It has become cliché to say that we know more about the surface of Mars than we do about the depths of our oceans, inaccessible as they are to us landlubbers. Nevertheless, technological advances have allowed us to discover more and more about the denizens of the deep. Anyone who has watched Blue Planet II or similar recent documentaries can testify to the bizarre and wonderful life forms that can be found there.

Priede’s work provides an academic treatise on the biology, ecology and diversity of deep-sea fishes. About half of the book is dedicated to a systematic summary of all the families to be found. As quickly becomes clear, the deep sea provides a home for fish right across the taxonomic spectrum, with the vast majority of families having at least some species living here. The book is not intended to allow species identification. Especially the FAO has published books and guides to that end, as this much information could never be contained in a few hundred pages. Instead, this book should allow you to look up fish caught at sea and retrieve information to genus level, with notable and important species described in some detail. Line drawings are provided of representative members of important families, revealing some of the weird and wonderful fish to be found. Clearly, there is much more to the deep-sea fish fauna than the famous anglerfishes, whose bizarre appearance have attracted so much attention that they have been the subject of a separate book (Oceanic Anglerfishes: Extraordinary Diversity in the Deep Sea). Although a plate section is included, this is no pictorial work. If you want to gawk at photos of bizarre-looking fish, you’re better off reading Creatures of the Deep: In Search of the Sea’s Monsters and the World They Live in or Life in the Dark: Illuminating Biodiversity in the Shadowy Haunts of Planet Earth. This part of Deep-Sea Fishes is really a reference work, not necessarily intended to be read, more to be consulted.

This core is bookmarked by chapters on the deep sea, its colonisation by fishes in evolutionary history, their adaptations to living here, a description of the faunas by area and depth zone, and, as seems unavoidable nowadays, a section about the impact of fisheries. This makes for informative reading and taught me a lot I didn’t know yet.

“[…] the deep sea is not just a featureless bathtub […] the land is topographically as varied as that above sea level”

Most of us will have at least a dim awareness that the deep sea is not just a featureless bathtub. Anyone familiar with plate tectonics will have heard of the Ring of Fire or the mid-Atlantic Ridge. But the deep sea has many underwater features, and the land here is topographically as varied as that above sea level. Special mention is made of hydrothermal vents and cold seeps, which provide oases of heat and chemicals in the deep and were only confirmed to exist in 1977 (see The Ecology of Deep-Sea Hydrothermal Vents). What is astonishing are the maps showing just how much of the planet is deep sea. The evocatively named abyssal (3000-6000 m) and hadal (>6000 m) zones make up more than 53% of the planet’s surface area. Fish do not occur uniformly throughout this enormous body of water though, with most of them hugging the contours of the bottom, creating vast swathes of water that sit over deep bottoms that are relatively devoid of permanent fish life, though there is plankton, vertically migrating fish, and eggs and juveniles galore in many areas. As the section on adaptations makes clear, there’s a physiological depth limit to fish life (about 8400 m) below which they cannot survive. Around the deepest trenches, such as the Mariana trench, this has interesting results, with the walls of trenches hosting fish fauna, but not all fish able to traverse the open deep-water chasms to the other side.

The chapter on adaptations to life in the deep sea is similarly fascinating in revealing the many outlandish solutions that have evolved to meet the unique challenges of this environment. The chapter is thorough, obviously covering well-known traits such as the extreme eyes or bioluminescent lures, but also providing in-depth accounts of physiological adaptations such as buoyancy mechanisms, and circulation and respiration.

“[…] areas that are repeatedly targeted for bottom trawling are akin to agricultural pastures on land […]”

The chapter on fisheries outlines the same story as All the Boats on the Ocean, describing the rise of intensive factory fishing by the USSR and other nations, and the collapse of fish stocks worldwide, with the industry exploiting and exhausting species after species. But there are many interesting details here, such as the different effects of the different types of fishing methods. One author has suggested that areas that are repeatedly targeted for bottom trawling are akin to agricultural pastures on land from the point of view of environments modified by humans. For the deep-sea fish fauna, the one saving grace is that physiological adaptations mean that many species are small, have a very low metabolism, low muscle mass and high water content in their body, making them commercially unattractive. This doesn’t stop destruction caused by by-catch, especially as rapidly being hauled to the surface from these depths is lethal in itself for many fishes.

Cambridge University Press has published a number of fascinating scholarly works on the deep sea in recent years (see The Hadal Zone: Life in the Deepest Oceans and Discovering the Deep: A Photographic Atlas of the Seafloor and Ocean Crust) and this book joins that line-up. The book has a pleasant weight and the binding and paper used make for a book that will lay open on a surface for reference and study. The production is slightly marred by some typos and figure references in the text not pointing to the correct figure panels, but these are infrequent enough not to be a big distraction. Deep-Sea Fishes might be too academic for a general audience, but if you really want to know the nuts and bolts of the topic, or you study this topic professionally in whatever guise, this book is an unparalleled source of information that you cannot do without. Even though new information becomes available continuously (for example, as I was writing this review, a study was published in Scientific Reports showing that hydrothermal vents could function as egg-incubators for a deep-sea skate), Deep-Sea Fishes is a synthesis that will be the go-to reference for years to come.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

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