The swimming behaviour of microorganisms can be strongly influenced by the
rheology of their fluid environment. In this manuscript, we experimentally
investigate the effects of shear-thinning viscosity on the swimming behaviour
of an undulatory swimmer, the nematode Caenorhabditis elegans. Tracking methods
are used to measure the swimmer's kinematic data (including propulsion speed)
and velocity fields. We find that shear-thinning viscosity modifies the
velocity fields produced by the swimming nematode but does not modify the
nematode's speed and beating kinematics. Velocimetry data show significant
enhancement in local vorticity and circulation and an increase in fluid
velocity near the nematode's tail compared to Newtonian fluids of similar
effective viscosity. These findings are compared to recent theoretical and
numerical results
