Initial slice of tuna fish in mess (6)
I believe the answer is:
tangle
'mess' is the definition.
(I've seen this before)
'initial slice of tuna fish' is the wordplay.
I cannot really understand how this works, but
'fish' could be 'angle' (angle can mean to fish) and 'angle' is found within the answer.
A single letter 't' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'in' is the link.
Can you help me to learn more?
(Other definitions for tangle that I've seen before include "'Twisted mess, muddle (6)'" , "Enmesh, snarl up" , "Confused state; seaweed" , "Knotted, twisted mass" , "A fight; seaweed" .)