S1, E4: A look at how fish dominate the planet's waters through their variety of shape and behaviour. The male weedy sea dragon protects its eggs by carrying them on his tail, while the sarcastic fringehead appears to turn its head inside out when it fights. Later, slow motion cameras show flying fish gliding through the air like a flock of birds, and capture the world's fastest swimmer, the sailfish, plucking sardines from a shoal.