Gill cover is absent in :

Options

A. Shark
B. Labeo
C. Salmon
D. All of these

Answer

To determine in which fish the gill cover is absent, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Classes of Fish**:
- Fish are primarily classified into two main classes:
- **Chondrichthyes**: These fish have an endoskeleton made of cartilage.
- **Osteichthyes**: These fish have an endoskeleton made of bone.

2. **Identify the Gill Cover (Operculum)**:
- The gill cover, also known as the operculum, is a bony structure that covers the gills in fish.
- It is present in fish belonging to the class Osteichthyes.

3. **Analyze the Options**:
- **Option A: Shark** - Sharks belong to the class Chondrichthyes, which means they do not have a gill cover.
- **Option B: Labio** - Labio (often referred to as "Labeo") belongs to the class Osteichthyes, so it has a gill cover.
- **Option C: Salmon** - Salmon also belongs to the class Osteichthyes, meaning it has a gill cover.
- **Option D: All of these** - This option implies that all listed fish lack a gill cover, which is incorrect.

4. **Conclusion**:
- Since only sharks (class Chondrichthyes) lack a gill cover, the correct answer is **A: Shark**.

### Final Answer:
The gill cover is absent in **A: Shark**.

---