Eye of the Shoal by Helen Scales

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Reviewed by Annabel

Eye of the Shoal by Helen Scales

In her third book, Helen Scales tuns her attention to another branch of the marine tree of life with each book. She began with the small genus of seahorses; her second book, Spirals in Time (reviewed here), described the large and varied world of molluscs – the second largest phylum of invertebrates. For her third book she moves across into the world of backboned sea creatures – fish.

After an introduction in which Scales (what a good name for an ichthyologist!) gives us a brief tour of her experiences with fish, the first chapter proper delves into the history of ichthyology through the ages, complete with some lovely illustrations of sea monsters.

The first problem we have though is to define the term ‘fish’, because fish are not a monophyletic group, the fish family tree has a second branch to it:

Strictly speaking, if we insist on sticking to the rules of taxonomy, humans are fish together with all the other land-dwelling tetrapods.

Yes, we all came from the sea! However, this book is only concerned with the fish that, ‘stayed behind and carried on evolving and doing their own things underwater.’

The next chapter looks at the fish family tree and its twelve groupings in more detail, from the largest group, the Teleosts, which count goldfish and tuna in their numbers,down to the most ancient slime-producing hagfish, via sturgeon, gars, coelocanths, sharks and rays.

As she surveys each group, Scales brings out some essential facts. I knew sturgeons were big, but a female Beluga Sturgeon, can be longer and bigger than a Beluga Whale at eight metres. She produces the most prized caviar from her ovaries which can comprise a quarter of her body weight. It’s no surprise that most sturgeon species are threatened with extinction on the Red List and, she tells us in a shocking footnote:

Most caviar-hunters don’t wait for the females to lay their eggs, but cut them out.

We move on now, to look at how and where fish live and their many and varied adaptations, starting with colour. Many fish have developed eye-spots on their bodies, perhaps to divert attention from their heads; others are patterned and striped in ways that break up their outline and allow them to hide in plain sight like the blue and yellow Emperor Angelfish. Others can change their colour to coordinate with their background like the Slender Filefish in the Caribbean, a quick-change artist which matches whatever it is swimming past. Next, she explores the world of bioluminescence and it is surprising to find out how many fish glow in the dark, or light up like the Angler fish from the deepest deeps.

The chapter on the anatomy of a shoal will bring to mind the amazing films in the TV series Blue Planet where sardines shoal, creating safety in numbers, even if predators lurk on the edges. Scales discusses how a shoal is like a cycling peloton, the slipstream helping the fish behind to use less energy, and how a fish’s shape determines how it swims.

A particularly fascinating chapter is the one on toxic fish. There are around 3000 poisonous fish known, of which the most notorious is the pufferfish, which people still risk their lives to eat as fugu. Reading on, Scales enlightens us about the poison known as TTX, which is produced by bacteria:

A single milligram of this potent neurotoxin – a droplet small enough to sit on the head of a pin – will kill a fully grown human. Cooking doesn’t deactivate it. There’s no known antidote. (…)

Give them bacteria-free food and puffers gradually lose their potency. In this way, fish-famers have produced puffers that are guaranteed safe to eat, but they’ve proving unpopular among Japanese diners who still value the thrill of eating wild-caught fugu.

Subsequent chapters look at the fish in the fossil record and how fish make sounds, before coming to the final chapter which looks at the question of sentience and consciousness. The author tells us that:

Studies are chipping away at this assumption that we can get away with treating fish as lesser beings. (…) It’s becoming clear that fish live complex, intelligent and nuanced lives, and evidence is stacking up that fish can suffer, that they get scared and they can feel pain.

In her book about molluscs, Scales included a lot of cultural and mythological references to these creatures in the main text. In Eye of the Shoal, she takes a different approach, keeping the body of the book scientific and observational, but there is still a place for some fishy tales from around the world. At the end of each chapter there is a short story – from the Irish tale of the ‘Salmon of Knowledge’ and the Persian ‘Doctor of the Sea’ to the Icelandic ‘Vatnagedda’ which if you can catch one will protect against evil spirits. Fish have a definite place in folklore.

As in Spirals in Time, Scales’ enthusiasm for her subject shines through. Explanations are clear and succinct, there is much humour and empathy too. There is, alas, no section of colour plates in this volume, just a few mostly historic or taxonomic illustrations and diagrams, plus the lovely fishy pen drawings prefacing each chapter and the folktales. However, this underwater world comes alive in the quality of Scales’ writing in this fascinating volume which was a pleasure to read.

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Annabel is one of the Shiny Editors.

Helen Scales, Eye of the Shoal (Bloomsbury Sigma, 2018) ISBN 9781472936844, hardback, 320 pages.

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