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 determine which of the following is a feature of bony fish, we need to analyze each option provided in the question.

1. **Placoid scales present**: Placoid scales are characteristic of cartilaginous fish (like sharks and rays), not bony fish. Bony fish typically have cycloid or ctenoid scales. Therefore, this option is incorrect.

2. **Gills without operculum**: Bony fish have gills covered by a bony plate called the operculum. This structure aids in respiration by helping to pump water over the gills. Therefore, this option is also incorrect.

3. **Habitat of marine water only**: Bony fish can inhabit both freshwater and marine environments. Therefore, stating that they are only found in marine water is incorrect.

4. **Air bladder absent**: Most bony fish possess an air bladder (also known as a swim bladder), which helps them maintain buoyancy. Therefore, this option is incorrect as well.

After analyzing all the options, we find that the only correct feature of bony fish is that they have gills with an operculum.

**Final Answer**: The correct feature of a bony fish is **Gills with operculum**.