title: Kinematics of mouthbrooding in Oreochromis niloticus (Cichlidae).
abstract: Many species from several different families of fishes perform mouthbrooding, where one of the sexes protects and ventilates the eggs inside the mouth cavity. This ventilation behaviour differs from gill ventilation outside the brooding period, as the normal, small-amplitude suction-pump respiration cycles are alternated with actions including near-simultaneous closed-mouth protrusions and high-amplitude depressions of the hyoid. The latter is called churning, referring to its hypothetical function in moving around and repositioning the eggs by a presumed hydrodynamic effect of the marked shifts in volume along the mouth cavity. We tested the hypothesis that churning causes the eggs located posteriorly in the mouth cavity to move anteriorly away from the gill entrance. This would prevent or clear accumulations of brood at the branchial basket, which would otherwise hinder breathing by the parent. Dual-view videos of female Nile tilapias (Oreochromis niloticus) during mouthbrooding showed that churning involves a posterior-to-anterior wave of expansion and compression of the head volume. Flow visualisation with polyethylene microspheres revealed a significant inflow of water entering the gill slits at the zone above the pectoral fin base, followed by a predominantly ventral outflow passing the ventrolaterally flapping branchiostegal membranes. X-ray videos indicated that particularly the brood located close to the gills is moved anteriorly during churning. These data suggest that, in addition to mixing of the brood to aid its oxygenation, an important function of the anterior flow through the gills and buccal cavity during churning is to prevent clogging of the eggs near the gills.
authors.affiliation: Department of Biology, University of Antwerp, Universiteitsplein 1, Antwerpen 2610, Belgium Department of Biology, Ghent University, K.L. Ledeganckstraat 35, Gent 9000, Belgium sam.vanwassenbergh@uantwerpen.be.
authors.forename: Sam
authors.initials: S
authors.lastname: Van Wassenbergh
authors.affiliation: Department of Biology, University of Antwerp, Universiteitsplein 1, Antwerpen 2610, Belgium.
authors.forename: Iris
authors.initials: I
authors.lastname: Joris
authors.affiliation: Department of Biology, University of Antwerp, Universiteitsplein 1, Antwerpen 2610, Belgium.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Desclée
authors.affiliation: Department of Biology, University of Antwerp, Universiteitsplein 1, Antwerpen 2610, Belgium Institute of Tropical Aquaculture, Universiti Malaysia Terengganu, Kuala Terengganu, Terengganu 21030, Malaysia.
authors.forename: Hon Jung
authors.initials: HJ
authors.lastname: Liew
authors.affiliation: Department of Biology, University of Antwerp, Universiteitsplein 1, Antwerpen 2610, Belgium.
authors.forename: Gudrun
authors.initials: G
authors.lastname: De Boeck
authors.affiliation: Department of Biology, Ghent University, K.L. Ledeganckstraat 35, Gent 9000, Belgium.
authors.forename: Dominique
authors.initials: D
authors.lastname: Adriaens
authors.affiliation: Department of Biology, University of Antwerp, Universiteitsplein 1, Antwerpen 2610, Belgium Department of Movement and Sport Sciences, Ghent University, Watersportlaan 2, Gent 9000, Belgium.
authors.forename: Peter
authors.initials: P
authors.lastname: Aerts
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D001696:Biomechanical Phenomena; D023681:Cichlids / Q000502:physiology*; D005260:Female; D005880:Gills / Q000502:physiology; D006257:Head; D008297:Male; D008863:Microspheres; D009055:Mouth / Q000502:physiology*; D009068:Movement; D010063:Ovum / Q000502:physiology; D011187:Posture / Q000502:physiology; D012212:Rheology; D014741:Video Recording; D014867:Water / Q000502:physiology; D014965:X-Rays
chemical_list: D014867:Water
keywords: Biomechanics; Churning; Cichlids; Hydrodynamics; Jaw protrusion; Opercula; Tilapia; Ventilation