A jawless fish which lays eggs in fresh water and whose ammocoete larve after metamorphosis return to ocean is

Options

A. Eptatretus
B. Myxine
C. Neomyxine
D. Petromyzon

Explanation

To solve the question about a jawless fish that lays eggs in freshwater and whose ammocoete larvae return to the ocean after metamorphosis, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Class of Fish**: The question specifies a "jawless fish," which indicates that we are looking for a fish from the class Cyclostomata. This class is characterized by the absence of jaws.

2. **Consider the Reproductive Habits**: The fish in question lays eggs in freshwater. This detail is crucial for narrowing down our options within the Cyclostomata class.

3. **Identify the Fish**: The specific fish that fits this description is the Petromyzon, commonly known as the lamprey. Lampreys are jawless fish that migrate from the ocean to freshwater to spawn.

4. **Understand the Life Cycle**: After laying eggs in freshwater, the eggs hatch into larvae known as ammocoetes. These larvae live in freshwater for several years before undergoing metamorphosis.

5. **Metamorphosis and Migration**: After metamorphosis, the adult lampreys migrate back to the ocean, completing their life cycle.

6. **Conclusion**: Therefore, the answer to the question is the Petromyzon, or lamprey.

### Final Answer:
The jawless fish that lays eggs in freshwater and whose ammocoete larvae return to the ocean after metamorphosis is the **Petromyzon** (lamprey).

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