Changes in fish macrophage aggregate centres (MACs) are a useful indicator of environmental stress. In this study we evaluated stereologically the values of these cells in the polluted sites compared to the clean site in the River Bregalnica. MACs aggregates were randomly distributed in spleen and often showed irregular form. Dominant pigment in them was hemosiderin. Relative volume of MACs aggregates showed significant higher value in brook barbel from polluted site. Total volume showed the same pattern, but differences were not significant. Our data confirm that increase in MACs aggregates may serve as to warn on potential pollution in aquatic ecosystems. However, the precaution is strongly suggested, as results were based on quantitative approach.

Macrophages are involved in innate and acquired immune responses, being key players in immunotoxicology. Changes in the quantities of pigmented macrophage aggregates (PMQ) in fish are often used as biomarkers of pollution. Most studies offer only qualitative data on PMQ changes, and effects of age, sex and season are poorly known. We present a stereological study of the relative and total volumes of PMQ in the barbel, Barbus peloponnesius spleen. Our focus is to disclose influences of age, sex and season on PMQ, and check if the there is any positive association with aging. The females had a significantly higher spleen and body weights and length. PMQ loaded with lipofuscin/ceroid and hemosiderin were dispersed throughout both spleen pulps. Seasons impacted on PMQ, despite no too markedly. Differences existed between sexes, with males having significantly higher relative volumes of PMQ: the total volumes had similar tendencies. The volumes of PMQ were positively associated with age. The new data reinforce the importance of studying influences of both intrinsic and extrinsic factors that model the quantities of PMQ so to better interpret their changes seen in biomonitoring works.