Big mark on firefish

[patrickstar]

I have a firefish in a tank with no other fish so far. I'm fighting off ich in my tank and so far it's going good. Today I found a big mark on my firefish and I have no idea what it could be.

 

[Wendy8184]

Hard to see...maybe burn from heater?

 

[Danielbdn]

He may have bruised it on a rock. Make sure you have a lid on the tank, they will jump out. I lost mine when he jumped out while I was cleaning my lid.