From The Collaborative International Dictionary of English v.0.48 [gcide]:
Fishy \Fish"y\, a.
1. Consisting of fish; fishlike; having the qualities or
taste of fish; abounding in fish. --Pope.
[1913 Webster]
2. Extravagant, like some stories about catching fish;
improbable; also, rank or foul. [Colloq.]
[1913 Webster]
From WordNet (r) 3.0 (2006) [wn]:
fishy
adj 1: of or relating to or resembling fish; "the soup had a
fishy smell"
2: not as expected; "there was something fishy about the
accident"; "up to some funny business"; "some definitely
queer goings-on"; "a shady deal"; "her motives were suspect";
"suspicious behavior" [syn: fishy, funny, shady,
suspect, suspicious]