Pollachius virens, as opposed to pollachius pollachius. I catch pollack on a reasonably regular basis in north Wales, but coalfish is rarer where I fish. Pollack is greenish, bronze or brown depending upon it's living habitat. Coalfish tends to be darker green or brown - almost black, hence the name. Pollack's lower jaw protrudes, whereas coalfish's doesn't, except maybe in exceptionally large animals. Certainly as a shore angler, I've never caught a coalfish with a protruding lower jaw.
Pollack is best served very fresh. It is a delicate flesh, and straight from the sea there's an elusive hint of pepper about it. A quick coating of flour, and then flash fry it. It needs no more than that. I find the flakes are generally thinner than other gadiforms, and compared with haddock the flesh is quite 'weak' looking.
The pollack caught commercially as 'Alaskan Pollack' is the same family (Gadidae) but a different genus (Theragra), so it's as distant from our local pollack as pollack is from Cod!