Dolphins are mammals and not fish. They feed their babies on milk like we do.
Dolphins have lungs and breathe air like we do but they can hold their breath for more than 10 minutes!
Dolphins sleep while they are swimming. During their nap, half of the brain is asleep and only one eye is closed.
Can you imagine that dolphins recognize themselves in a mirror? They have self-awareness like we do and are very intelligent.
They can also hunt in the dark without seeing with their eyes, making click sounds using so called echolocation (Biosonar) allows them to find food without using their sense of sight.