Small fish for the captain (7)
I believe the answer is:
skipper
'the captain' is the definition.
('skipper' can be a synonym of 'captain')
'small fish' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'fish' becomes 'kipper' (type of fish).
's'+'kipper'='SKIPPER'
'for' acts as a link.
(Other definitions for skipper that I've seen before include "One who misses" , "girl with rope?" , "Captain - one using a rope" , "Captain of team or boat - type of butterfly" , "who makes short hops" .)