Help with Green Wolf Eel (tail has bare meat spots)

[JaMichaels]

It appears he has rubbed his scales off in certain spots nearing the end of his tail.. He shows no signs of disease and is always ready to eat.. What could I be doing wrong? This just surfaced 3 months ago, I've had him a year and a half, all water vitals are accurate.

 

[Recty]

Any crabs or anything scavengerish in the tank with him? His tail could be getting picked on.

Is he still growing? He might just be getting too big for his burrow he prefers and is starting to rub.