Fish in turn goes bad (8)
I believe the answer is:
sturgeon
'fish' is the definition.
(sturgeon is a kind of fish)
'turn goes bad' is the wordplay.
'bad' indicates anagramming the letters.
'turn'+'goes'='turngoes'
'turngoes' anagrammed gives 'STURGEON'.
'in' is the link.
(Other definitions for sturgeon that I've seen before include "Shark-like fish" , "So urgent to find caviar-bearing fish" , "Fish yielding caviar and isinglass" , "caviar suppliers" , "Fish valued for caviar" .)