Harry one returning boat for fish (7)
I believe the answer is:
halibut
'fish' is the definition.
(halibut is a kind of fish)
'harry one returning boat' is the wordplay.
'harry' becomes 'hal' (Hal can be a nickname for Harry or Henry).
'one' becomes 'i' (Roman numeral).
'returning' is a reversal indicator.
'boat' becomes 'tub' (tub could historically mean a small boat).
'tub' written backwards gives 'but'.
'hal'+'i'+'but'='HALIBUT'
'for' acts as a link.
(Other definitions for halibut that I've seen before include "Large flatfish, tasty to eat" , "Something fishy here" , "Large edible flatfish" , "Large flatfish used as food" , "Largest flatfish" .)