescribed species).
Species now placed within each one of these lineages are very likely to hybridize in the aquarium, something very unlikely to occur in the wild beecause of the circumstances such as those I already referenced. Responsible aquarists realize the situation here, and act accordingly; we do not need to be adding to the already overwhelming degradation of nature.

I will explain the lineages more if anyone asks.
Would you say cories from different lineages can easily hybridize, or only those within the same one?

I know panda cories are usually the biggest culprit behind hybrids.

And interesting theres some speculation that the aeneus in the pet trade is made up of various different similar species since the true aeneus is in a location not really used for import
 
Would you say cories from different lineages can easily hybridize, or only those within the same one?

I know panda cories are usually the biggest culprit behind hybrids.

And interesting theres some speculation that the aeneus in the pet trade is made up of various different similar species since the true aeneus is in a location not really used for import

This discussion [hybridization] comes up on Corydoras World regularly, and Ian Fuller has strong views on hybridization but they are shared among the scientific community. I learn from such people, so I try to take notes, and I happen to have some on your very questions. Quotation marks are Ian's verbatim comments.

Hybridization between Corydoradinae species in nature is so rare as to be non-existant so far as we know. "In nature some species do occasionally cross, especially at a time when severe conditions bring species together that would not normally be found in the same place. This is known in science as speciating." "Hybrids in the home aquaria, or fish house/room are extremely rare, especially if the species that are kept together are in groups containing both sexes. The real problems arise when groups of single specimens of several species are kept together and conditions are favourable." Species within the same lineage is in fact species within the same genus (when that genus is monophyletic) and hybridization would be easier here. Species from different lineages is the same as species from different monophyletic genera, and that would be rare if not non-existent in nature and less likely in an aquarium especially if proper conditions are maintained as Ian mentioned above. There are several professional ichthyologists on CW, people like Hans Georg Evers, Luiz Tencatt, David Sands, etc, so there is a sort of "peer review" of what any of us posts, and agreement can be taken as representative of the scientific community.

Corydoras panda: "As far as I am aware C. panda is a solitary species in its natural location and as such has no genetic barriers that may otherwise prevent fertilisation." This explains why the species can readily spawn with so many others. C. panda is also in lineage 9 which is the most species-rich, with some 63 described species and 99 undescribed "C" or "CW" fish which may or may not all end up as distinct species.

Corydoras aeneus: "Another example and even more complicated is the so called C. aeneus. This species was described from the island of Trinidad and as such is isolated from mainland South America. Actually I believe there are two forms there on having a gold shoulder flash and the other does not, this one has a striking metallic green body colour very much like that of most Brochis species. Now on the mainland there are at least three varieties form totally unconnected regions that were originally described, C. schultzei, C. venezeulanus, and C. macrosteus, and added to these there are several undescribed species that fall into the so called "aeneus" group CW26, CW041, CW048 & CW097. So like the C. paleatus and C. longipinnis the specimens of C. aeneus that are being commercially bred could very likely be a mixture of any combination of these. So my logic says the true C. aeneus comes from Trinidad and no where else."

A very similar thing is likely relevant with Hyphessobrycon eques, the Serpae or Red Minor Tetra. This species has a very large geographic distribution, and there are variations among some of these geographic populations. It has been commercially raised for decades. I think it was Weitzman who surmised that the aquarium fish is probably far removed from the original species.
 

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