Green’s Dictionary of Slang

1. the mouth [Cockney pron. of trout as traaht].

1859, 1860		Hotten Dict. of Modern Sl. etc.
1873		Sl. Dict.

2. the nose [= SE snout].

1930

(con. 1914–18) Brophy & Partridge Songs and Sl. of the British Soldier.

3. (also mountain trout) a bookmaker’s tout.

1932		‘P.P.’ Rhy. Sl. 15: Tout – Salmon Trout (bookmaker).
1935		A.J. Pollock Und. Speaks n.p.: Mountain trout, a tout.
1960		J. Franklyn Dict. Rhy. Sl.

4. gout.

1932		‘P.P.’ Rhy. Sl.
a.1945		L. Payne private coll. n.p.: Gout Salmon & Trout.
1960		J. Franklyn Dict. Rhy. Sl.
1969		S.T. Kendall Up the Frog 12: I’ve bin in the ’ole Uncle Ned for a couple o’ weeks wiv a touch of the salmon trout.
1977		D. Powis Signs of Crime 199: Salmon (and trout) [...] less commonly, gout.
1984		Partridge DSUE (8th edn) 1008/1: Red Daniells writes, 1980, ‘There is even a Salmon and Trout Club, restricted to gout sufferers’.

5. stout beer.

1960		J. Franklyn Dict. Rhy. Sl.
1971		J. Jones Rhy. Cockney Sl.
2002		B. Kirkpatrick Wicked Cockney Rhy. Sl.

6. (also salmon) tobacco; thus a (hand-rolled) cigarette, esp. prison use [= snout n.² (1)].

1977		D. Powis Signs of Crime 199: Salmon (and trout) Tobacco (Snout) and less commonly, gout.
2000		J.J. Connolly Layer Cake 108: Kids of ten and twelve, smoking salmon and spitting non-stop.
2011		J.J. Connolly Viva La Madness 82: ‘No, no,’ says Mort, lighting a salmon.