Economises with shellfish, reducing temperature? (7)

I believe the answer is:

scrimps

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'economises' is the definition.
(I've seen this in another clue)

I don't understand how the rest of the clue works.

(Other definitions for scrimps that I've seen before include "Subsists on a meagre allowance" , "Subsists on a meagre amount" , "Is sparing" .)

I've seen this clue in The Independent.

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