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David Attenborough dives with grey reef sharks on a coral reef, and talks about their streamlining. This was one of the first instances of underwater presenting, made possible by the full face plate that allowed David Attenborough to talk and still breathe. The sharks and shoals of smaller fish swim around David. He outlines the difference between cartilaginous fish like sharks and the more common, bony fishes. Bony fish have swim bladders and much more manouevrable fins than cartilaginous fish do. A montage of different types of bony fish in shoals.