Hamachi kama. Some Japanese menus translate it as yellowtail jaw. Some translate it as yellowtail neck, and others translate it as yellowtail collar. While the bulk of the fish's flesh is usually served as sushi or sashimi, the jaw is often grilled, and it deserves to be less obscure to American diners.
Fish heads (and subheads) tend to be popular among Asian diners who know that the most succulent meat can be found around the neck and cheeks of many fish. One of the great Malaysian dishes is fish head curry. There are Korean, Vietnamese, and Filipino fish head soups. The Chinese prefer their fish served whole, and the head is one of the most prized parts.
For me, yellowtail gives the best head in Japanese cuisine. I've had sake kama (salmon neck), but I find it too rich and fatty. With a hamachi kama, one digs meat out from the crevices among the cartilage, moist, rich, amazingly flavorful meat. And then there's the crispy skin on one side, and the soft, white, creamy skin on the other. It's a little work to get at all the meat, but incredibly satisfying. If you're good at it, all you'll be left with when you're done is a clean hunk of cartilage and fin.
Hamachi kama is usually listed as an appetizer, but augmented by some rice, miso soup and salad it makes a fine meal.
I've most recently eaten hamachi kama at Dai-Hachi, a new restaurant near my office, at 303 E. 56th St., just east of 2nd Avenue. My several lunches there have been pretty satisfying, so I thought I'd give them a plug.