This book is truly comprehensive. It begins with an overview of relevant features of the hosts and this sets the scene for later consideration of site specificity, effects of infection on various host tissues, and the capacity for resistance and repair. There is a chapter on protozoan parasites and then 4 chapters (90 pages) on monogeneans, the group on which Kearn has made such a distinctive research contribution. A major section is devoted to crustacean parasites – 8 chapters (over 140 pages), including 5 chapters on copepods – while further chapters consider molluscs and, as promised in the title, leeches and lampreys.

There is rich diversity in this spectrum of different phyla associated with the outsides of fishes. The final chapter summarizes this range with respect to reproduction, attachment, feeding, host and site specificity, pathogenic and immune interactions. There is vivid demonstration of the inventiveness of parasitic adaptations – the incredibly complex jaw-like clamps of some monogeneans operated by a system of muscles, tendons, fairleads and pulleys. In Argulus, the crustacean limb, the first maxilla, has been transformed into a powerful sucker, but the steps involved in this evolutionary change defy the imagination. In this concluding chapter, Kearn emphasizes the numerical dominance of crustaceans and the enormous diversity of their parasitic associations. This is the area familiar in older textbooks of ‘classical’ parasitology where readers may marvel at bizarre inventions, especially with regard to sex. Thus, some cymothoids change sex during life and the presence of one sex determines the sexual development of colleagues; loss of a female from the host results in males becoming female. Chondracanthid copepods have diminutive males attached to the female and probably parasitic on her. All this makes one wonder whether application of modern research techniques to these parasites might uncover fundamental principles about sex determination, developmental regulation and tissue differentiation.

The preface outlines the remit “to produce a well-structured text that is up-to-date and sufficiently informative to satisfy the professional biologist, whilst comprehensive and interesting for the enquiring amateur”. The book succeeds in all of this, and specialist parasitologists interested in ectoparasites and fish will find both a rich vein of new information and a satisfying review of well-established (“classic”) knowledge. The descriptive style produces a thoughtful, flowing narrative with an obvious fascination for detail. There is no concession to simplification or popularization for the “enquiring amateur”; the overviews represent a top-class discussion by a leading authority of this research field. The descriptive accounts benefit from the author's extensive knowledge of the history of his field and of the literature, much of it out-of-reach to present-day readers, where remarkable insight was obtained by careful microscope observation. The author's approach creates encyclopaedic coverage of the broad field. Much will be learnt about parasites largely unknown to non-specialists, while for parasites with which readers may have a general acquaintance this book provides meticulous detail; thus, the common fish louse, Argulus, is given a 27 page chapter. Particularly satisfying for the many parasite biology courses that cite Entobdella as a “type example”, a 24-page chapter includes a comprehensive review bringing together the author's findings published since the early 1960s that make this the most intensively studied of monogeneans.

The book's subtitle “A natural history of … parasites” allows Kearn to range comprehensively across all aspects of the biology of the organisms within his remit; but, it should not be taken to suggest a general readership. Thus, there is a bibliography of 43 pages (with nearly 600 references) that is up-to-date and very valuable to researchers venturing across diverse fields. The thoroughness of approach is also reflected in detailed indices (another 14 pages), appendices of names of hosts and parasites (12 pages), and a comprehensive glossary of scientific terms (9 pages). An attractive and informative feature of this book, following the tradition of all Kearn's publications, is the wealth of illustrations. Most are Kearn's own line drawings, while many of those taken from other sources have been redrawn, giving a pleasing uniformity. The publishers have made an excellent job of production.

Lecturers in general parasitology and wider aspects of zoology, and students in search of essay material, will find a rich synthesis of “special interest topics”, such as circadian rhythms, host specificity, convergent evolution, symmetry, and many others. This is a work of great scholarship.