Zuke is the old method to preserve fish in Japan by soaking fish fillet in soy sauce mixture. The method was almost forgotten after refrigeration system was introduced, but it started to regain popularity decades ago. The most common fish to be used for zuke is tuna, but bonito, salmon, jack mackerel are used, too. I mainly use salmon, which is relatively easy to get in the United States.
Modern zuke is just marinading thinly sliced fish fillet for 15 minutes or so only to flavor the fish. Choosing fresh salmon is extremely important. To make this recipe, buy salmon for sashimi. Don’t attempt to eat regular salmon raw. Don’t eat fish if it smells like ammonia. Fresh fish shouldn’t smell bad.
Also please note that farm raised salmon don’t have parasites but wild salmons may have them in their muscle. Parasites die when the fish is cooked or frozen. Even though you are not going to die by parasites, the extremely painful stomachache is hard to forget.
Costco occasionally sells fresh “ahi tuna.” The red meat tuna with very low oil content is not suitable for regular sushi, but it is perfect for zuke. I tried several times, and always had fantastic result.
You have to have certain amount of confidence if you are going to prepare and eat raw fish. If you have any doubt, go to a Japanese restaurant, where fresh sashimi or sushi are served.