This is an impossibility, unfortunately. We must remember that as soon as we place fish in the confines of an aquarium, we are forcing them into an artificial and unnatural environment. What may occur can be something that would never occur naturally. The fish are being brought into contact with species they were never intended to meet.
With that in mind, we should assume that a species may cross-breed with another species in the same genus. However, I would suggest it may go further, since we now know that the present "Corydoras" is most probably a group of nine different genera. But these fish are still quite close in their evolution.
I see evidence of possible cross-breeding among the 50 corys in my 70g, representing 12 species. A couple weeks ago I rescued a fry from the filter during cleaning, and at this early stage it appears to be a Corydoras metae. Now, I have two of this species (all the store had) but I had assumed both are male, from their slimness, and if correct, obviously one of them has spawned with a female of another species. The fry will live out its life in my aquarium. I would never release this fish into the hobby, and that is all that matters.
Byron.
