Clue: Bivalves discovered near quarry? It's a bit fishy (7)
Answer: LAMPREY
Explanation: Definition: It's a bit fishy

(c)**LAM**(s) ("bivalves", *discovered*) *near* **PREY** ("quarry")
 

 
*A lamprey is a jawless fish, so "it's a bit fishy" is a bit loose as far as definitions go, in my opinion,