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Marine Biology

, Volume 156, Issue 5, pp 835–846 | Cite as

Positive buoyancy in eel leptocephali: an adaptation for life in the ocean surface layer

  • Katsumi Tsukamoto
  • Yoshiaki Yamada
  • Akihiro Okamura
  • Toyoji Kaneko
  • Hideki Tanaka
  • Michael J. Miller
  • Noriyuki Horie
  • Naomi Mikawa
  • Tomoko Utoh
  • Satoru Tanaka
Original Paper

Abstract

Many planktonic organisms have adaptations such as floats or lighter substances to obtain buoyancy to help them remain in the surface layer of the ocean where photosynthetic primary production occurs and food is most abundant. The almost totally transparent eel larvae, called leptocephali, are a unique member of the planktonic community of the surface layer, but their ecology and physiology are poorly understood. We conducted a comparative study on the specific gravity of planktonic animals including 25 taxa of 7 phyla of marine invertebrates and 6 taxa of leptocephali (vertebrate) to gain a broad perspective on the buoyancy of the eggs and larval stages of the Japanese eel. The specific gravity values of the various freshly caught marine invertebrate taxa varied widely from 1.020 to 1.425, but leptocephali had some of the lowest values (1.028–1.043). Artificially cultured live leptocephali had even greater buoyancies with specific gravities of 1.019–1.025 that were close to or lower than seawater, and their buoyancy showed ontogenetic changes among the different early life history stages. Leptocephali appear to have a unique mechanism of buoyancy control by chloride cells all over body surface through osmoregulation of body fluid contained in the extracellular matrix of transparent gelatinous glycosaminoglycans filling their bodies. This adaptation is likely a key factor for their survival by helping them to remain in the surface layer where food particles are the most abundant, while being transparent for predator avoidance. The ontogenetic change in buoyancy of eel eggs, leptocephali and glass eels likely enhances their larval survival, transport, and recruitment to terrestrial freshwater habitats.

Keywords

Specific Gravity Early Life History Chloride Cell High Specific Gravity North Equatorial Current 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgments

We thank the captain and crew of the R/V Hakuho Maru for assistance in making the plankton collections, the other scientists onboard for assistance in collecting and sorting the plankton samples, and T. Horita, curator of the Toba Aquarium, for kindly providing us a reared moon jelly.

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Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  • Katsumi Tsukamoto
    • 1
    • 2
  • Yoshiaki Yamada
    • 2
  • Akihiro Okamura
    • 2
  • Toyoji Kaneko
    • 3
  • Hideki Tanaka
    • 4
  • Michael J. Miller
    • 1
  • Noriyuki Horie
    • 2
  • Naomi Mikawa
    • 2
  • Tomoko Utoh
    • 2
  • Satoru Tanaka
    • 2
  1. 1.Ocean Research InstituteThe University of TokyoTokyoJapan
  2. 2.IRAGO Institute Co., Ltd.TaharaJapan
  3. 3.Department of Aquatic Bioscience, Graduate School of Agricultural and Life SciencesThe University of TokyoTokyoJapan
  4. 4.Fisheries Research AgencyNational Research Institute of AquacultureMinamiiseJapan

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