I'm pleasantly surprised after cold salmon (4)
I believe the answer is:
coho
'salmon' is the definition.
(type of salmon)
'i'm pleasantly surprised after cold' is the wordplay.
'i'm pleasantly surprised' becomes 'oho' (I can't explain this - if you can you should give a lot more credence to this answer).
'after' says to put letters next to each other.
'cold' becomes 'C' (eg on taps).
'oho' put after 'c' is 'COHO'.
Can you help me to learn more?
(Other definitions for coho that I've seen before include "Fish" , "Small north Pacific salmon" .)