Swimmer, one you catch sleeping with leading lady (6)

I believe the answer is:

zander

'swimmer' is the definition.
(zander is a type of fish - something that swims)

'one you catch sleeping with leading lady' is the wordplay.
'one you catch sleeping' becomes 'Z' (as in 'catching Z's' when sleeping).
'with' becomes 'and'.
'leading lady' becomes 'ER' (Elizabeth Regina).
'z'+'and'+'er'='ZANDER'

(Another definition for zander that I've seen is " fish".)

I've seen this clue in The Times.

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