I noticed that one of my Juii Corydoras has lost his whiskers, properly called barbels. Other Corys in the same tank seem to be fine.
A Corydoras Catfish can wear down his barbels by digging around for food. Even though the gravel in this tank looks smooth I have read that just pushing and pushing into the gravel can eventually wear down the whiskers.
Sand is the referred substrate for Corydoras and I do use it in a few of my tanks. It’s cheap to buy Playsand at a Home Depot, Menards, Lowe’s type-store. So much cheaper than buying Aquarium Gravel.
I’m going to tear down this tank and put sand on the bottom. It seems to me that sand can be abrasive, too, but the idea is that when the Cory pushes on it, the sand moves.
Corys also need clean water. Do your water changes. If the barbels are damaged and the fish lives in dirty, bacteria-laden water it could eventually kill it. I am very guilty of being slack about this. After seeing my little Julii Cory with no barbels I am vowing to try harder.