Head kidney, liver and skin histopathology and gene expression in gilthead seabream (Sparus aurata L.) exposed to highly polluted marine sediments from Portman Bay (Spain)

Biomarkers have become crucial tools in modern environmental assessment as they can help to predict magnitude of pollution. The head-kidney (HK) and liver (hematopoietic and xenobiotic metabolism organs, respectively) are the key organs in all fish toxicological studies, although the skin has received less attention in this respect. The impact of two different types of polluted sediment collected from Portman Bay (Spain) on HK, liver and skin gene expression in gilthead seabream (Sparus aurata L.) exposed for two weeks to the sediments was determined by real time-PCR. The expression levels of different antioxidant enzyme genes [superoxide dismutase (sod) glutathione reductase (gr) and catalase (cat)] and immune-related genes [interleukin -1β (il-1b), immunoglobulin M (igm), T-Cell receptor (tcr-b), cyclooxygenase-2 (cox-2), colony-stimulating factor 1-receptor (csf-1r) and hepcidin (hep)] was analysed. Expression varied depending on both the organ and gene studied: tcr-b, csf-1r and hep genes were down-regulated in HK, as were gr, tcr-b and il-1b in liver and gr and il-1b in skin, while cox-2 was up-regulated in skin after exposure to both sediments. Concomitantly, histopathological alterations were also studied in HK, liver and skin. While no significant changes were detected in skin cells of fish reared in aquaria with polluted sediments marked changes in the general morphology of HK and liver were observed, accompanied by a substantial degree of cell death and melano-macrophage centre disorganization. The present study suggests that the biomarkers studied in gilthead seabream could be useful for assessing the impact of pollution in coastal environments.