Fish with a musical tail (4)

I believe the answer is:

coda

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

I can't explain the rest of the clue.

(Other definitions for coda that I've seen before include "Final passage" , "Ending of musical piece" , "Closing part of a musical composition" , "Concluding section" , "finale in Beethoven?" .)

I've seen this clue in The Sun, The Mirror and The Daily Express.

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