Taste buds aside, it's important to understand that most types of fish, if eaten in moderation, are good for you because of the omega-3s and protein they provide. However, there are definitely certain types of fish that are better than others when it comes to avoiding mercury. Fish with the least amount of mercury include salmon, flounder, oyster and crab, among others, while large fish like King Mackerel, Bigeye and Ahi Tuna and Swordfish are known to contain the highest amounts of mercury.