image: This is a frontal view on computed tomography scans of female and male eels in different maturation stages displaying successive loss of bone with progressing maturation view more
Credit: Larissa Yokota Rizzo and Marko Freese
A study charts body transformation in European eels during their 6,000-km-long journey to spawn in the open ocean. The European eel (Anguilla anguilla), a critically endangered species, embarks on an arduous transoceanic journey to reproduce once in its lifespan. Adults spawn in the open ocean, and the larvae are transported to inland and coastal waters, where the eels grow and mature into adults. With the onset of puberty, the eels change in appearance from pale yellow to gleaming silver--a process termed silvering--before returning to spawn in the ocean. On the return trip, the eels undergo drastic changes: they stop feeding, shrink their guts, break down their skeletons, and build up their gonads. Marko Freese, Larissa Yokota Rizzo, and colleagues used hormone treatments to artificially mature the eels in the laboratory, and monitored the breakdown of the eels' skeletons and resulting redistribution of minerals during maturation. Using analytical and imaging techniques, the authors found that the eels' average bone mass and mineral content declined with the onset of silvering, potentially compromising mechanical support offered by the vertebrae while sparing the function of the notochord. Bone loss was more pronounced in females than males. The proportion of phosphorus and calcium in soft tissues versus bone increased as maturation progressed, indicating that the eels use their bones and muscles as energy and mineral reserves for locomotion and spawning. Moreover, the authors detected the transfer of an array of metals--cadmium, copper, manganese, and mercury--from bones and soft tissues to the ovaries of gravid silver eels. The latter finding suggests that the metals, known to generate toxic free radicals, might hamper the eels' reproductive success and raises the specter of potential anthropogenic impacts on the eels' freshwater habitats. According to the authors, the findings provide a window into the molecular processes underlying dramatic body reorganization in a species of conservation concern.
Article #18-17738: "Bone resorption and body reorganization during maturation induce maternal transfer of toxic metals in anguillid eels," by Marko Freese et al.
MEDIA CONTACT: Marko Freese, Thünen Institute of Fisheries Ecology, Federal Research Institute for Rural Areas, Forestry, and Fisheries, Bremerhaven, GERMANY; tel: +49 471 94460131; e-mail: Marko.Freese@thuenen.de
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Journal
Proceedings of the National Academy of Sciences