Meeting Abstract
7.1 Thursday, Jan. 3 Hydrodynamics of schooling in fishes HANKE, W.*; LAUDER, G. V.; Harvard; Harvard glauder@oeb.harvard.edu
The possibility that fish might gain an energetic advantage from hydrodynamic effects in a school has been discussed for more than thirty years, but has not yet been tested experimentally due to technical difficulties associated with recording details of flow experienced by fishes within the school. We used a scanning-PIV approach by designing a motorized rotating mirror drum with a staggered pattern of mirrors and a downstream mirror array, to generate a set of stationary horizontal light sheets that allow near-volumetric visualization of flow within a fish school. The rotating mirrors were synchronized with three megapixel high-speed video cameras which allowed tracking of the vortices produced by fish in front as these vortices pass fish in the back over many tail beat cycles within a volume of approximately 25*25*9 cm (length*width*height). This arrangement allows determination of the spatial and temporal relations between the vortex wakes produced by the fish in the front of the school, and the body kinematics of the fish in the back. Both 3D kinematic data and synchronized particle imaging views of small schools of fish (3 to 10 individuals) swimming in a flow tank at 0.5 to 6 body lengths per second were obtained. Based on experimental analyses of teleost species investigated so far (including giant danio, bluegill sunfish, golden shiner, silversides, cod, and smelt), we conclude that the hydrodynamic events in a school usually do not significantly influence the positioning and behaviour of the fish in the back of the school, and that hydrodynamic advantages appear unlikely to play a role in the formation of these schools. Using a self-propelling robot with two flapping foils, we simulate the flow in a two-dimensional school with two leading fish. We found indications that rainbow trout are able to use the combined wake of these synchronized flapping foils to reduce their swimming effort in a limited frequency range.
