Long, skinny fish (3)
I believe the answer is:
eel
'long skinny fish' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for eel that I've seen before include "Apode" , "User of electric organ" , "Elongated fish" , "Wriggly fish" , "Serpentine fish" .)