Slice off and discard any dark portions. In some seafood, such as abalone, the dark portions are considered a delicacy but the flavor is quite potent. In fish such as tuna, the dark portions are blood vessels and are best avoided. Use a very sharp knife to slice the fish along the grain in a motion downward and toward you. Avoid sawing the fish.
Arrange fish slices on a plate.
Layer fish and arrange into patterns or roll slices into small rosettes. Serve with a bowl of rice and soy sauce. All fish, including ocean fish, may contain parasites. The fish can then be thawed and used as sushi or sashimi. Inc. How things get done.