Smudge Spot Corydora

[Baccus]

I dont know how popular or common these guys are in the aqurium trade, but I have noticed that of the 4 I purchased a while ago 2 had large smudge areas near their tail and two had only a small smudge area near the tail. Now I have noticed another difference 2 of the smudge spots have gone very golden. I don't know if this is a common thing with them as they mature or have I somehow ended up with two either sub-species or did some one somewhere along the line hybridise these fish? If the gold is due to maturing then I think these fish make an amazing show in a peaceful community tank.

 

 
From what I can see the two smudge spots that only had the small spot area are smaller than these ones that have the large area and turned golden. Also the ones with the small smudge spot still have the silver body with no gold.
 

 

[Akasha72]

I have 3 in my tank and they seem to be very rare around these parts. I've never seen them since. Mine are only around a year old (I got them as young fish last summer so I'm guessing at their age) so I've not noticed any colour changes yet. I'll let you know if I do

 

[Byron]

The colouration and intensity can vary somewhat depending upon the fish and its environment; diet may also factor in.  There is a blueish colour to the blotch at the base of the caudal fin and the anterior part of the fish has a beautiful mauve or sometimes golden sheen that can be quite reflective of light.
 
As far as I know, this species is endemic to the Rio Jamari, a tributary of the Rio Madiera, in East Rondonia, Brazil.  If this is the case, then the species is unlikely to have evolved into different piopulations, though that cannot be ruled out.  However, all fish in the hobby are wild caught (unless one has a local breeder), and different species are highly unlikely to have evolved in such close proximity that they can be caught together.  The species epithet similis is the Latin for "looks like," a reference to the similar colouration and pattern in Corydoras ourastigma, but this latter species has a long snout whereas C. similis is rounded.  C. ourastigma is not found within the same system, but occurs in the Rio quiri and Rio Purus systems.
 
If you take a look at the photos accompanying the article on this species in Planet Catfish, you will see significant variation in the colour and pattern; the caudal blotch can vary a lot.  I have a group of seven C. similis, representing three purchases several years apart.  The last three that I acquired last year have remained pretty much identical, but within the four acquired previously (from two different sources, 6-7 years ago), there is noticeable variation.  This is not a species one finds often, nor in large numbers (likely due to the high cost) so I have had to grab what I could when I find them.
 
Byron.

 

[HarpyFishLover]

The gold-colored ones are so pretty!

 

[Baccus]

The gold colouration certianly does make them look nice and stand out, however I think it proves once and for all that they are not the same as my original mystery corys that I had bought these 4 as companions for.
One of my original unknown corys

these have no smudge at all and have a blunt nose and have stayed relatively small, even smaller than a false julii. They are also more inclined to be hidden away under the thick plants. The only similar corydoras I have been able to rule out my mystery corys as being are C. guapore, C. caudimaculatus, C. spectabilis, and C. similis
As far as I know my two mystery ones have never spawned and now that I have had them nearly 10 years its looking more unlikely that I will ever find more of them or get these two to spawn.
I tried to get some more recent photos of my mystery corys but they really are stubborn about leaving the deep dark recesses of the tank even with the bribery of food. As an example this is often all I will see of my mystery corys.



 
And then there are the smudge spots

 

[Byron]

Your "mystery" corys look very similar to three I have that were sold to me by an importer as Corydoras reticulatus.  I already had three Corydoras reticulatus and from the moment I introduced the newer three I have not been convinced they are the same species.  They are much paler, like those in your photos, compared to the much darker three I already had, and the reticulated pattern is nowhere near as obvious to me.  C. sodalis is very similar to C. reticulatus, differing by the lack of a black dorsal fin blotch; the reticulated pattern is much the same on both.
 
There are dozens of spotted cory species so pinning them down is not at all easy.  Interestingly, my six are also very "shy," and I rarely if ever see them except when feeding.
 
Byron.

 

[Baccus]

I may have narrowed down my mystery corys to C. polystictus but then most of these I have seen lack spots all the way to the back of the body while my mystery ones have spots going all the way to their tail.