Seal savaged fish keeping its head down - ray? (5,4)
I believe the answer is:
laser beam
'ray?' is the definition.
(laser beam is a kind of ray)
'seal savaged fish keeping its head down' is the wordplay.
I cannot really understand how this works, but
an anagram of 'seal' is 'lase' which is present in the answer.
This explanation may well be incorrect...
(Other definitions for laser beam that I've seen before include "Shaft of light or electro-mechanic radiation" , "Intense ray of light" , "Column of intensified light" , "penetrating light" , "Shaft of light or electromagnetic radiation" .)