Hi, Nadia

As far as I remember, 10% formaldehyde is a little too concentrated and can spoil the eggs. We used a 4% aqueous solution of formalin (about 20-30 ml for 5 g of faeces), and placed the samples in closed tubes for 48 hours in the refrigerator (4°C). This stops the development of the eggs. Subsequently storage at room temperature (25-30°C) can last for more than a month without significant change in egg count. (Aumont, G., N. Barre, S. Diaw, L. Ouattara, R. Pouillot, E. Tillard and G. Vassiliades (1995). Preservation of fecal samples and laboratory sources of variation in fecal strongyles egg counts of small ruminants from tropical regions. International Conference on Novel Approaches to the Control of Helminth Parasites of Livestock, Armidale (Australia). )

Regards