There's something about fish that leaves a cold, slimy whiff in many people's minds. Either that, or fish are simply "food"; catching fish to eat is so deeply ingrained that we fish for fish, but we don't pigeon a pigeon or deer a deer. It's difficult to think of fish as wild, living things, partly because those chunks of white meat on our plates are almost impossible to connect to animate, living, breathing creatures.

Wild fish hover in seas, rivers and lakes, out of sight and out of mind. But from the very first time Helen Scales immersed herself into their liquid world, she realized that fish are beautiful, mesmerizing, complex and exciting. The moment she sank down to eyeball a wild trout-the fish poised in front of her, expertly occupying the three-dimensional space in a way that she could only dream of imitating-sparked the ichthyologist within, and set in motion years of study and exploration in the fishes' unseen domain as she became a devoted fish-watcher.

In this book, Scales shares the secrets of fish, unhitching them from their reputation as cold, unknowable beasts and reinventing them as clever, emotional, singing, thoughtful creatures, and challenging readers to rethink these animals. She takes readers on an underwater journey to watch these creatures going about the hidden but glorious business of being a fish. Their way of life is radically different from our own, in part because they inhabit a buoyant, sticky fluid in which light, heat, gases and sound behave in odd ways. They've evolved many tactics to overcome these challenges, to become megastars of the life sun-aquatic. In doing so, these extraordinary animals tell us so much about the oceans and life itself. Our relationship with these scaly creatures goes much deeper than predator versus prey. Fish leave their mark on the human world.

As well as being a rich and entertaining read, this book will inspire readers to think again about these animals, and the seas, and to go out and appreciate the wildness and 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.

Helen Scales is a marine biologist, diver, surfer, broadcaster and writer who's spent hundreds of hours underwater watching fish. A familiar voice for the oceans, she's pondered the mysteries of the deep sea with Robin Ince and Brian Cox on BBC Radio 4's The Infinite Monkey Cage and donated an imaginary tank of seahorses to The Museum of Curiosity. She's a regular writer for BBC Focus and BBC Wildlife magazines. Among her radio documentaries she's explored the dream of living underwater and followed the trail of endangered snails around the world and back again.

Helen's recent book, Spirals in Time, is a Guardian bestseller. It was shortlisted for the Royal Society of Biology book prize, picked as a book of the year by The Economist, Nature, The Times and the Guardian and was BBC Radio 4's Book of the Week.