Buoyancy and hydrostatic balance in a West Indian Ocean coelacanth Latimeria chalumnae

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Background: Buoyancy and balance are important parameters for slow-moving, low-metabolic, aquatic organisms. The extant coelacanths have among the lowest metabolic rates of any living vertebrate and can afford little energy to keep station. Previous observations on living coelacanths support the hypothesis that the coelacanth is neutrally buoyant and in close-to-perfect hydrostatic balance. However, precise measurements of buoyancy and balance at different depths have never been made. Results: Here we show, using non-invasive imaging, that buoyancy of the coelacanth closely matches its depth distribution. We found that the lipid-filled fatty organ is well suited to support neutral buoyancy, and due to a close-to-perfect hydrostatic balance, simple maneuvers of fins can cause a considerable shift in torque around the pitch axis allowing the coelacanth to assume different body orientations with little physical effort. Conclusions: Our results demonstrate a close match between tissue composition, depth range and behavior, and our collection-based approach could be used to predict depth range of less well-studied coelacanth life stages as well as of deep sea fishes in general.

TidsskriftBMC Biology
Antal sider20
StatusUdgivet - 2022

Bibliografisk note

Funding Information:
HL was funded by the Lundbeck Foundation (R324-2019–1470), the Velux Foundations (00022458), and the Carlsberg Foundation (CF21-0605) during the making of this study. The project was not specifically funded.

Funding Information:
We wish to acknowledge Jørgen Gissel Nielsen, Natural History Museum of Denmark, University of Copenhagen, for honoring the original agreement with the Muséum National d’Histoire Naturelle, Paris, that the coelacanth specimen (CCC 23) received as a gift in Copenhagen in 1962 was to remain intact and not be further dissected. This allowed for the present non-invasive study on the intact specimen as well as future work using techniques that we have so far not considered or perhaps currently do not exist. Also, we wish to thank the Department of Forensic Medicine, Aarhus University (AU), specifically Lene Warner Thorup Boel, Kasper Hansen, and Christina Caroe Ejlskov Pedersen, for kindly providing access to the CT system and providing aid during scanning. We also wish to thank the Clinic for Osteoporosis, Hormone and Bone Diseases, Aarhus University Hospital, specifically Lars Rejnmark and Tove Stenum for providing access to the extremity CT system used to image smaller species. Likewise, we wish to thank the MR-research center (AU) specifically Christoffer Laustsen for providing affordable access to MRI. We also wish to thank Jesper Skovhus Thomsen (AU) for help with preliminary experiments on bone mineral estimation and ashing. We wish to thank Kristina Ydesen (The North Sea Oceanarium) for providing access to the beached Mola mola. Additionally, we wish to thank Anita Dittrich (AU) and Mette Dalgaard (AU) for providing help with colorimetric assays. Finally, we wish to thank Thomas Desvignes (University of Oregon), H William Detrich (Northeastern University), Christian Damsgaard (AU), Tobias Wang (AU), and Michael Pedersen (AU) for invaluable discussions on buoyancy in fish and image analysis.

Publisher Copyright:
© 2022, The Author(s).

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