Jiggle small fish (5)
I believe the answer is:
shake
'jiggle' is the definition.
(I know that jiggle is a more specific form of the action shake)
'small fish' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'fish' becomes 'hake' (type of fish).
's'+'hake'='SHAKE'
(Other definitions for shake that I've seen before include "Vibrate; drink" , "Rattle" , "Upset" , "Tremble, quake" , "Judder" .)