Do you know what is wrong with my True Perc?

[Craiger]

I''ve had the little guy for a month (actually she's paired up) and just recently I noticed what looks like a little chunk missing right where the body and the tail meet (at the top). Don't think she was bitten. Are they susceptible to a disease that would look like this?

Any help appreciated. Don't know what to do:(

[BTTRFLYGRL]

If its the smaller of the two Clowns [the male] maybe the female got a little aggressive with him? Any other aggressive fish in the tank? Any crabs?

Its hard to say without seeing it but for now just keep an eye out for infection. Hopefully with good water conditions it will clear up on its own. If no, you may need to remove him to a qt and treat with an antibiotic