The fillet has a slimy membrane covering the surface. Although once cooked, it is not too bothersome, it is best to remove most of the membrane. I used my fingers to pinch, pull up, and raise the membrane from the surface and slice it horizontally using a fillet knife. This way you could remove most of it without slicing off too much meat but you can decide if this is worth the effort. I cut the fish meat into bite sized chunks and marinate them for several hours in the refrigerator in a mixture of soy sauce, sake and mirin (2:1:1) with grated ginger. Just before cooking, I drain and pat dry with a paper towel and dredge the pieces in potato starch or "Katakuriko" 片栗粉 shaking off any excess flour. Meanwhile I heat up the peanut oil to about 170C (350F). I deep fry the fish until the surface is set and the meat is done (2-3 minutes depending on the size of the chunks).
Although I served this with green tea salt, it has enough seasoning so just lemon juice was fine. It has a nice crunch on the surface with firm texture and very nice flavor. We restrained ourselves and only enjoyed a small amount.