It's expressed vocally as they prod gutted salmon outside (6)
I believe the answer is:
spoken
'it's expressed' is the definition.
(similar in meaning)
'prod gutted salmon outside' is the wordplay.
'prod' becomes 'poke' (synonyms).
'gutted' suggests removing the centre (to gut something is to remove its insides).
'outside' means one lot of letters goes inside another (some letters go outside others).
'salmon' with its centre removed is 'sn'.
'poke' put into 'sn' is 'SPOKEN'.
'vocally as they' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for spoken that I've seen before include "Verbalised" , "Oral" , "Said" , "Declared" , "Uttered through the medium of speech" .)