In which the following fish the skin is tough containing minute placoid scales?

Options

A. Exocoetus
B. Hippocampus
C. Scoliodon
D. Labeo

Answer

To determine which fish has tough skin containing minute placoid scales, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Placoid Scales**:
- Placoid scales are tough, microscopic structures that are covered with hard enamel. They are unique to certain types of fish.

2. **Identify the Type of Fish**:
- Placoid scales are found only in cartilaginous fishes, which are also known as elasmobranchs. This group includes sharks and rays.

3. **Evaluate the Options**:
- **Exocoitus**: This is a genus of flying fishes, which belong to the class of bony fishes. Bony fishes have cycloid scales, not placoid scales. Therefore, this option is incorrect.
- **Hippocampus**: Commonly known as seahorses, these also belong to the class of bony fishes and do not have placoid scales. This option is also incorrect.
- **Scoliodon**: This refers to a type of shark, which is a cartilaginous fish. Scoliodon has tough skin with placoid scales. Thus, this option is correct.
- **Labio**: Known as Rohu, this is a freshwater bony fish found in India. Like the others, it does not have placoid scales. This option is incorrect.

4. **Conclusion**:
- After evaluating all the options, the fish that has tough skin containing minute placoid scales is **Scoliodon**.

### Final Answer:
The fish with tough skin containing minute placoid scales is **Scoliodon**.

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