The swimming velocity of the cells was
strongly impaired by the detergent. The NOEC and EC50 values obtained
for velocity were much lower than those for motility, i.e. the
velocity of the cells was found to be more sensitive than the %
motility. This can be explained by the fact that the detergent lowered
the speed of the cells but the cells were still swimming
(though at lower speed than in the control) and hence counted
as motile which resulted in smaller inhibition of %motility as compared
to velocity. These results are in agreement with previous
studies reporting the higher sensitivity of velocity than motility
in E. gracilis to different substances like heavy metals,