The Collaborative International Dictionary of English v.0.48:

Sciaenoid \Sci*ae"noid\, a. [L. sciaena a kind of fish (fr. Gr.
   ?) + -oid.] (Zool.)
   Of or pertaining to the Sciaenidae, a family of carnivorous
   marine fishes which includes the meagre (Sciaena umbra or
   Sciaena aquila), and fish of the drum and croaker
   families. The croaker is so called because it may make a
   croaking noise by use of its bladder; the Atlantic croaker
   (Micropogonias undulatus, formerly Micropogon undulatus)
   and the squeteague are a members of the croaker family, and
   the kingfish is a drum.
   [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Croaker \Croak"er\ (-?r), n.
   1. One who croaks, murmurs, grumbles, or complains
      unreasonably; one who habitually forebodes evil.
      [1913 Webster]

   2. (Zool.)
      (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.
          [1913 Webster]

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

WordNet (r) 3.0 (2006):

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