Operator will guzzle starter of these fish (8)
I believe the answer is:
sturgeon
'fish' is the definition.
(sturgeon is a kind of fish)
'operator will guzzle starter of these' is the wordplay.
'operator' becomes 'surgeon' (I've seen this before).
'will guzzle' is an insertion indicator.
'starter of' says to take the initial letters.
The initial letter of 'these' is 't'.
'surgeon' enclosing 't' is 'STURGEON'.
(Other definitions for sturgeon that I've seen before include "Fish yielding caviar and isinglass" , "caviar suppliers" , "Egg producer" , "producer of caviar" , "Our gents caught a large fish" .)