What are three key characteristics of fish?

1. Aquatic vertebrates: Fish are animals belonging to the phylum Chordata, which means they have a backbone, and they live exclusively in water.

2. Gills for respiration: Fish use gills to extract oxygen from the water and release carbon dioxide. This is crucial for their survival in aquatic environments.

3. Fins for locomotion: Fish use fins for movement, steering, and balance in the water. These fins come in various shapes and sizes, depending on the species and its lifestyle.