Fish-eater adding large scale to exhaust (7)

I believe the answer is:

dolphin

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

I don't understand the rest of the clue.

(Other definitions for dolphin that I've seen before include "Sea mammal like large porpoise, friendly towards people" , "Bottlenose creature?" , "Small sociable whale" , "Sociable sea mammal, sacred in ancient Greece" , "Marine mammal with an elongated beak-like head" .)

I've seen this clue in The Daily Express.

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