Seventy per cent of the earth's surface is covered by water. This vast aquatic realm is inhabited by a multitude of strange creatures and reigning supreme among them are the fish. There are giants that live for centuries and thumb-sized tiddlers that survive only weeks; they can be pancake-flat or inflatable balloons; they can shout with colours or hide in plain sight, cheat and dance, remember and say sorry; some rarely budge while others travel the globe restlessly. And yet the mesmerising and complex lives of fish remain largely underrated and unseen, living hidden beneath the waterline, out of sight and out of mind. Helen Scales is our guide on an underwater journey, as we fathom the depths and watch these animals going about the glorious business of being fish. As well as the fish, we meet devoted fishwatchers past and present, from voodoo zombie potion hunters and scientists who taught fish how to walk to nonagenarian explorers of the deep sea. Woven throughout are vignettes of Helen's own aquatic explorations, from eerie nighttime dives with glowing fish and up-close encounters with giant manta rays, to floating in the middle of a swirling shoal being watched by thousands of inquisitive eyes. As well as being a rich and entertaining read, this book will inspire readers to think again about these animals and the seas they inhabit, and to go out and appreciate the wonders of fish, whether through the glass walls of an aquarium or, better still, by gazing into the fishes' wild world and swimming through it.