12-14-2012, 11:32 AM
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Jackie's point is well taken; we sometimes get tripped up over meanings. Shoaling fish, which applies to all corys, means that the fish must be in a group because in their habitat they live in groups and are programmed by natural selection to require this. The more the better. But they do not necessarily swim around the tank as a group; some species do this more often than others. Most will do this when stressed. Spawning activity brings them together in groups. But the important point as others mentioned is having several of the species in the tank, or several of mixed species. They know they are there, and that settles them.
To your specific issue, this is perhaps due to the move. Corydoras do not like being netted and moved, this is highly stressful and I have noticed that some fish will take weeks to recover from a simple move from one tank to another. They are skittish by nature, as anyone who has ever seen them in their habitat can attest. So give them time; keep them comfy with no unnecessary interference, and they should be fine.