Figure 2.
Different species of fish use different modes of swimming, ranging from a nearly constant speed to bouts and pauses in motion. (a) Time evolution of individual speeds |vi| for 1 ≤ i ≤ N in a school of Paracheirodon Innesi. Each speed is displayed with a vertical shift in order to show the activity of each fish in the school. Speed scale is given in the upper left corner. Most of the time, fish have a nearly zero speed before suddenly exhibiting high accelerations followed by a speed decrease (legend from (C. Becco & N. Vandewalle 2009, Experimental study of collective behaviours in fish swarms, unpublished data)). (b) Time series of the speed of an individual in a group of four Kuhlia mugil. (c) The cumulative sum yields a linear relationship over the experiment's duration, opening the way for a constant speed modelling.