Deep voice; freshwater fish (4)
I believe the answer is:
bass
I believe this clue is a double definition.
'deep voice' is the first definition.
(I've seen this before)
'freshwater fish' is the second definition.
(bass is a kind of freshwater fish)
(Other definitions for bass that I've seen before include "Variety of sea and freshwater perch" , "Very low - perch" , "Male singer and saltwater fish" , "Fish - low in pitch" , "Low fellow" .)