Controlled ray and bream sale at sea (5,4)
I believe the answer is:
laser beam
'controlled ray' is the definition.
(electronic ray of light)
'bream sale at sea' is the wordplay.
'at sea' is an anagram indicator.
'bream'+'sale'='breamsale'
'breamsale' with letters rearranged gives 'LASER BEAM'.
'and' acts as a link.
(Other definitions for laser beam that I've seen before include "Intense ray of light" , "Shaft of light or electromagnetic radiation" , "penetrating light" , "Shaft of light or electro-mechanic radiation" , "Column of intensified light" .)