BTW, welcome aboard!
Here's an easyand quick brine, Costco Sesame dressing mixed with an equal part of cold water, 1 cup each to start. Put the filets of yellowtail in a gallon ziplock bag and enough of the brine to soak for 1 hour at room temperature or 4 hours in the fridge. The Yellowtail filets are lighter in flavor so they don't take that much. Put the tuna filets, which are denser and stronger flavored into another bag, fill with brine and leave over night.
Low and slow is my motto, 220 degrees for 2 hours and you are god to go!