The Collaborative International Dictionary of English v.0.48:

Gilthead \Gilt"head`\, n. (Zool.)
   A marine fish. The name is applied to two species:
   (a) The Pagrus auratus (syn. Chrysophrys auratus), a
       valuable food fish common in the Mediterranean (so named
       from its golden-colored head); -- called also giltpoll.
   (b) The Crenilabrus melops, of the British coasts; --
       called also golden maid, conner, sea partridge.
       [1913 Webster]