Demo fish are commonly used in aquariums to showcase different species. These fish are often colorful and easy to care for, making them popular among hobbyists. When introducing demo fish to a new tank, it is important to acclimate them slowly to prevent stress. Providing a suitable environment with proper water conditions is essential for the well-being of demo fish. Some common types of demo fish include guppies, tetras, and mollies. Overall, demo fish serve as great educational tools for learning about aquatic life.