ABSTRACT
The swordfish is reputedly the fastest swimmer on Earth. The concave head and iconic sword are unique characteristics, but how they contribute to its speed is still unknown. Recent computed tomography scans revealed a poorly mineralised area near the base of the rostrum. Here we report, using magnetic resonance imaging and electron microscopy scanning, the discovery of a complex organ consisting of an oil-producing gland connected to capillaries that communicate with oil-excreting pores in the skin of the head. The capillary vessels transport oil to abundant tiny circular pores that are surrounded by denticles. The oil is distributed from the pores over the front part of the head. The oil inside the gland is identical to that found on the skin and is a mixture of methyl esters. We hypothesize that the oil layer, in combination with the denticles, creates a super-hydrophobic layer that reduces streamwise friction drag and increases swimming efficiency.
FOOTNOTES
Competing interests
The authors declare no competing or financial interests.
Author contributions
J.J.V. is the initiator of the swordfish project of the former department of Marine Biology of Groningen University. R.S. discovered the capillary network during his master’s project. D.H. and H.-J.T.H. prepared and analysed SEM pictures of the pores in the skin. B.G.S. initialised and supervised the MRI procedure.
Funding
This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.
Supplementary information
Supplementary information available online at http://jeb.biologists.org/lookup/suppl/doi:10.1242/jeb.139634/-/DC1
- Received February 29, 2016.
- Accepted April 17, 2016.
- © 2016. Published by The Company of Biologists Ltd
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