Fish tails caused by something other than copper?

Mine do this in the summer. I think it has to do with them laying on the packed dirt, or in the barn on the plywood floor and switching at flies !! They end up beating the hair off the end of their tails.

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Read it here in the past couple months. As I recall the idea was the worms caused a general poor condition and loss of hair at the tip was a sign of that. I;m still new to the copper idea and am reading up on it.