Perhaps Sturgeon's entertaining in conclusion (6)
I believe the answer is:
finish
'conclusion' is the definition.
(I know that conclusion can be written as finish)
'perhaps sturgeon's entertaining in' is the wordplay.
'perhaps sturgeon' becomes 'fish' (sturgeon is a type of fish).
'entertaining' is an insertion indicator.
'fish' placed around 'in' is 'FINISH'.
(Other definitions for finish that I've seen before include "End or terminus" , "Patina" , "Deal with" , "End, complete" , "Conclude, stop" .)