Hello,
It looks like he may have caught it on something in his tank. Is there anywhere that he could have wedged it inbetween to have injured it some? This happens fairly often in tanks. They will get something stuck & yank it out to free themselves.
You can get some raw, unpasteurized honey or antibiotic ointment to put on those areas to help out. It doesn't look too bad. Is it raw?
Did that area recently shed?
Tracie