Slice the fish of your choice into bite sized pieces. Put a little wasabi on one side of the fish. Moisten your hands with water and place a small ball of sushi rice in your palm, about 2 tablespoons. Press the fish, wasabi side down, onto the rice. Gently hand-sculpt and shape it into an oblong. The rice has to be tight enough to hold a shape, but loose enough to melt in your mouth.