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Pollution effects on haematological parameters in Pelophylax ridibundus individuals were investigated; animals were collected from two sites in Southern Bulgaria: the Tsalapitsa rice fields (RF) and the Vacha river (reference site, RS). Blood analysis showed significant differences between the haematological parameters of RBC, WBC, Hb, packed cell volume (PCV) and frogs' leucogram from RF and those from RS. These findings provide information on long-term background pollution of the habitat (RF) under investigation. In our view, the erythropenia, leucopenia, hypоchromia, lower values of PCV, St-neutrophilia, Sg-neutropenia, basopenia, eosinophilia, monocytosis and lymphopenia that were found in Pelophylax ridibundus individuals inhabiting the Tsalapitsa rice fields were probably caused by the pesticides and fertilizers that enter the paddy cages during the rice production process. The present study proves the practical usefulness of haematological parameters of Pelophylax ridibundus individuals in bioindication analyses for environmental assessment of agroecosystems.

The article presents the basic erythrocyte-metric parameters: cell length (EL) and width (EW), EL/EW, erythrocyte size (ES), nucleus length (NL) and width (NW), NL/NW, nucleus size (NS) and nucleocytoplasmic ratio (NS/ES) in the wild populations of marsh frogs Pelophylax ridibundus from five water bodies in Southern Bulgaria (two rivers and three reservoirs) with different degrees and types of anthropogenic pollution (less disrupted water basins, domestic sewage pollution and heavy metal pollution). The changes in erythrocyte-metric parameters depend on concentrations and types of toxicant and, to a lesser extent, on the type of water basin. We found that when P. ridibundus populations live in conditions of domestic sewage pollution, EL, EW and ES increase in comparison with the control samples, with regard to an elongated elliptical cell shape. Simultaneously, NL, NW and NS did not undergo any significant changes when compared with the control samples. The nuclei had elliptical shape. In the populations from the water basins with heavy metal pollution, EL, EW, ES, NL, NW and NS decreased. The cells and nuclei had a circular shape. NS/ES decreased when compared with the control sample, regardless of the type of toxicants.

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