The list of mercury toxicity effects are endless as it's believed to be the 2nd most toxic element known to man. It also accumulates in your body. If you guys don't want to be consuming excessive amounts of it, then I'd advise you to stay away from larger predatory fish like Tuna, Grouper, Shark, Swordfish, and even Snapper. The higher up the food chain, the higher the mercury levels become. We can thank pollution for that. Freshwater fish is OK as far as I know. You only have to go as far as researching Minamata's disease to know that this isn't something to be messing around with. A marine biology researcher did a study on this stuff using himself as the guinea pig (kind of like McDonald's "SuperSize Me") but using Tuna instead and measuring the amount of mercury in his system. Needless to say, the sushi loving people involved in the experiment didn't have the nerve to see it through the full month b/c the levels were bordering on Mimamata proportion..... enough so to scare these people off large predatory fish for life. It's also believed by many that the mercury in the amalgam fillings in your teeth cause serious health problems over the years as the mercury gradually accumulates in your system. When we chew or grind our teeth we can "supposedly" release the vapor form of mercury which we then take into our lungs..... or inhale up through our nasal passages (allowing easier access to our brains). Take it as you will, but the correlation that I've found supports the claim despite what dentists and the govt will have you believe.
Birds that do not typicxally have fish on their local dinner menu are also showing up with elevated mercury levels. Also note that organo mercury posioning is become almost common place and the main threat there is either medical labs or primarily fluorescent light bulbs.
