1. Heat 2 inches of oil in a heavy saucepan until it reaches 375°F.
2. Mix together the egg and ice water.
3. Gently mix in 1 cup flour, being careful not to over mix. The batter will be lumpy.
4. Coat the oysters in the remaining flour then dredge into the batter. Gently drop into the oil.
5. Fry in batches for about 2 minutes. Drain on a paper-towel lined plate. Repeat with remaining oysters.
6. While oysters are resting make a homemade ponzu sauce by whisking together soy sauce, mirin, sugar, dashi, lemon juice and lime juice.
7. To serve, fill oyster shells with ponzu sauce. Place on oyster on top and garnish with pickled ginger.
8. Serve with wasabi.
*Dashi powder is available at many grocery stores and Asian food groceries.