I just got a new goldfish the other day, and one of my friends pointed out how his gill looks likes its bruised? Wanted to see what you guys thought... If its natural or if there is something wrong with him....
It looks normal to me - some goldfish naturally have clear operculum. It doesn't have to be the same on both sides - often one side is clear and the other naturally colored. As long as it doesn't get any worse, the fish is eating well and acting normally, I wouldn't worry too much.