Fish – What exactly is “Sushi Grade” fish

White fish are, as a rule, more delicately flavored than darker fleshed fish. Add farm-raised to that equation and you have the makings for a very bland meal, which is why you almost always see farm-raised white-fleshed fish served with heavy herb treatments and powerful sauces, or (in cod's case) fry batter. Tilapia and cod are two of the most common farm-raised fish on the market, so I'm leaning heavily on my suspicion that you're trying to make sushi out of the farm-raised varieties and not wild game.

If it's white fish you desire for sushi, talk to your fishmonger. Tell him what you're doing and ask for his recommendation. He'll direct you toward game fish that that are either very new and very fresh or that of the flash-frozen variety.

Provided you go to a reputable sushi restaurant with good hygiene standards, you should have no problem in terms of bacteria or parasite-related health problems. Most fish used in sushi restaurants is flash-frozen at -20 degrees C (-4F), which kills parasites outright.

As for mercury, you can check the FDA's page detailing the amount of mercury in the various species of edible fish, to help you make an informed decision. They recommend that higher risk groups, such as pregnant women, limit their intake of certain fish to 12oz/week.

Generally, sushi is extremely healthy as it is low in fat and high in vitamins and minerals - Japan has the highest life expectancy in the world, after all: diet plays a big part in that.