Inside the Fish Skin Collection: Ollie Crimmen and the Lost Radiographs

Oliver (Ollie) Crimmen, Senior Fish Curator at the Natural History Museum, has been the Honorary Curator of Fish and Shells at the Linnean Society since 2017. As he retires from his post at the NHM, we would like to thank him for all his voluntary work at the Linnean Society. He has helped us look after the collections of Linnaeus' shells and fish, curating the collection and dealing with scientific enquiries and visits. Along with the three other honorary curators, he has been part of our Collections Committee, helping us with our Collections strategy and giving us advice on curation and the sometimes tricky environmental conditions in our lovely but old building. Ollie presented on the Linnean Society's fish in our Linnean Lens series, when he memorably brought the wet specimen of a sharksucker to contrast it with the Linnaean dried specimen.

We are extremely privileged to work with Ollie, to benefit from his extensive knowledge and his calm and measured advice. Fortunately, Ollie is staying at the NHM as an associate and as our Honorary Curator for a little while longer, and we look forward to continuing our collaboration with him.

In the 1970s, a series of X-rays were completed at the bequest of Peter Whitehead, a Curator of Fishes at the Natural History Museum, as well as the Curator of Fish for the Linnean Society. He tasked the newly appointed assistant curator, Oliver Crimmen, to X-ray the full series of 168 Linnaean fish specimens. Ollie, now the Linnean Society’s soon-to-be-retired Curator of Fish and Shells, recalls his first few weeks on the job, spent in the dark basement radiography room. However, once completed, the X-rays failed to make their way to their intended home in the Linnean Society collections, instead finding themselves lost to the expansive archives of the Natural History Museum.

The storerooms of the Natural History Museum are a collector’s paradise. Everything that has ever made its way into the museum remains carefully arranged in a maze of rooms full of crates, boxes, cabinets, and jars. During recent renovation works, decades of untouched boxes were rummaged through for hidden treasures, and by happenstance the Linnaean Fish Skin X-ray series was rediscovered. These radiographs have now been digitised, and both the digital images and the X-rays have been returned to the Linnean Society.

Radiographs give us unique insight into not only the anatomy of fishes but also the preservation techniques used in historic collections. Modern preservation practises, such as those used by the Natural History Museum, favour a fluid preservation technique.

This technique involves fixing the tissue with formalin and then transferring it to an alcohol preservative for long term storage. Fluid preservation best preserves the whole anatomy of the fish for further study, but historically a ‘dry skin’ preservation method was preferred. This involved removing the skin from one side of the fish, drying it and then preserving it with varnish. Sadly, much of the distinctive anatomy of any specimen was lost when this method was used.

The radiographs of Carl Linnaeus' fishes reveal for the first time some of the internal structures not visible from the dry specimen. A radiograph of the Greater Pipefish, Syngnathus acus (LINN 49), shows the highly modified skeleton and bony armour that is so characteristic of the genus. It also reveals the extent of damage done during the preservation process: some of the delicate vertebrae have been scraped off when the skin was removed.

Removal of the internal structure is an unfortunate downside of the dry skin preparation method. A scan of a Smooth Butterfly Ray, Gymnura micrura (LINN 129), shows where the radial cartilage has been removed, but the skull and spine have been preserved.

The only full taxidermy, as opposed to dried, specimen in the Linnaean collection is a Hogchoker, Trinectes maculatus (LINN 123). The taxidermy preservation has prevented much of the internal structure, like the spine and ribs, from being preserved so little additional data can be revealed with an X-ray. However, the radiograph reveals what is hard to appreciate with the naked eye: an intricate and complex lattice of scales.

Radiographs provide a novel and captivating aesthetic perspective into these scientific collections. Linnaeus’ collection represents a remarkable contribution to ichthyology and these X-rays offer an additional insight into a previously unknown dimension of the collection. And now, with these X-rays being reunited with the Linnean Society, they will be treated as a treasure in their own right.

Chrissy Williams, Curatorial Assistant, Fish, Natural History Museum

chrissy.williams1@nhm.ac.uk