The Collaborative International Dictionary of English v.0.48:

menhaden \men*ha"den\, n. (Zool.)
   An American marine fish (Brevoortia tyrannus) of the
   Herring family (Clupeidae), chiefly valuable for its oil
   and as a component of fertilizers; -- called also
   mossbunker, bony fish, chebog, pogy, hardhead,
   whitefish, etc.
   [1913 Webster]

WordNet (r) 3.0 (2006):

menhaden
    n 1: shad-like North American marine fishes used for fish meal
         and oil and fertilizer [syn: menhaden, Brevoortia
         tyrannis]