freshwater disease ID?

[Brine]

My roomate's Exodon paradoxus seems to be missing a chunk of skin. Sorry the picture isn't the best but please tell me what it is and what the treatment might be.

[exv152]

Not sure if you've ever heard of lepidophagy, interesting behaviour and wonder if it's related.
http://en.wikipedia.org/wiki/Lepidophagy

[bergenm]

If he has multiple exodons, they are very nippy and known for taking chunks out of each other...