Smoked fish on Sunday, captain? (7)
I believe the answer is:
skipper
'captain?' is the definition.
('skipper' can be a synonym of 'captain')
'smoked fish on sunday' is the wordplay.
'smoked fish' becomes 'kipper' (I've seen this before).
'on' is a charade indicator (letters next to each other).
'sunday' becomes 's'.
'kipper' after 's' is 'SKIPPER'.
(Other definitions for skipper that I've seen before include "Captain - one using a rope" , "team leader" , "Trawler boss" , "Senior pilot" , "Captain of team or boat - type of butterfly" .)