Fish male clerk left out for cooking (8)

I believe the answer is:

mackerel

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'fish' is the definition.
(I know that mackerel is a type of fish)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for mackerel that I've seen before include "One in school" , "Spiny-finned food fish" , "Important food fish" , "Fish caught by spinner (or sprat?)" , "A fish; sort of breeze, sky" .)

I've seen this clue in The Times.

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