Meeting Abstract

P2.71  Monday, Jan. 5  Fish schooling: Measurements of Flow, School Structure, and Tail Beat Frequency HANKE, W.*; LAUDER, G.V.; Harvard University; Harvard University wolf.hanke@gmail.com

Fish can aggregate into groups known as shoals or, in the case of synchronized and polarized swimming behavior (Pitcher and Parrish, 1993), schools. More than half of the 30000 fish species known form schools at least at some point in their ontogeny. Our previous work has shown that hydrodynamic energy savings do not generally play a significant role in the formation of schools, contrary to the hydrodynamic hypothesis formulated by Weihs (Nature, 1973). However, a reduced tail beat frequency of the fish in the back of a school as compared to those in front has repeatedly been reported and has been interpreted as a sign of energy savings (Herskin and Steffensen, J. Fish. Biol. 1998; Svendsen et al., J. Fish. Biol. 2003). Here we present data from three species of fish (Devario aequipinnatus, Fundulus delineatus and Lepomis gibbosus) that do not show a reduced tail beat frequency of the fish in the back of a school. We suggest an explanation for the earlier, contradicting results based on wall and ground effects. Furthermore, we quantified the tail beat phase relations between individual fish in our schools and found that they were not fixed, as would be expected in case of a strong influence of the wake of a fish on a following conspecific. We confirm our conclusion that hydrodynamic effects have not been the driving force in the development of fish schooling. Furthermore we review the literature once more and raise some methodological concerns about experiments that have measured the actual endurance of single swimming fish versus groups.