Fish worn in the cold? (13)

I believe the answer is:

leatherjacket

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

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

(Other definitions for leatherjacket that I've seen before include "Cranefly larva" , "Lava of the crane-fly" , "Swimmer" , "Cranefly grub" , "Garden pest - crane fly larva" .)

I've seen this clue in the Sydney Morning Herald.

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