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In situ swimming behavior of the Mariana snailfish Pseudoliparis swirei

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Abstract

The hadal zone, defined as ocean depths below 6000 m, is one of Earth’s most extreme environments. The Mariana snailfish Pseudoliparis swirei is among the deepest known fishes, yet its natural behavior remains largely unknown. Here we quantify, for the first time, the three-dimensional swimming behavior of this species in its native habitat by analyzing video collected by a baited deep-sea lander at nearly 7000 m depth. Using an automated computer vision workflow that detects, tracks and infers visual depth from single camera footage, we reconstructed full trajectories for individual fish using 868 manually annotated instances. The results show that P. swirei exhibits a slow routine swimming speed of 0.16-0.18 m s⁻1 (0.62-0.80 body lengths s⁻1, mean ≈ 0.71 BL s⁻1), with low variability across individuals and only short acceleration events reaching up to ~ 0.50 m s⁻1. By combining reconstructed movement paths with a simple representation of near bottom flow, we estimate that the fish operates within a modest spatial range around the bait. A mechanistic advection-diffusion framework further indicates that P. swirei first detects bait odor at a distance of approximately 350 m. These findings provide the first quantitative view of locomotion in a hadal vertebrate, revealing gentle, steady gaits shaped by environmental constraints.

Data availability

The computer-vision analysis pipeline used for fish detection, monocular depth estimation, trajectory reconstruction, and swimming-speed calculation is openly available on GitHub at: https://github.com/chenyizi65/FishSpeed. The repository contains the scripts and configuration files required to reproduce the analyses. Data generated during this study are derived from deep-sea lander video recordings and processed outputs produced using this pipeline. Representative data are included in the manuscript and Supplementary Information.

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Acknowledgements

This work was supported by the project 2025YFE0218900. We are grateful to R/V Tansuo Yihao for their contributions in lander deployment.

Funding

This study was supported by National Natural Science Foundation of China (42376149) and Shenzhen Key Laboratory of Advanced Technology for Marine Ecology (ZDSYS20230626091459009).

Author information

Author notes

  1. These authors contributed equally: Yizi Chen and Alexandru S. Barcan.

Authors and Affiliations

  1. Institute for Ocean Engineering, Shenzhen International Graduate School, Tsinghua University, Shenzhen, 518055, China

    Yizi Chen, Alexandru S. Barcan, Jiushuang Zhang & Yong Wang

  2. Shenzhen Key Laboratory of Advanced Technology for Marine Ecology, Shenzhen International Graduate School, Tsinghua University, Shenzhen, 518055, China

    Jiushuang Zhang & Yong Wang

  3. Institute of Deep-Sea Science and Engineering, Chinese Academy of Sciences, Sanya, 572000, Hainan, China

    Jun Li

  4. Dongguan Institute of Technology, Dongguan, 523808, Guangdong, China

    Lisheng He

Authors

  1. Yizi Chen
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  2. Alexandru S. Barcan
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  3. Jiushuang Zhang
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  4. Jun Li
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  5. Lisheng He
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  6. Yong Wang
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Contributions

A.S.B. analyzed the data and wrote the first draft of the manuscript. Y.C. performed the video analysis, frame-based calculations, and prepared the figures. J.Z., J.L., L.H., and A.S.B. reviewed the manuscript. Y.W. conceived the study.

Corresponding author

Correspondence to
Yong Wang.

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The authors declare no competing interests.

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Supplementary Information

Supplementary Information 1. (download DOCX )

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Chen, Y., Barcan, A.S., Zhang, J. et al. In situ swimming behavior of the Mariana snailfish Pseudoliparis swirei.
Sci Rep (2026). https://doi.org/10.1038/s41598-026-48409-2

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  • DOI: https://doi.org/10.1038/s41598-026-48409-2

Keywords

  • Snailfish
  • Hadal trench
  • Swimming speed
  • Deep-sea fish
  • Biomechanics

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