Remove head from rotter's fish (4)
I believe the answer is:
eels
'fish' is the definition.
(eel is a type of fish)
'remove head from rotter's' is the wordplay.
I cannot quite see how this works, but
'from' could be 'e' (I've seen this in other clues) and 'e' is found in the answer.
The remaining letters 'els' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for eels that I've seen before include "(Slippery) fish" , "Congers" , "Elongated fishes" , "Slippery creatures" , "Elongated fish" .)