Source : Webster's Revised Unabridged Dictionary (1913)

Croaker \Croak"er\ (-?r), n.
   1. One who croaks, murmurs, grumbles, or complains
      unreasonably; one who habitually forebodes evil.

   2. (Zo["o]l.)
      (a) A small American fish ({Micropogon undulatus}), of the
          Atlantic coast.
      (a) An American fresh-water fish ({Aplodinotus
          grunniens}); -- called also {drum}.
      (c) The surf fish of California.

   Note: When caught these fishes make a croaking sound; whence
         the name, which is often corrupted into crocus.

Source : WordNet®

croaker
     n 1: the lean flesh of a saltwater fish caught along Atlantic
          coast of southern U.S.
     2: any of several fishes that make a croaking noise