Single port before fish (5,4)

I believe the answer is:

dover sole

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'single port before fish' is the definition.
I don't know anything about this answer so I can't tell whether this works.

'single port before fish' is the wordplay.
'single port' becomes 'dover' (English port. I am not sure about the 'single' bit.).
'before' is a charade indicator (letters next to each other).
'fish' becomes 'sole' (sole is a kind of fish).
'dover'+'sole'='DOVER SOLE'

Can you help me to learn more?

(Other definitions for dover sole that I've seen before include "Kentish flat fish" , "Catch" .)

I've seen this clue in The Daily Express.

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