The Murky Waters of Classification: Ordering Fish in Eighteenth-century Europe

By Didi van Trijp

‘Fish & Fiction‘ is an exhibition on the history of fascination with the aquatic life, between 1500-1900, and is currently on show at the University Library of Leiden University (until January 13). The coming weeks Shells and Pebbles is publishing some of the catalogue texts, composed by the historians who contributed to the exhibition, and which previously appeared on the Leiden Arts in Society Blog.  This week  we publish a blog by Didi van Trijp, about the insatiable thirst of 18th century naturalists for order in the animal kingdom, stretching from mermaids to whales, and from Prussia to Brazil. 

Fishes had been subject to categorization from the sixteenth century onwards, although in this period various taxonomical principles could co-exist at the same time. Approaches towards ordering nature changed significantly in the late seventeenth and early eighteenth centuries. This can be seen, for example, in the fish book Historia piscium (Oxford, 1686) written by the English naturalists Francis Willughby and John Ray. Their book offered a precise definition of a fish: namely an aquatic animal, lacking feet, with either naked skin or scales, swimming by means of fins, living perpetually in the water, and never of its own volition coming out onto dry land. This definition narrowed the scope of what they thought should be included in a fish book – and what should be left out.

This wish to define and demarcate also drove later naturalists. Especially the Swedish naturalists Peter Artedi (1705–1735) and Carolus Linnaeus (1707–1778) seemed to have an insatiable thirst for order. Artedi devised a system in which all fish species could be grouped into genera, families, orders and classes. He stated that an ichthyologist should look for specific characteristics that distinguished certain groups of fish species from others, such as the number of fins, the position of the fins, and the numbers of rays in the fins. By paying close attention to external characteristics a naturalist could unravel the structure and design of the natural world. Artedi used this new approach to the study of fishes in a book entitled Ichthyologia (Leiden, 1738) published posthumously by his close friend Linnaeus.

Fig. 1 | Philosophia ichthyologia, in Peter Artedi, Ichthyologia sive opera omnia de piscibus, sc. Bibliotheca ichthyologica, philosophia ichthyologica … recognavit, coapt. et edidit Car. Linnaeus, Leiden, C. Wishoff, 1738, p. 1.

In the Ichthyologia, Artedi unfolded his philosophy of fish and his rules for the study of those fish. The book contains no images, only short descriptions of the characteristics that Artedi deemed pertinent for classification. As a result, the book is of a manageable octavo format.

Although Artedi died prematurely by drowning in an Amsterdam canal, his work effected a lasting change in the way that naturalists organised fish species. Linnaeus’s legacy was even greater. He established genera, families, order and classes for the three natural kingdoms of animals, plants and minerals. He also introduced the binomial system still in use today. This meant that species names consisted of a genus and a species name, rather than of the short diagnostic sentences that were used as species names until that time. His Systema naturae (Leiden, 1735) offered a first systematic account based on these principles.

Fig. 2 | Table of the animal kingdom, in Carolus Linnaeus, Systema naturae, sive regna tria naturae systematice proposita per classes, ordines, genera, et species, Leiden, T. Haak, 1735. [1372 F 4]

Linnaeus ordered the three kingdoms of nature (animals, plants and minerals) in nicely ordered tables in Systema naturae The division of the fishes in this edition of the book was borrowed from the system that Artedi had devised. Linnaeus also included a category of paradoxa, for animals of whose existence he was not quite certain. The classification system also provoked criticism. The Parisian naturalist Comte du Buffon called it arbitrary and artificial, a discourtesy to the diversity and richness of nature. Nonetheless, the standardization of species names facilitated communication between naturalists.

Some aquatic animals, however, resisted clear-cut classification. One of these impervious creatures was the mermaid. Stories of mermaid sightings circulated from Antiquity onwards and surfaced throughout the early modern period. Reports of mermaid sightings also remained quite common in the eighteenth century, often celebrated as the great age of reason. One such report can be found in François Valentijn’s (1666–1727) account of Ambon Oud en Nieuw Oost-Indiën (Amsterdam, 1727). The Zeewijf van Buru (sea-woman of Buru) was described and depicted by the Dordrecht vicar in this account of Ambon. The original drawing of this mermaid was made by the physician Samuel Fallours. A later, and somewhat altered rendering of this mermaid appears in Louis Renard’s Poissons, Ecrévisses et Crabes (Amsterdam, 1754).

One could, however, also glimpse sight of a mermaid closer to home. Upon reading reports of mermaid sightings in Stockholm newspapers in 1749, Linnaeus wrote to the Swedish Academy of Science and urged them to try and catch this creature alive, or else preserve it in spirits. In one of his notebooks, Linnaeus listed the mermaids under the humans and the apes. In the second edition of the Systema naturae (1740) he adopted the mermaid into his category of paradoxa, together with other complex beings such as the satyr.

Other naturalists, notably Artedi, grouped mermaids among the whales. But were whales, in turn, even fish? This too was subject to debate. Whales and other cetaceans had long been lumped together with the fishes, and for good reasons. The definition of a fish that Willughby and Ray drafted, for example, also applied to the whale. It was Linnaeus who decided that whales should be grouped with the mammals rather than with fishes on the basis of their internal similarities. This change was published in the tenth edition of the Systema naturae (1758), today considered to be the most authoritative version of this work. Linnaeus’ decision to divorce the cetaceans from the fishes was adopted by a fair share of naturalists, but in practice whales often continued to be considered fishes, at least outside academic circles.

Despite these ambiguities many naturalists actually took to the Linnaean system. They applied the method to fishes observed in their home region as well as to fish encountered in foreign, faraway regions. The Berlin physician Marcus Élieser Bloch (1723–1799) had a passion for the natural history of fishes. Bloch set out to collect, describe, compile and publish an overview of the fishes of the Prussian states because he found his copy of Linnaeus lacking descriptions of even some of the most common fish species existing in those states. His research resulted in the lavishly illustrated twelve-volume Allgemeine Naturgeschichte der Fische (Berlin, 1782–1795).

Fig. 4 | C.F. Gürsch, Porpoise, in Marcus Élieser Bloch, Ichthyologie ou histoire naturelle et particulière des poissons, Berlin, ‘chez l’auteur’ and F. de La Garde, 1795–1797), plates parts 1-4, plate 92. [137 A 1-6]

The twelve-volume Allgemeine Naturgeschichte der Fische by Bloch was one of the first wide-ranging ichthyological works based on Linnaean principles. He included the porpoise that could be sighted on the German coasts in this survey, even if Linnaeus has already ruled that it should be classed among the mammals. This illustration (fig. 4) comes from the French translation of the work that the author published.

Drawing on his connections with fellow naturalists as well as on contacts with travellers such as missionaries, Bloch managed to amass thousands of fish specimens. His fish collection grew to encompass not only fishes from the German states, but, also what he called ‘foreign’ fishes. As a result of the ongoing European expansion, he managed to describe fishes from i.a. the Americas, East-Indies, India and Africa. Like many other naturalists, he soon found that he could not fit all these species into the genera that Artedi and Linnaeus had established and therefore needed to create new categories. He also included the porpoise in his ichthyological oeuvre, and thus did not follow all of the taxonomic rules proposed by Linnaeus.

Fig. 5 | J.F. Hennig, Brazilian Wrasse, in Marcus Élieser Bloch, Ichthyologie ou histoire naturelle et particulière des poisons, Berlin, ‘chez l’auteur’ and F. de La Garde, 1795–1797, plates parts 5-8, plate 280

Bloch boasted a fish collection that allegedly encompassed over a thousand specimens. Many of these fish came from beyond European borders and were sent to them by his wide-ranging correspondents. This illustration of a Brazilian wrasse, however, is based on a drawing of the species in Marcgraf and Piso. The engraver and artist J.F. Hennig made this image and added the exuberant colouration.

The emergence of classificatory systems resulted in sharply articulated definitions and a standardization in naming practices. Yet also within this seemingly stable system, rules and categories shifted. The Systema naturae remained under continuous revision, and naturalists ignored, altered or added rules to the system that this seminal work unfolded. The emphasis on classification also signalled a shift towards increasing specialization, as not only the natural world but also the world of knowledge itself was divided into an increasing number of categories.