The Collaborative International Dictionary of English v.0.48:

Capelin \Cape"lin\, n. [Cf. F. capelan, caplan.] (Zool.)
   Either of two small marine fishes formerly classified in the
   family Salmonid[ae], now within the smelt family
   Osmeridae: Mallotus villosus, very abundant on the coasts
   of Greenland, Iceland, Newfoundland, and Alaska; or Mallotus
   catervarius, found in the North Pacific. The Atlantic
   variety has been used as a bait for the cod. [Written also
   capelan and caplin.]
   [1913 Webster + PJC]

   Note: This fish, which is like a smelt, is called by the
         Spaniards anchova, and by the Portuguese capelina.
         However the anchovy used as a food is a different
         fish. --Fisheries of U. S. (1884).
         [1913 Webster + PJC]

WordNet (r) 3.0 (2006):

capelin
    n 1: very small northern fish; forage for sea birds and marine
         mammals and other fishes [syn: capelin, capelan,
         caplin]