Hydrodynamic benefits of schooling as measured by tail beat and opercular frequency in killifish, Fundulus heteroclitus

by Kara Kinder Podkaminer

Tail beat frequency and opercular frequency of killifish, Fundulus heteroclitus, were used in this study to quantify the effect of position in schooling. The repeatedly seen formation in groups of swimming fish has led to the hypothesis of a hydrodynamic benifit to schooling. The hydrodynamic theory proposes that fish utilize the vortices shed from anterior fish to derive energy, thus reducing energy needed to swim at a given speed. However, the actual benefits have been difficult to verify. In order to measure energy, both opercular and tail beat frequencies were quantified at different positions within a school. The logarithm of opercular frequency significatly increased with swimming speed, as did tail beat frequency. Tail beat frequency significatly scaled with opercular frequency (p=0.0024), and was used as indicator of power because it appeared to be a more sensitive indicator of power changes due to position. For killifish, position was shown to significatly affect tail beat frequency (p=0.0044), with lowest tail beat frequencies at interior, offset positions though not directly posterior to another fish. This benefit was additive; the reduction in tail beat frequency was greater when the fish were positioned behind two anterior fish, in the interior of the school, as opposed to at the edge of the school, with a leader only to one side. The interior positions expend less energy to swim at the same speed as leading fish. These results imply that optimal positioning within a school allows fish to derive hydrodynamic benefits and lower energy usage in swimming.