What white fish can be used in rolled sushi?
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.