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.
(a) A small American fish (Micropogon undulatus), of the
(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.