Fish food: idiot has loads (8)
I believe the answer is:
grayling
'fish' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for grayling that I've seen before include "Fish of the salmon family" , "Butterfly" , "Salmonoid fish" , "Catch" , "Fish - philosopher" .)