Explaining Nature on Instagram: "Fish are aquatic animals that live in both fresh and salt water and breathe through gills instead of lungs. They are cold-blooded, meaning their body temperature changes with the water around them. Most fish have scales covering their bodies, fins for swimming, and a streamlined shape that helps them move efficiently through water. There are three main groups of fish: bony fish (like salmon and tuna), cartilaginous fish (like sharks and rays), and jawless fish (l