Name the branch of biology deals with rearing, catching, selling of fish, molluscs and crustacean.

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the branch of biology that involves the rearing, catching, and selling of aquatic organisms such as fish, molluscs, and crustaceans.

2. **Defining Key Terms**:
- **Rearing**: This refers to the nurturing or raising of aquatic animals until they reach a certain size or maturity.
- **Catching**: This involves the act of capturing these aquatic organisms from their natural habitats.
- **Selling**: This is the commercial aspect where these organisms are sold for consumption or other purposes.

3. **Identifying the Organisms**: The question specifically mentions:
- **Fish**: Aquatic animals that are typically gilled and live in water.
- **Molluscs**: A diverse group that includes animals like octopus and snails.
- **Crustaceans**: This group includes animals such as prawns and crabs.

4. **Branch of Biology**: The branch of biology that encompasses the practices of rearing, catching, and selling these aquatic organisms is known as **Aquaculture**.

5. **Conclusion**: Therefore, the answer to the question is **Aquaculture**.

---