I have been making sushi using salmon and tuna for a while, but i would like to know it there are any firm white fleshed fish that will work well in a rolled sushi paired with apple and cucumber. I tried cod but it doesn't carry a lot of flavor. I had also thought about tilapia but had never seen it served in a sushi restuarant and wasn't sure it would be suitable.
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.
Fluke in season works well
A common one is haddock and is in season pretty much year round.
This is cheating, but white tuna is delicious.
Ditto the blandness.
On the contrary, tilapia is almost always served raw at sushi bars. It is usually what you are served when you order red snapper. No joke. It is pretty tasty if you get it fresh enough.
My personal recommendation for a lighter-flesh fish would have to be yellowtail (hamachi).