Captain did not start fish (6)
I believe the answer is:
kipper
'fish' is the definition.
(type of fish)
'captain did not start' is the wordplay.
'captain' becomes 'skipper' ('skipper' can be a synonym of 'captain').
'did not start' means to remove the first letter.
'skipper' with its first letter taken away is 'KIPPER'.
(Other definitions for kipper that I've seen before include "Smoked fish" , "One not awake" , "Preserved herring" , "Cured fish (one having forty winks?)" , "being in bed?" .)