Fish are the most varied and diverse backboned creatures on the planet. They range from pregnant males to fish that fly, to those that have a top speed faster than a cheetah -- sailfish.
In this episode, the brightly colored weedy sea dragon's unusual mating and parenting methods are revealed, as is the peculiar convict fish, which shares its network of tunnels with thousands of offspring, who do the reclusive parents' bidding.
In Hawaii, gobies climb waterfalls -- some more than 400 feet high -- using a specialized disc that enables them to stick to vertical rocks. The sarcastic fringehead fiercely defends its territory from octopi and rival fringefish. And Japanese mudskippers spend many of their waking hours out of water -- feeding, leaping and fighting for the attentions of the opposite sex.