Snakelike swimmers (4)
I believe the answer is:
eels
'snakelike swimmers' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for eels that I've seen before include "Elongated fish" , "Fish (that may be jellied)" , "Abstract nineteen sixties style" , "Elongated fishes" , "Snakes wriggling in lees" .)