Little light fish (3)
I believe the answer is:
ray
'fish' is the definition.
(I know that ray is a type of elasmobranch)
'little light' is the wordplay.
'little' means to remove the last letter (the word is not quite complete).
'light' becomes 'rays'.
'rays' with its last letter removed is 'RAY'.
(Other definitions for ray that I've seen before include "may be electric" , "A bright beam or flat fish" , "Broad flat fish; beam" , "A little light" , "Beam - skate" .)