Marine fish, a food not fully digested in Hebridean isle (9)
I believe the answer is:
barracuda
'marine fish' is the definition.
'barracuda' can be an answer for 'fish' (barracuda is a kind of fish). I am not sure about the 'marine' bit.
'a food not fully digested in hebridean isle' is the wordplay.
I cannot really see how this works, but
'a' is within the answer.
'food' could be 'cud' (cud is a kind of food) and 'cud' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for barracuda that I've seen before include "Voracious marine fish" , "Voracious tropical fish" , "Large predatory sea fish" , "Vicious swimmer" , "Marine attacker" .)