The aim of the study was to determine, whether the proteus (Proteus anguinus) blood cells from the archive collection provide a suitable material for estimation of nuclear genome size by image cytometry. Blood cells were sampled from the ventricle of the heart of archived animals and stained by Feulgen reaction with a Schiff reagent, which specifically stains DNA. Integrated optical density (IOD) was measured in red blood cell nuclei. The blood cells of archived specimens of common mudpuppy (Necturus maculosus) were used as standard, and blood smears prepared from fresh blood were used as control. The calculated C-values were highly variable and mostly differ from the known size of the proteus genome in the Animal Genome Size Database. Blood cells isolated from the hearts of animals from the archive were not suitable for IOD measurements and C-value calculations, since animals were mostly improperly fixed and archived. C-values comparable to published data were obtained on fresh blood smear samples and blood cells isolated from specimens fixed either in ethanol or formaldehyde and subsequently archived in ethanol. For further genome size studies with image cytometry, fresh blood smears are the most suitable. This also applies to common mudpuppy as standard.
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