A jawless fish lays eggs in fresh water and its ammocoetes larvae after metamorphosis. This fish returns to the ocean as _.

Explanation

The jawless fish that lays eggs in fresh water and its ammocoetes larvae after metamorphosis and returns to the ocean is Petromyzon. It is also known as the sea lamprey. Petromyzon is a member of the class Cyclostomata, which includes all jawless fish. The life cycle of Petromyzon begins with the adults spawning in freshwater. The eggs hatch into ammocoetes larvae, which live in freshwater for several years. After metamorphosis, the young lampreys migrate to the ocean, where they live for the rest of their lives.