Effects of commonly used fixatives on size parameters of freshwater planktonic protists
Chaput, Olivier; Carrias, Jean-François
published: Apr 10, 2002
ArtNo. ESP141015503009, Price: 29.00 €
We tested the effect of four commonly used fixatives (Lugol's iodine, mercuric chloride, glutaraldehyde and formaldehyde) on cell length, width and volume of six species of freshwater planktonic protists. Most of the fixatives significantly influenced the cell dimensions of these species. Significant changes in the volume of protists, expressed as a percent of the average live cell volume, ranged from -64 to +59 %. Changes in cell volume were highest for heterotrophic flagellates and scuticociliates, indicating that the biomass of these protists in freshwater systems has probably been underestimated in experiments in which volume estimates were based on fixed samples. The effects were, in the order of increasing change in cell parameters: formaldehyde < glutaraldehyde < Lugol's iodine < mercuric chloride. We observed differences between taxa in their response to the same treatment, particularly for the mercuric chloride fixation. In addition, opposite responses were noted for the scuticociliate species. In the light of our study and other works, we recommend the application of conversion factors of 1.4 and 1.7 for Lugol's and glutaraldehyde-fixed cells, respectively, to accurately estimate the biovolume of protists in fixed samples.