Modulation of superoxide production in goldfish (Carassius auratus) exposed to and recovering from sublethal copper levels

Abstract

The effects of copper and recovery from sublethal (100μg/l) copper exposure were studied in three groups of goldfish (Carassius auratus) (1) control (2) copper (4–25d) and (3) recovery (4d exposure followed by 3–21d recovery). The mean concentration of copper measured in the liver of the continuously exposed group was significantly higher than in the control and recovery groups by 11 and 18 days of exposure, respectively. In the posterior kidney, copper accumulation in the copper group was not significantly greater than the control and recovery groups until 18 days of exposure. The liver contained 4–5-fold higher concentrations of copper than the posterior kidney in all three treatment groups. Levels of copper in the posterior kidney correlated with those of the anterior kidney. There were no measurable differences in liver, kidney, or serum copper levels within or between the control and recovery groups at any time point. The production of superoxide (O2−) was compared between groups by measuring the reduction of NBT in anterior kidney phagocytes. In the copper group, production of O2−increased compared to controls in response to exposure periods lasting up to 11 days. O2−production in the recovery group also increased in response to 4 days of copper exposure. However, after 3 and 7 days of recovery, O2−production decreased below then increased above the control levels, respectively. By 18 days of copper exposure or 14 days of recovery, O2−production was no longer significantly different from control values. To determine if the decreased O2−production measured on recovery day 3 was mediated by a humoral factor, phagocytes from untreated fish were incubated with serum from control or 3d recovery fish. Compared to the control serum,in vitroexposure to serum from copper-recovered animals resulted in a 29–34% decrease in O2−production. This was consistent with the 25% decrease measured in phagocytes from copper-recovered animals. It is concluded that the decrease in O2−production demonstrated in goldfish recovering 3 days from acute (4d) sublethal copper exposure is not due to a direct effect of copper but to a factor(s) present in the serum of the recovering animals.