The Collaborative International Dictionary of English v.0.48:

greenling \greenling\ n. [1400-1450]
   any spiny-finned food fish of the northern Pacific coasts, of
   the genus Hexagrammos.
   [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Pollack \Pol"lack\, n. [Cf. G. & D. pollack, and Gael. pollag a
   little pool, a sort of fish.] (Zool.)
   (a) A marine gadoid food fish of Europe (Pollachius
       virens). Called also greenfish, greenling, lait,
       leet, lob, lythe, and whiting pollack.
   (b) The American pollock; the coalfish.
       [1913 Webster]

WordNet (r) 3.0 (2006):

greenling
    n 1: food fish of the northern Pacific