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Chromium is widely used in industrial processes, and is released into aquatic environments by electroplating, tannery and textile industries. Fishes in natural waters or in aquaculture facilities supplied with these waters are exposed to chromium waste and are presumed to be affected by deposits. Herein, we examine the effect of hexavalent chromium on carp Cyprinus carpio derived immune cells. In vitro exposure of carp leukocytes to hexavalent chromium induced cytotoxicity, decreased mitogen-induced lymphocyte activation and phagocyte functions at concentrations between 2 and 200 micromol Cr l(-1). Neutrophils responded to chromium challenge by changes in cell shape together with reduced nitric oxide and reactive oxygen production. This occurred at much lower concentrations than for the cytotoxic effects seen in leukocyte cultures derived from peripheral blood or pronephros. In a similar way, activation of carp lymphocytes by pokeweed mitogen was reduced in a dose-dependent manner, while cytotoxic effects on non-activated lymphocytes were observed at much higher doses of 200 micromol Cr l(-1). Altered lymphocyte and neutrophil functions are considered to be responsible for decreased resistance to pathogens observed in fishes under chronic chromium challenge.

A flow cytometry protocol was applied for the detection of neoplasia in Macoma balthica L. from the Gulf of Gdansk (Baltic Sea, Poland). A simple method, based on an osmotic shock, was used to permeabilise gill cells. The cytometric pattern of normal clams consisted of 2 peaks, a major peak B and a smaller peak C. The cytometric pattern of affected clams consisted of 2 peaks named B' and C'. Two parameters were used to define the stages of abnormalities in M. balthica clams based on the percentage of cells in peaks B, C, B' and C' and on the ratio between the fluorescence value of peaks B, C, B' and C' in all individuals. Three stages of neoplasia were clearly distinguished by flow cytometry considering peak C'. Stage 1 was characterised by a major population of cells in peak B' and more than 10 % of cells in the C' peak. Stage 2 consisted of a lower percentage of cells in peak B' and more than 25 % of cells in peak C'. Stage 3 of the neoplasia was characterised by a further reduction in peak B' and more than 40 % of cells in peak C'. Flow cytometry allowed for objective detection of neoplasia and provided a rapid method for measuring the DNA content of thousands of cells per individual. The accuracy of flow cytometry was assessed by comparing with standard histological techniques, used here as a reference technique for the detection of neoplasia, and with chromosome analysis. All individuals were analysed in parallel using the 3 techniques. The proportion of normal and affected individuals diagnosed using flow cytometry was comparable to the proportion determined by histology and chromosome analysis.