A half day after Irish ship spots unique fish (9)

I believe the answer is:

lemonsole

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'a half day after irish ship spots' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'unique fish' is the wordplay.
'unique' becomes 'lemon' (I can't explain this - if you can you should believe this answer much more).
'fish' becomes 'sole' (sole is a kind of fish).
'lemon'+'sole'='LEMONSOLE'

Can you help me to learn more?

I've seen this clue in The Irish Times.

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