Fish from which caviar is obtained (8)
I believe the answer is:
sturgeon
'fish from which caviar is obtained' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for sturgeon that I've seen before include "Fish sought for caviar" , "swimmer" , "Caviare-yielding fish" , "caviar suppliers" , "Fish producing caviare" .)