1. Respiration: Dolphins are air-breathing mammals, which means they must periodically come to the surface to breathe air through their blowholes. Fish, on the other hand, are aquatic vertebrates with gills that extract oxygen from water.
2. Body Temperature: Dolphins are warm-blooded mammals, meaning they can regulate their body temperature internally. Fish, on the other hand, are cold-blooded, meaning their body temperature varies with their surroundings.
3. Reproduction: Dolphins give birth to live young and care for them after they're born. They nurse their offspring with milk produced by mammary glands. Fish, on the other hand, lay eggs that hatch into free-swimming larvae that must fend for themselves.
4. Skeletal Structure: Dolphins have a backbone and a bony skeleton, which is a characteristic feature of mammals. Fish, on the other hand, have a cartilaginous skeleton, which is made of cartilage rather than bone.
5. Skin: Dolphins have smooth skin, whereas fish have scales. Dolphin skin is also much thicker and more flexible than fish scales, allowing them to swim more efficiently through the water.
6. Intelligence: Dolphins are known for their exceptional intelligence and complex social structures, which are not typically seen in fish. They display self-awareness, problem-solving abilities, and the capacity for social learning and cooperation.
In summary, dolphins are mammals, not fish, due to their air-breathing, warm-bloodedness, live births, mammary glands, bony skeletons, smooth skin, and high levels of intelligence.