Which of the following is a feature of a bony fish?

Options

A. Placoid scales present
B. Gills with operculum
C. Habitant of marine water only
D. Air bladder absent

Answer

To solve the question "Which of the following is a feature of a bony fish?", we will analyze the characteristics of bony fish and compare them with the options provided.

### Step-by-Step Solution:

1. **Identify Bony Fish**:
- Bony fish, such as Rohu and Katla, are characterized by their bony skeletons as opposed to cartilaginous fish (like sharks) which have cartilage-based skeletons.

2. **Evaluate the Options**:
- **Option 1: Placoid Scales Present**:
- Placoid scales are found in cartilaginous fish, not in bony fish. Bony fish have different types of scales, such as ctenoid or cycloid scales. Therefore, this option is incorrect.

- **Option 2: Gills with Operculum**:
- Bony fish possess gills covered by a bony flap called the operculum. This structure aids in respiration by helping to pump water over the gills. This is a defining feature of bony fish. Therefore, this option is correct.

- **Option 3: Habitat of Marine Water**:
- While some bony fish live in marine environments, others, like Rohu and Katla, are found in freshwater. Thus, this option is misleading and incorrect as it does not apply to all bony fish.

- **Option 4: Air Bladder Absence**:
- Bony fish typically have an air bladder (swim bladder) that helps them maintain buoyancy in the water. Therefore, stating that bony fish lack an air bladder is incorrect.

3. **Conclusion**:
- The only correct feature of bony fish from the options provided is **gills with operculum**.

### Final Answer:
The feature of a bony fish is **gills with operculum**.