From the Okavango swamps in Africa there are stories of a piranha-like fish that hunts in marauding packs, tearing into other fish, and even human flesh. Jeremy Wade heads into the watery labyrinth to track down this deadly swarm.From the Okavango swamps in Africa there are stories of a piranha-like fish that hunts in marauding packs, tearing into other fish, and even human flesh. Jeremy Wade heads into the watery labyrinth to track down this deadly swarm.