A born swimmer fond of fish (5)

I believe the answer is:

otter

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'a born swimmer' is the definition.
'otter' can be an answer for 'swimmer' (animal which swims). I'm unsure of the 'a born' bit.

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

Can you help me to learn more?

(Other definitions for otter that I've seen before include "Semi-aquatic mammal" , "Aquatic weasel-like mammal" , "fish-eater displayed" , "Fish eater of the weasel family" , "Mammal, 'Tarka'" .)

I've seen this clue in the Evening Standard.

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