SablefishAs SSwordfish correctly stated, Black Cod, also known as Sablefish is the most common species called Butterfish on Menus.
It is Roy's biggest seller and for good reason, it's an amazing tasting fish.
However, I have seen Escolar subbed for it, which is a tradegy and a bathroom visit waiting to happen.
Calling Black Cod Butterfish started in Hawaii and made it's way to the mainland mainstream about 10-12 years ago.
Black Cod is to the North Pole what Chilean Sea Bass is to the South Pole.
It's caught in the north pacific from Northern Cali, all the way to southeastern Alaska.
The biggest ones only get to about 10 lbs H&G and the seaon runs parallel to Halibut (basically March-Nov)
It is very flaky and can be messy on a char grill so most chefs will marinate in Miso or something similar for a couple days to firm it up.
It's also been MSC Certified this past year as sustainable and well managed fishery. (Sidenote, I'm not bought in to that whole MSC b.s. but that's a whole different post.
As previously posted by someone, there is also a true Northern Hemisphere Butterfish but it is small and boney.
In the Southern Hemisphere (mainly off NZ), there is a species known as Antartic Butterfish, also known as Bluenose. A friend of mine down there flies about 3000 lbs a week fresh into LA.
It eats very similar to a very fresh Black Grouper from the gulf, but has a little more fat in the meat because of the cold water.
So, that's my first post here.
The Cat Man