Wager fish will be gravely disloyal (6)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
betray
'be gravely disloyal' is the definition.
I can't judge whether this defines the answer.
'wager fish' is the wordplay.
'wager' becomes 'bet' (synonyms).
'fish' becomes 'ray' (ray is a kind of fish).
'bet'+'ray'='BETRAY'
'will' is the link.
Can you help me to learn more?
(Other definitions for betray that I've seen before include "26 [SELL]" , "Act treacherously towards (someone)" , "Double-cross like Judas" , "grass" , "Be a traitor" .)