Captain in south with fish (7)
I believe the answer is:
skipper
'captain' is the definition.
(I know that skipper is a type of captain)
'south with fish' is the wordplay.
'south' becomes 's' (abbreviation).
'with' says to put letters next to each other.
'fish' becomes 'kipper' (type of fish).
's'+'kipper'='SKIPPER'
'in' acts as a link.
(Other definitions for skipper that I've seen before include "One who misses" , "girl with rope?" , "who makes short hops" , "being in charge?" , "Ship's captain (colloq.)" .)