Gutted kipper and green whale food (5)
I believe the answer is:
krill
'whale food' is the definition.
(I've seen this in another clue)
'gutted kipper and green' is the wordplay.
'gutted' means to remove the middle letters (to gut something is to remove its insides).
'and' is a charade indicator (letters next to each other).
'green' becomes 'ill' (I can't explain this - if you can you should give a lot more credence to this answer).
'kipper' with its centre taken out is 'kr'.
'kr'+'ill'='KRILL'
Can you help me to learn more?
(Other definitions for krill that I've seen before include "Whale food" , "Whales' staple diet" , "seafood" , "Food of whalebone whales" , "Small aquatic creatures" .)