The Fascinating World of Fish

Fishes were the first vertebrates, appearing 500 million years ago. Today, over 25,000 species exist. Fishes breathe using gills, which extract oxygen from water. They are ectotherms, meaning their body temperature varies with the environment. Fishes use fins for movement and have keen senses. Most hatch from eggs. There are various types, including sharks with cartilage skeletons and others with bony skeletons.

What are the first vertebrates on Earth according to fossil evidence?

How do fishes breathe?

What is the significance of gills in fishes?

What are ectotherms and how do they relate to fishes?

What structures help fishes to swim?