He’s caught the carp, is prepared to stuff it (6)
I believe the answer is:
captor
'he's caught the carp is prepared to stuff it' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he's caught the carp is prepared' is the wordplay.
'he' becomes 'to' (I can't explain this - if you can you should give a lot more credence to this answer).
'caught' is an insertion indicator.
'is prepared' indicates an anagram.
'carp' anagrammed gives 'capr'.
'to' inserted within 'capr' is 'CAPTOR'.
Can you help me to learn more?
(Other definitions for captor that I've seen before include "One taking a prisoner" , "Holder of a prisoner" , "To carp (anag)" , "The one who holds the prisoner" , "kidnapper, perhaps" .)