title: The hydrodynamic trails of Lepomis gibbosus (Centrarchidae), Colomesus psittacus (Tetraodontidae) and Thysochromis ansorgii (Cichlidae) investigated with scanning particle image velocimetry.
abstract: The hydrodynamic trails of fish belonging to the families Centrarchidae, Tetraodontidae and Cichlidae were investigated. Water movements were measured in six horizontal planes, spaced 10-12 mm apart, for up to 5 min after the passage of a fish, using a computer controlled array of modulated laser diodes. We measured continuously and non-continuously swimming fish. Water velocities decayed rapidly in the leading seconds after the passage of a fish, but could still be measured for a period considerably longer than that. In still water (median water velocity <0.5 mm s(-1)), the hydrodynamic trails of Lepomis gibbosus lasted for more than 5 min. The trails of Colomesus psittacus and Thysochromis ansorgii could be detected for more than 30 s and more than 3 min, respectively. The water disturbance left behind by these fish was sufficient to be sensed by a piscivorous predator at a distance where vision or hearing frequently fail. Acoustic stimuli estimated from a dipole model in a distance that would be covered by the tested fish in 1 min (4-25 m) were 1.5 x 10(-7) to 3.1 x 10(-10) m s(-2), while the hearing threshold of a perch is three orders of magnitude above that. By contrast, the fish wakes after 1 min (except for one Colomesus wake) contained water velocities between 0.95 and 2.05 mm s(-1), which are within the detection range of hydrodynamic sensory systems. The three species differed with respect to water velocities, the spatial extent of the fish-generated water disturbances and the structure of the wake.
authors.affiliation: Institut für Zoologie der Rheinischen Friedrich-Wilhelms-Universität Bonn, Poppelsdorfer Schloszligbeta;, D-53115 Bonn, Germany. hanke@neurobiologie.ruhr-uni-bochum.de
authors.forename: Wolf
authors.initials: W
authors.lastname: Hanke
authors.forename: Horst
authors.initials: H
authors.lastname: Bleckmann
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D005399:Fishes / Q000502:physiology*; D013045:Species Specificity; D013550:Swimming / Q000502:physiology*; D014741:Video Recording; D014872:Water Movements