Fish not a sausage male's thrown back (6)
I believe the answer is:
marlin
'fish' is the definition.
(I've seen this before)
'not a sausage male's thrown back' is the wordplay.
'not a sausage' becomes 'nil' (both can mean zero or nothing).
'male' becomes 'ram' (male sheep).
'thrown back' says the letters should be written backwards.
'nil'+'ram'='nilram'
'nilram' in reverse letter order is 'MARLIN'.
(Other definitions for marlin that I've seen before include "Spearfish" , "Large oceanic sport fish" , "Large game fish" , "Large ocean fish" , "Large sea-fish" .)