Captain loses head with swimmer who is likely to be cured (6)
I believe the answer is:
kipper
'swimmer who is likely to be cured' is the definition.
'kipper' can be an answer for 'swimmer' (type of fish). I'm not sure about the remainder of the definition.
'captain loses head' is the wordplay.
'captain' becomes 'skipper' ('skipper' can be a synonym of 'captain').
'loses head' means to remove the first letter.
'skipper' with its initial letter removed is 'KIPPER'.
'with' acts as a link.
Can you help me to learn more?
(Other definitions for kipper that I've seen before include "Smoked split herring" , "Narcoleptic" , "Cured fish (one having forty winks?)" , "One yet to wake" , "One smoked" .)