What is this on my yellow coris wrasse?

I noticed this afternoon what appears to be a wound under the flesh? You can clearly see it from the side but head on it blends in so it's not an open or flesh wound? There's no aggression and he's eating and acting fine so it doesn't appear to be bothering him.

Could it be a burn from burrowing under the sand at night? I'm using 2mm sand and I've read people using larger grains without any problems. I started treating with Paraguard just in case. Does anyone have any ideas of what it might be?

TIA