title: Lubricating the swordfish head.
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.
authors.affiliation: Prof. Em. Groningen & Leiden University, Zuidlaarderweg 57, Noordlaren 9479 TH, The Netherlands j.j.videler@rug.nl.
authors.forename: John J
authors.identifier: 0000-0003-1226-9528
authors.initials: JJ
authors.lastname: Videler
authors.affiliation: Faculty of Behavioural and Social Sciences, University of Groningen, Grote Kruisstraat 2/1, Groningen 9712 TS, The Netherlands.
authors.forename: Deniz
authors.initials: D
authors.lastname: Haydar
authors.affiliation: Waterproof, Marine Consultancy & Services BV, Flevo Marina Trade Centre, IJsselmeerdijk 2, Lelystad 8221 RC, The Netherlands.
authors.forename: Roelant
authors.initials: R
authors.lastname: Snoek
authors.affiliation: GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, Kiel D-24105, Germany.
authors.forename: Henk-Jan T
authors.initials: HJ
authors.lastname: Hoving
authors.affiliation: Faculty of Medical Sciences, Groningen University, Institute for Medical Education, Antonius Deusinglaan 1, Groningen 9713 AV, The Netherlands.
authors.forename: Ben G
authors.initials: BG
authors.lastname: Szabo
mesh_terms: D000818:Animals; D005088:Exocrine Glands / Q000648:ultrastructure; D017276:Friction; D006257:Head / Q000033:anatomy & histology; D057927:Hydrophobic and Hydrophilic Interactions; D008279:Magnetic Resonance Imaging; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D010473:Perciformes / Q000033:anatomy & histology* / Q000502:physiology*; D012867:Skin / Q000648:ultrastructure; D013550:Swimming
keywords: Drag reduction; Functional morphology; Oil gland; Porous skin; Swordfish