05-17-2010, 08:19 PM
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"Rocks" to me suggest sharp edges so that is probably the cause in your case. Smooth rocks have no impact, be it sand, gravel or pebbles, provided they are smooth; it is the rough edges that cause the trouble, not the gravel.
A second cause is biological. Some authors cite high nitrate levels, since these usually indicate deteriorating water conditions. I suspect it is the state of the water, which involves mainly the "health" of the water (ammonia/nitrite/nitrate and non-fluctuation conditions) plus to some extent the parameters (pH and hardness).
Lastly I have had some corys lose their barbels while all the others in the same tank for years do not. This suggests it may also be a "fish" thing, by which I do not necessarily mean a particular species per say but some species may have a more susceptible reaction to something than others. I have maintained numerous species of Corydoras for 20 years and I find C. sterbai particularly susceptible.
And, they can live for years (normal life spans) without barbels, and no, they do not grow back.