Swimmer's eccentric aunt (4)

I believe the answer is:

tuna

'swimmer's' is the definition.
(tuna is a type of fish)

'eccentric aunt' is the wordplay.
'eccentric' indicates an anagram.
'aunt' anagrammed gives 'TUNA'.

(Other definitions for tuna that I've seen before include "Large salt water fish" , "Large food fish" , "Large sea-fish" , "Species of fish" , "Large fish for the strange aunt" .)

I've seen this clue in the Evening Standard.

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