Seasonal changes of basic erythrocyte-metric parameters in Pelophylaxridibundus (Amphibia: Ranidae) from anthropogenically polluted biotopes in Southern Bulgaria and their role as bioindicators.

The purpose of this research work is to present data that show the seasonal changes (spring-summer-autumn) of basic erythrocyte-metric parameters (ЕL: Erythrocyte length, ЕW: Erythrocyte width, ЕL/ЕW, ES: Erythrocyte size; NL: Nucleus length, NW: Nucleus width, NL/NW; NS: Nucleus size, NS/ES: Nucleus-cytoplasmic ratio) in Pelophylax ridibundus populations from three biotopes located on two rivers in Southern Bulgaria (less disrupted biotope, with domestic sewage pollution and heavy metal pollution). Differences of high statistical significance were found among the different populations. Within the population living in conditions of domestic sewage pollution, for the entire period of the investigation the erythrocytes and their nuclei had an elliptical shape (a slight elongation of ellipses in autumn) and the biggest sizes (EL, EW, ES, NL and NS were constantly higher than the less disrupted biotope), NS/ES, became significantly smaller in autumn. Throughout the period of investigation, the values of all nine cellular and nuclear parameters were statistically-significantly the lowest in the population from the biotope with heavy metal pollution. The parameters: EL, ЕW, NL, NW and ES became significantly lower, progressively and statistically, during seasonal transitions. Cells and nuclei grew ovular in shape in comparison to the populations from the other two biotopes (this process was most pronounced in autumn) and NS/ES numbers were significantly decreased in summer and autumn.