Fish from hotel beside modern-day harbour (7)
I believe the answer is:
haddock
'fish' is the definition.
(I know that haddock is a type of fish)
'hotel beside modern-day harbour' is the wordplay.
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'beside' is a charade indicator (letters next to each other) (I've seen this in other clues).
'modern day' becomes 'AD' (AD, Anno Domini, as opposed to BC, Before Christ).
'harbour' becomes 'dock' (I've seen this before).
'h'+'ad'+'dock'='HADDOCK'
'from' acts as a link.
(Other definitions for haddock that I've seen before include "Fish, often smoked" , "White fish" , "Fish like cod but smaller" , "Swimmer" , "Popular food fish" .)