Well almost a new fishy for me

So having some store credit at the LFS I was going to pick up a new fish today. My choices are limited to a clown or a royal gramma and already having a clown I was going to pick up the gramma. I get to the store, check out the fish, looks healthy and then it turns its head and I notice a growth on the gills, so no new fish for me. I'm not really sure what the growth is from, it looked like it was coming from the inside of the gills and was protuding out and growing down the side of the fish, maybe about half a pea in size. No skin discoloration or anything, just a growth, anyone know what that could be. The LFS isn't really prepared at all or capable of treating sw fish IMO so if I could help them out, that would be great. They only have one sw tank and they have someone come in to take care of it.

 

Fluke or isopod.

Jack