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