This is kind of unexpected, looking at the close up of the Oto’s mouth above… they appear to be actually eating some of the wood… this is a well seasoned stick, in the tank ( the one I apply Repashi to, once every week or two ) you can see the lighter spots on the stick, where they have eaten the darker seasoned surface off… I’ve had Pleco’s that actually ate wood before, but all have had visible teeth… these Oto’s appear to have the normal “bristlely” lips