Green’s Dictionary of Slang

salmon n.1

(UK Und.) the drowned corpse of a wealthy person.

[UK]J. Greenwood Tag, Rag & Co. 35: They hauled a ‘salmon’ as they say [...] their haul this time was a body that besides three or four sovereigns, had a gold watch and chain in the pockets.

SE in slang uses

In compounds

salmon belly (n.) [the colour]

(US Und.) a high-denomination bill.

[US]J. Black You Can’t Win (2000) 231: The roll interests you, the outside one is what you call a ‘salmon belly.’ It is a yellowback — a big bill.
salmon canyon (n.) [equation of the female genitals with SE fish]

the female genitals.

[UK]Roger’s Profanisaurus in Viz 87 Dec. n.p.: salmon canyon n. The area beyond the beef curtains (qv); that boat crewed by the bald man (qv); fanny.

In phrases

salmon-tot retriever (n.) [Carib.E. salmon-tot, a salmon-tin + mockery of the pedigree retriever breed]

(W.I.) a mongrel, kept as a watch-dog and allowed to forage for its food.

[WI]cited in Allsopp Dict. Carib. Eng. Usage (1996).