Marinating raw fish, such as finely sliced salmon, trout, sea bass, or tuna in an acidic marinade, such as lemon or lime, will basically "cook" the fish (known as ceviche). Uncooked vegetables also benefit from being marinated. You can also use raw marinades as a base for salad dressings. Make sure your fish is very fresh.
There are many variations that can be used, as long as the base is citrus. Try these with scallops, sea bass, trout, or turbot:
Marinating technique - this step by step method will suit most firm fresh fish.

Tuna, sea bass and salmon.

Swordfish, tuna, and sea bass.

Swordfish, scallops, sea bass and tuna.
Step 1: Place all the ingredients for the marinade in a shallow bowl.
Step 2: Slice your fish fillet paper-thin, making sure all the bones have been removed.
Step 3: Add the fish to the marinade of your choice, making sure it is well covered.
Step 4: Stir it occasionally to make sure all the fish is marinating. Leave for 30 minutes to 1 hour in the refrigerator, until the fish has turned opaque.
Step 5: Remove with a slotted spoon, and transfer to a serving plate. Serve with a squeeze of lemon or lime, and a fresh leaf salad.
Note: Put the fish in the freezer for 10 minutes before slicing it paper-thin. This will firm it up, and make slicing much easier.