Green’s Dictionary of Slang

goldfish n.3

[fig. uses of SE, i.e. the image of being trapped or isolated from the outside world in a goldfish bowl]

1. (US) the beating of a prisoner to extract a confession; also the rubber hose used in such beatings; thus see the goldfish, to suffer a beating; show the goldfish, to beat up [the prisoner is the isolated goldfish, the interrogators gather round].

[US]Hostetter & Beesley It’s a Racket! 226: GOLDFISH — Piece of rubber hose or some other instrument capable of inflicting torture but without leaving marks on the body, used for extorting confessions from criminals; e.g. ‘Feeding the Goldfish’ — obtaining a confession.
[US]J. Lait Put on the Spot 79: Here [goldfish room] detectives vented their sadistic wrath against helpless men, flagellating them with the rubber hose and pummeling them with their beefy fists. This was known as ‘seeing the goldfish’.
[US]C.R. Shaw Jack-Roller 147: Prisoners are herded and kicked and cuffed and razzed like brutes. This is called ‘showing the goldfish’ or the ‘third degree’.
[US] ‘Und. “Lingo” Brought Up-to-Date’ L.A. Times 8 Nov. K3: GOLDFISH: Third degree; a police beating.
[US]Monteleone Criminal Sl. (rev. edn).

2. (US Und.) a prisoner standing in an identification line-up.

[US]Ersine Und. and Prison Sl.
[US]A.J. Pollock Und. Speaks n.p.: Gold fish, prisoners in a police show-up.

In compounds

goldfish bowl (n.)

1. (US, also goldfish room) an interrogation room in a police station.

[US]J. Lait Put on the Spot 79: There was a small back room which was known to every crook in the city. The ‘goldfish bowl’.
[US]R. Chandler ‘Finger Man’ in Pearls Are a Nuisance (1964) 111: I’d like to get the Mex in the goldfish room with me personal.
[US]Monteleone Criminal Sl. (rev. edn).
[US]D. Dempsey ‘Lang. of Traffic Policemen’ in AS XXXVII:4 269: goldfish bowl, n. An interrogation room in a jail or detention station.

2. any small room where a discussion takes place.

[US]R. Price Ladies’ Man (1985) 113: Maybe Candy was getting back at us for goofing on his fatness in that goldfish bowl on Eighth Street.