Cartilaginous fishes swim continuously without any interval. Give reason.

Explanation

**Step-by-Step Solution:**

1. **Understanding Cartilaginous Fishes**: Cartilaginous fishes, such as sharks and rays, belong to a group of fishes characterized by having a skeleton made of cartilage rather than bone.

2. **Absence of Swim Bladder**: One of the key features of cartilaginous fishes is that they do not possess a swim bladder. A swim bladder is an internal gas-filled organ that helps bony fishes maintain buoyancy in the water.

3. **Buoyancy and Its Importance**: The swim bladder allows bony fishes to control their buoyancy, enabling them to float at different depths without expending energy. In contrast, cartilaginous fishes lack this adaptation.

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