2.2. Electron microscopy observations Sodium phosphotungstate (2%) was employed as a negative stain.
10 l of the hemolymph (from diseased E. sinensis) fixed with 2.5% glutaraldehyde was collected on formvar-coated copper grids for 1 min.
The wet residues were immediately covered with the stain for 30 s, which was then withdrawn by filter paper.
The grid was air dried before examination using a transmission electron microscope .