Green’s Dictionary of Slang

1. looking ill, esp. around the eyes, after a drinking session.

1737		B. Franklin ‘Drinkers Dict.’ in Pennsylvania Gazette 6 Jan. in AS XII:2 91: They come to be well understood to signify plainly that A MAN IS DRUNK. [...] He’s Fishey.
1852		F. Smedley Lewis Arundel 97: They are all more or less drunk, by the fishy expression of their optics.
1856		Mons. Merlin 18 Oct. 6/2: Should he [drink] to excess [...] the next morning finds him ‘fishy’ or ‘fowsty about the gills’.
1868		letter to Editor Daily News 25 Sept. in Franklyn (1960) 176: No more tight than we were, wasn’t he? [...] then what made him so precious fishy about the gills, if he hadn’t been out on the batter the night before?
1899		letter in Dly Times (New Brunswick, NJ) 7 Oct. 5/3: I was again feeling ‘fishy.’ But i was not the only one, for about one third of the lot [of hungover sailors] were in the same fix.
1927		W. Edge Main Stem 87: Oh! hell, you always look fishy-eyed when I talk about the revolution.

2. in fig. use of sense 1, unhappy, dissatisfied.

1868		Sportsman 2/1: Notes on News [...] So much more heinous in the at present very ‘fishy’ eye of the law is the robbing of one’s grandmother.
1895		Coburg Leader (Vic.) 6 July 1/6: Some of the boys looked very fishy as Alf walked up to get that trophy he so nobly won.
1937		(con. WW1) E.C. Parsons Great Adventure 61: It [i.e. faked ‘crash landing’] got so prevalent that the brass hats began to regard even the legitimate breakdowns with a fishy eye.