Meeting Abstract

80.4  Monday, Jan. 6 11:00  The effects of viscosity on swimming in lampreys (Petromyzon marinus) TYTELL, E. D.*; OSWALD, L. E.; Tufts Univ.; Tufts Univ. eric.tytell@tufts.edu

For most animals, locomotor movements result from a coupling between a flexible body and external environmental forces. To better understand this coupling, it is helpful to alter the balance of internal and external forces. Therefore, we examined the steady swimming kinematics of lampreys swimming in normal water, and water in which the viscosity was increased by 10 and 20 times by adding methylcellulose. Increasing the viscosity over this range increases the drag coefficient, potentially increasing fluid forces up to 40%. Previous computational results suggested that if lampreys did not compensate for these forces, the swimming speed would drop by at least 50% and body wavelength would decrease by about 25%, while tail beat frequency would remain the same. Five juvenile sea lampreys (Petromyzon marinus) were filmed swimming through still water and midlines were digitized using standard techniques. Swimming speed was about 1.77 body lengths (L) / s in normal water, and dropped by 40% in 10x viscosity, and by a further 51% in 20x viscosity, corresponding to Reynolds numbers of 1300, 80, and 20, respectively. Tail beat frequency also decreased: from about 3Hz in normal water to 2.9Hz and 2.3Hz in 10x and 20x viscosity, respectively. Body wavelength, contrary to our expectation, remained fairly consistent at 0.68 L. The estimated drag coefficient, using a cylindrical approximation, increased as expected in higher viscosity. Due to the large drop in speed, however, the estimated drag forces still decreased as viscosity increased. Thus, lampreys do change their muscle activity in high viscosity water, but perhaps not in response to higher drag forces. Future work may need to examine the changing dynamics of vortex shedding at the range of Reynolds numbers to account for the change in swimming speed.