For as long as I can remember, there has been total confusion as to which fish is the true Corydoras aeneus. However, we’re going to try to shed some light on which of the many Corydoras aeneus variants is the true one.
The Bronze Cory and the dozen or so of its variants are spread all over the South American continent, from Colombia in the north-west to the south-eastern areas of Brazil and north-eastern Argentina.
The original type specimen was described from the island of Trinidad, which lies about 10 miles off the northern coast of Venezuela.
At various points in the past, and up to around 10,000 years ago, the island was connected to mainland Venezuela; this was during periods when sea levels were far lower than they are today.
Because of this, it would be reasonable to assume that the species of C. aeneus found in Venezuela would be genetically closest to the type specimen from Trinidad.
It is also more than enough time for allopatric speciation to occur in the divided populations, that is, they may have evolved to take full advantage of their individual environments. However, whether the forms found on Trinidad and those in nearby Venezuela are naturally compatible still needs to be proven.
Specimens and species
However, there are more than one species of so-called ‘aeneus’ that has been found in Venezuela – in fact, there are at least three. The first one closely resembles the specimens found on Trinidad in color, size, and shape.
The second species is known in the hobby as C. aeneus ‘Black’ and this fish is a similar, but more elongated, species with a very dark brown to the black evenly colored body, and deep reddish-brown fins. This may very well represent a distinct species in its own right, but further scientific examination will be needed.
The third species from Venezuela that I, along with many other Corydoras enthusiasts, consider to be a valid species in its own right is Corydoras venezuelanus Ihering, 1911.
This is a relatively small species attaining a maximum standard length (SL = body length) of 5cm/2” for females; males are smaller at 4-4.5cm SL.
It has a distinctive body shape, which differs from all other so-called C. aeneus variants.
The head is shorter with a rounded profile, the body is also shorter and this, too, has a more rounded profile. The color pattern of this species is also quite distinctive and is closer to that of C. eques than it is to C. aeneus.
A greyish mask covers the head and upper snout; there is a large distinctive red-orange patch above and behind the eye, and a large dark greyish ovate blotch, which covers the entire center of the body below the dorsal fin. The dorsal, adipose and caudal fins are reddish-brown.
Another species that I consider to be a distinct one comes from as far away from the type locality of C. aeneus as you can get.
It was originally described from the Rio Piracicaba in the state of Sao Paulo, Brazil, and was described as C. macrosteus Regan, 1912. Nijssen and Isbrücker placed it in synonymy in 1980.
Specimens for the aquarium trade are being collected from the Rio Parana in the Corrientes area of north-eastern Argentina. This is the area of Argentina which extends northward between Paraguay and Uruguay, and borders Brazil in the north, close to the area where the type specimen was collected.
This is also one of the larger variants, reaching 7.5cm/2.75” SL with deep robust body shape. The dark central body blotch extends from the gill cover to the caudal peduncle and is more or less a broad tapering band.
Another C. aeneus variant that I feel should be regarded as a true species is the one known in the hobby as C. aeneus ‘Schultzei.’ Holly described it as C. schultzei in 1940.
The type specimens were, unfortunately, lost during World War II and the type location details are not known, which makes verification of this extremely difficult.
The fish we see in the hobby come from Colombia/Peru and are another of the larger variants reaching 7cm/2½” SL for adult females, males a little less at 6.5cm”.
It has a very distinctive feature in its color pattern that pretty much separates it from all other variants.
This is in the form of a narrow, arched golden stripe, which runs from a point just above and behind the eye, curving up and along the back to the caudal peduncle.
Some exporters have called this species the ‘Golden arcuatus’ in an apparent attempt to improve sales.
All for one…?
Having looked at some of the potentially valid species from this group, we can now encompass other C. aeneus types. From my point of view, I find it very difficult to comprehend that many of these fish are actually all one and the same species, especially when you consider the facts.
Many of them may be similar in regard to their color pattern and body shape, but most have been collected from totally unconnected river systems or at least river systems that have not been linked for thousands – perhaps millions – of years.
Species such as the one which shows a golden ear flash from the Rio Itenez in Bolivia, or the other plain one from the Rio Paraguai in Paraguay, plus there are types from Rondônia in Central Brazil, Belém in eastern Brazil, Suriname and Guiana in the north, and Ecuador and Peru in the west.
To add yet another twist to the tale, there are three more so-called ‘aeneus’ variants that are all exported from Peru – the precise locations where these species are found is not known except to the people who actually collect and export them.
They are the most beautiful members of the group, although I am totally convinced that they are distinct species and not closely related to C. aeneus at all.
The first of these is the one known in the hobby as the ‘Peru green stripe’ or ‘Green laser’.
This, like the C. aeneus ‘Black’, is a slim-bodied fish with a dark upper body having a brilliant iridescent green stripe running the full length of the upper body; the fins are a light olive green.
The second of these species is very similar in shape: the body colour is a little lighter, but it possesses an equally brilliant golden yellow stripe and has a golden/olive colour to the fins. These are known as ‘Gold lasers’ in the hobby.
The final one is a species which is more typically C. aeneus in body shape and colour, although generally darker, but the striking feature of this fish is a bright red, almost straight, streak which extends from above and slightly behind the eye across the upped back, fading out as it nears with the adipose fin.
When these species first arrived in the hobby, it was thought that they were dyed or even injected fish.
However, once hobbyists started to breed them, it soon became obvious that they were indeed natural color patterns because the colors were showing true in the resulting fry.
The one thing that was apparent was the fact that these species were far more difficult to breed than the so-called normal C. aeneus.
Having said all this, between the hobbyist with dedicated breeding programs and scientists with more detailed examinations of type material, we may eventually resolve the ‘aeneus’ problem.
– Guest post by Ian Clarke