Extra bit of fish was unwrapped (4)
I believe the answer is:
coda
'extra bit' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'fish was unwrapped' is the wordplay.
'fish' becomes 'cod' (type of fish).
'unwrapped' means to look at the middle letters (the letters which wrap the word are removed).
The middle letter of 'was' is 'a'.
'cod'+'a'='CODA'
'of' is the link.
Can you help me to learn more?
(Other definitions for coda that I've seen before include "Conclusion of work" , "End of movement" , "Final part of mus. structure" , "Final section" , "Closing passage of musical piece" .)