What remains after smoking fish (5)

I believe the answer is:

roach

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'fish' is the definition.
(roach is a kind of fish)

I cannot understand how the remainder of the clue works.

(Other definitions for roach that I've seen before include "Fresh-water food fish" , "Freshwatwer fish" , "butt" , "Silver and red freshwater fish" , "Swimmer" .)

I've seen this clue in The Times.

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