title: How the European eel (Anguilla anguilla) loses its skeletal framework across lifetime.
abstract: European eels (Anguilla anguilla) undertake an impressive 5 000 km long migration from European fresh waters through the North Atlantic Ocean to the Sargasso Sea. Along with sexual maturation, the eel skeleton undergoes a remarkable morphological transformation during migration, where a hitherto completely obscure bone loss phenomenon occurs. To unravel mechanisms of the maturation-related decay of the skeleton, we performed a multiscale assessment of eels' bones at different life-cycle stages. Accordingly, the skeleton reflects extensive bone loss that is mediated via multinucleated bone-resorbing osteoclasts, while other resorption mechanisms such as osteocytic osteolysis or matrix demineralization were not observed. Preserving mechanical stability and releasing minerals for energy metabolism are two mutually exclusive functions of the skeleton that are orchestrated in eels through the presence of two spatially segregated hard tissues: cellular bone and acellular notochord. The cellular bone serves as a source of mineral release following osteoclastic resorption, whereas the mineralized notochord sheath, which is inaccessible for resorption processes due to an unmineralized cover layer, ensures sufficient mechanical stability as a part of the notochord sheath. Clearly, an eel's skeleton is structurally optimized to meet the metabolic challenge of fasting and simultaneous sexual development during an exhausting journey to spawning areas, while the function of the vertebral column is maintained to achieve this goal.
authors: Department of Osteology and Biomechanics, University Medical Center Hamburg-Eppendorf, Lottestr. 59, 22529 Hamburg, Germany.
authors: Tim
authors: T
authors: Rolvien
authors: Gesellschaft für Marine Aquakultur mbh, Hafentörn 3, 25761 Büsum, Germany.|Aller Aqua Research GmbH, Hafentörn 3, 25761 Büsum, Germany.
authors: Florian
authors: F
authors: Nagel
authors: Department of Osteology and Biomechanics, University Medical Center Hamburg-Eppendorf, Lottestr. 59, 22529 Hamburg, Germany.|Laboratory for Anthropology, Institute of Anatomy, Faculty of Medicine, University of Belgrade, Dr Subotica 4/2, 11000 Belgrade, Serbia.
authors: Petar
authors: P
authors: Milovanovic
authors: Leibnitz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587 Berlin, Germany.
authors: Sven
authors: S
authors: Wuertz
authors: Department of Osteology and Biomechanics, University Medical Center Hamburg-Eppendorf, Lottestr. 59, 22529 Hamburg, Germany.
authors: Robert Percy
authors: RP
authors: Marshall
authors: Department of Osteology and Biomechanics, University Medical Center Hamburg-Eppendorf, Lottestr. 59, 22529 Hamburg, Germany.
authors: Anke
authors: A
authors: Jeschke
authors: Department of Osteology and Biomechanics, University Medical Center Hamburg-Eppendorf, Lottestr. 59, 22529 Hamburg, Germany.
authors: Felix N
authors: FN
authors: Schmidt
authors: Department of Osteology and Biomechanics, University Medical Center Hamburg-Eppendorf, Lottestr. 59, 22529 Hamburg, Germany.
authors: Michael
authors: M
authors: Hahn
authors: Department of Biology, Research Group Evolutionary Developmental Biology, Ghent University, Ledeganckstraat 35, 9000 Ghent, Belgium.
authors: P Eckhard
authors: PE
authors: Witten
authors: Department of Osteology and Biomechanics, University Medical Center Hamburg-Eppendorf, Lottestr. 59, 22529 Hamburg, Germany.
authors: Michael
authors: M
authors: Amling
authors: Department of Osteology and Biomechanics, University Medical Center Hamburg-Eppendorf, Lottestr. 59, 22529 Hamburg, Germany b.busse@uke.de.
authors: Björn
authors: 0000-0002-3099-8073
authors: B
authors: Busse
mesh_terms: D000811:Anguilla / Q000033:anatomy & histology* / Q000502:physiology; D025041:Animal Migration; D000818:Animals; D001267:Atlantic Ocean; D001862:Bone Resorption; D001842:Bone and Bones / Q000502:physiology*; D002113:Calcification, Physiologic; D008018:Life Cycle Stages
keywords: European eel; bone loss; osteoclasts; spawning migration