Fish; singer (4)
I believe the answer is:
bass
I believe this clue is a double definition.
'fish' is the first definition.
(bass is a kind of fish)
'singer' is the second definition.
(I know that bass is a type of singer)
(Other definitions for bass that I've seen before include "bottom of sound?" , "Fish, guitar" , "Low singing voice" , "Freshwater fish and lowest voice" , "Lowest register of the male voice" .)