EFFECTS OF CHRONIC COPPER EXPOSURE ON THE MACROPHAGE CHEMILUMINESCENT RESPONSE AND GILL HISTOLOGY IN GOLDFISH (CARASSIUS-AURATUS L)

The effects of chronic copper exposure on the macrophage chemiluminescent response and gill histology in goldfish (Carassius auratus L.) were determined. Fish were exposed to sublethal concentrations (30, 65, 100, and 175 ppb) of copper sulphate for 96 h. Pronephric (head kidney) cells were collected and were comprised on lymphocytes, thrombocytes, monocytes/macrophages neutrophils and eosinophils/basophils (cell types grouped due to difficulty in identification). There were no significant differences in population profiles of cells used for chemiluminescence studies after exposure to 100 ppb copper. Density gradient-separated cells were stimulated with zymosan, the luminol-enhanced chemiluminescence (CL) response was measured and the results were compared to non-copper exposed controls. There was a significant correlation between copper concentration and reduction in the time at which the peak CL response [time to peak (TTP) CL] occurred. In addition, there was a significant parabolic dose response curve for peak CL response, which suggests increased production of reactive oxygen intermediates by phagocytes from fish exposed to concentrations up to 100 ppb, followed by inhibition at 175 ppb. These results indicate that copper affects phagocyte function in a complex manner, stimulating or inhibiting production of reactive oxygen intermediates depending on copper concentration. Exposure to concentrations of copper also resulted in varying degrees of gill hyperplasia. The relative median severity score (a score assigned to each gill based upon the amount of hyperplasia seen in a histological section) correlated significantly with the copper concentration. In addition, there was a very high correlation between the degree of hyperplasia and the TTP CL response. Levels of copper in the head kidney of goldfish exposed to 100 ppb were similar to controls as measured by atomic absorption spectroscopy. Thus, changes in the CL response of head kidney phagocytes of fish exposed to copper may be caused indirectly, via effects on other immunoregulatory cells or other physiological mechanisms. We conclude that addition of heavy metals such as copper to water can modify the CL responses of phagocytes and alter the histopathology of the gills in C. auratus.