Hi Aquarius
I just had a situation where I could observe my corys interacting together under what was really overcrowded conditions. My bronze corys had spawned (again
) and that made 3 of my tanks taken up with fry and most of my corys crowded together in one 10 gallon tank.
During this time they were all very active and playful. Some of the time they formed groups based on their variety and other times they just milled around together. This group was composed of a mixture of 6 different kinds of cory with ages from mature to juvenile. Of the 6 kinds, 2 were the only ones of their kind, yet they interacted with the others in a very natural way.
Now that they have been relocated and are again in normal numbers, they are still acting the same, although they seem a little bit more sedate most of the time. I was just watching a mixed group of albino C aeneus and green-golds playing together. (While the pandas are staying in the cave.)
I think that corys will be happy if they live in mixed groups, but I think that they seem to enjoy their own kind, too. Perhaps your solution is to keep pairs, with two or more pairs being better than only one pair.
But, I don't think you would be doing any harm if you mixed them up, either.