Bottlenose dolphins and some other cetaceans also have a dorsal fin on their backs to help with balance. There are no bones inside the dorsal fin, rather it is made of fibrous connective tissue. The tail fins, or flukes, are also made totally of fibrous connective tissue. Dolphins are excellent divers. They can hold their breath for up to ten minutes when diving.
Dolphins have good eyesight and excellent hearing.
Dolphin send out a series of clicking sounds which travel forward. These sounds bounce off objects and return to the middle ear through the jawbone. These echoes tell a dolphin very precise information about objects such as their distance, shape, density, texture, and size. A dolphin can easily tell two kinds of fish apart with its echolocation, even when the water is dark and murky.