In a medium bowl, mix together mayonnaise, cilantro, fresh ginger, and fish sauce. Mix in crab, shrimp, and 1/2 cup bread crumbs. Season with salt and pepper to taste.

Place remaining 1 cup breadcrumbs on a plate or shallow bowl. Drop 1/4 of the crab mixture onto breadcrumbs, and turn to coat. Shape into a circle or oval. repeat with remaining crab mixture.

Heat oil in a heavy skillet over medium heat. Cook cakes in oil for about 5 minutes per side, or until golden brown and cooked through.