If Ahi tuna is frozen, make sure to defrost it. You can leave in the fridge for 24hrs or submerge in the cold water for about 20 minutes. When defrosted pat-dry with a paper towel after removing it from the sealed plastic bag. Double or triple the recipe if you are serving more people. Ahi tuna serving size is 6 ounces. About Ahi Tuna: Ahi tuna is often used in raw fish dishes in Asian cuisines. While it serves as a great source of several nutrients you need for good health, packed with vitamin B, D, the protein content accounts for 50 percent of the daily value of protein, it's also slightly higher in mercury than other types of tuna. The Hawaii State Department of Health recommends limiting your servings to twice per month. Ahi is perfect if you're trying to follow a high-protein low-carbohydrate diet.