Flatfishes (4)
'flatfishes' is the definition.
(I know this)
This is all the clue.
(Other definitions for dabs that I've seen before include "Fingerprints (colloq.)" , "Fingerprints (slang)" , "they give evidence to police" , "Fish < experts" , "'Pats at, with a cloth, say (4)'" .)
(Other definitions for rays that I've seen before include "Columns of light or heat" , "Sunbeams" , "They swim" , "shafts" , "Beams - fish" .)