Physiological studies on the effect of copper nicotinate (Cu-N complex) on the fish, Clarias gariepinus, exposed to mercuric chloride.

Female catfish, Clarias gariepinus, were collected from the Nile River at Assiut region, were divided into 7 groups. The first group was left as control, and the second was treated with mercuric chloride (MC) for 3 weeks following by normal water for 1 week. The third, fourth and fifth groups were provided by MC (150 μg/ l of water). This treatment was continued for 3 weeks. Then, the fish were received CN instead of MC, for 1 week, with 15 and 25 mg CN/100 g wet food. The fifth fish group received diet supplemented with vit E (α-tocopherol) (100 mg/kg wet diet), for 1 week, instead of MC treatment. Vitamin E was used as standard antioxidant drug. Following 3 weeks of normal ambient water, the sixth and seventh aquaria received only CN for 1 week, with 15 and 25 mg CN respectively/100 g wet food, respectively. At the end of the experiment, Samples of liver, kidneys (posterior part), gills (right gills) and ovary were excised. The measurement included the oxidative stress parameters: carbonyl protein and total peroxide and the antioxidant enzyme activities superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST) in all selected organs. MC treatment induced harmful effect in fish, probably due to its enhancing effect on reactive oxygen species (ROS) production in fish organs especially the respiratory and osmoregulatory organs namely gills. The result suggests that this gill damage may exert hypoxic case, anoxia for different organs and some Cu excretion resulting in a magnification of ROS overproduction. Also, the observed oxidative stress in ovary tissue of MC-treated fish may affect fish fertility. The addition of CN in fish diets could protect the fish C. gariepinus against MC-induced oxidative damage showing recovery of fish organs. It could suggest that the detoxifying mechanism of action of CN is mainly due to its scavenging activity of free radicals rather than tissue healing.