In my book, Aquarium Fishes of the Worldby Dr. Herbert R. Axelrod, Dr. Warren E. Burgess, Neal Pronek, Glen S. Axelrod, and David E. Boruchowitz, it says that the Corydoras Pygmaeus or Dwarf Corydoras or Pygmy Corydoras actually spend very little time on the bottom of the tank and "Contrary to the actions of its relatives, Corydoras pygmaeus swims mainly in the middle reaches of the water; it spend little time on the bottom, or at least much less than the other Corydoras." It says nothing of a warning about treating them any different concerning substrata choices. It is advisable with all catfish to use care in using extremely rough surfaces but standard aquarium gravel should not be a problem.
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I have been in the hobby for 3 years and have heard that regular gravel will hurt not only the pygmy corys, but the regular sized corys as well. I have always had my cory cats in a tank with regular gravel, and have yet to see any of them with worn down barbels.