[1] Yarrell had the free time and income to indulge his hobbies of shooting and fishing, and started to show an interest in rare birds, sending some specimens to the engraver and author Thomas Bewick.

[1] Interest in natural history was growing rapidly in the early nineteenth century, and several writers sought to provide definitive lists of species found in Britain, with descriptions and other pertinent information.

[5] The most notable foreign sources were the Histoire naturelle des poissons (1828–1831) by Baron Georges Cuvier and Achille Valenciennes, which contained descriptions of five thousand species of fishes, and Marcus Elieser Bloch's beautifully illustrated twelve-volume Allgemeine Naturgeschichte der Fische (1782–1795).

[6][a] Yarrell was a keen fisherman, and his journeys to English south coast locations like Brighton, Weymouth and Hastings gave him direct access to fresh specimens.

[9][c] As a London-based bookseller and an active member of London's learned societies, Yarrell had contact with many fellow naturalists who could help him with books, illustrations and notes, as well as specimens.

He was a life-long friend of clergyman naturalist Leonard Jenyns, and a regular correspondent with the taxidermist John Gould, Sir William Jardine,[10] the Earl of Derby, Edward Lear and Charles Darwin.

[11][12] Yarrell's knowledge of avian anatomy helped Lear develop his bird painting skills by teaching him that feather tracts follow the muscle contours, and he in return provided a drawing of a thicklip grey mullet for the fish book.

[13][14] Yarrell made significant discoveries of his own, including showing that male seahorses and pipefish carried fertilised eggs in a pouch,[3] and clarifying how many Salmo (salmon and trout) species occurred in Britain.

[18][d] Volume 1 has a preface which also acknowledges the people who had helped Yarrell with his project, followed by an introduction discussing the general characteristics of fish (fifteen pages in the first edition) and an alphabetical index before the main species accounts start.

There was no established taxonomic sequence for arranging fish, so where possible Yarrell followed Cuvier and Valenciennes, otherwise using anatomical resemblances in features including fins, teeth, and head bones to order his species.

[22] Each entry started with a wood engraving of the species, followed by its scientific and English names and their synonyms, and a lead section "Generic characteristics" summarising the key anatomical features.

As well as the expected detailed anatomical and geographical information, in the five-page text he notes: In rivers, the Perch prefers the sides of the stream rather than the rapid parts of the current, and feeds indiscriminately upon insects, worms, and small fishes ...

[25][26] The most expensive part of producing illustrated books in the nineteenth century was the hand colouring of printed plates,[27] mainly by young women.

[29] Yarrell's many other ichthyological works included an 1839 three-page, 30.5 by 44 cm (12.0 by 17.3 in) oblong folio, On the Growth of the Salmon in Fresh Water, with drawings in the text and six life-sized coloured illustrations of the fish, chapter 8, "Marine Fishes", in William Henry Harvey's 1854 The Sea-Side Book,[29] and an article on Eurasian dace in the Transactions of the Linnean Society of London.

Near the end of a 35-page review, it states This book ought to be largely circulated, not only on account of its scientific merits – though these, as we have in part shown, are great and signal – but because it is popularly written throughout, and therefore likely to excite general attention to a subject which ought to be held as one of primary importance by all those gentlemen of education and property who happen to be more immediately connected with some of the most extensive, and which might be among the most useful and important, districts of this empire.The passage continues with the promotion of sea fish as a means to relieve famine.