Exposure to waterborne copper reveals differences in oxidative stress response in three freshwater fish species

Among species, various strategies in metal handling can occur. Moreover, the same metal concentration, or even the same metal dose, does not always seem to exert the same effect in different species. Here, we have investigated differences in a copper induced oxidative stress response between rainbow trout (Oncorhynchus mykiss), common carp (Cyprinus carpio) and gibel carp (Carassius auratus gibelio). Fish were exposed to two sub-lethal Cu concentrations, an identical concentration of 50 μg/l for all fish species and an identical toxic dose which was 10% of the concentration lethal to 50% of the fish within 96 h of exposure (LC50 96 h value) for each of the 3 species (20 μg/l for rainbow trout, 65 μg/l for carp and 150 μg/l for gibel carp). Different anti-oxidative enzyme (superoxide dismutase, glutathione reductase and catalase) activities and anti-oxidant (reduced glutathione and reduced ascorbate) concentrations were determined in gill samples collected after 1 h, 12 h, 24 h, 3 days, 1 week and 1 month of Cu exposure. Changes in the measured parameters were present in all 3 species, yet a clear differentiation between fish species could be made before and during the exposure. The ascorbate levels of gibel carp were twice as high as those in common carp or rainbow trout. In contrast, the level of glutathione in rainbow trout was more than twice of that in the two other species. Also, glutathione reductase activity of rainbow trout was higher than in the other species. In rainbow trout a decrease of reduced ascorbate and reduced glutathione was observed in the beginning of the exposure, indicating that ROS scavenging molecules were under pressure. This was followed by an increase in the activity of superoxide dismutase after 3 days of exposure. In contrast, common carp and especially gibel carp enhanced their anti-oxidant enzyme activities as quickly as in the first day of exposure. Furthermore, our research seems to confirm that some fish rely more on glutathione as a first line of defence against metal exposure, while others rely more on metallothionein in combination with anti-oxidant enzymes.