Growth performance and physiological response of African catfish, Clarias gariepinus (B.) fed organic selenium prior to the exposure to environmental copper toxicity

A growth trial was conducted to investigate the effect of organic selenium (OS) supplementation on the growth performance of African catfish, Clarias gariepinus (B.). After feeding trial, fish were exposed to environmental copper (Cu) toxicity for 7 days. Fish (68.7 ± 2.3 g) were randomly distributed at a rate of 400 fish into 16 tanks, 150 L each. Fish were fed a diet (30% crude protein) containing either 0.0 (control), 0.1, 0.3, or 0.5 g OS kg-1 diet for 12 weeks. The feeding rate was 3% of live body weight per day. The amount of feed for each tank was divided to 2 equal meals and offered to fish at 9:00 and 14:00 h; 5 days a week. After feeding trial, a part of fish per each treatment were randomly used to determine the lethal concentration of Cu after 96 h exposure (96-h LC50). The rest of fish were further exposed to sublethal Cu dose (2.27 mg Cu2+ L-1) for 7 days. Growth performance and feed efficiency of fish fed on 0.3 g OS kg-1 diet were significantly (P < 0.05) higher than fish in other treatments. No significant difference in fish survival was observed due to OS supplementation. The highest values of red blood cells (RBCs) count, hemoglobin (Hb), hematocrit (Ht), glucose, total lipids, or uric acid were obtained when fish were fed on 0.3 or 0.5 g OS kg-1 without significant difference between them. Moreover, fish fed on 0.5 g OS kg-1 exhibited the highest values of total protein, albumin, globulin, aspartate amninotransferase (AST), alanine aminotransferase (ALT), or glutathione peroxidase (GPX) (P < 0.05), while fish fed on control diet exhibited the lowest values. Fish fed on 0.3 g OS kg-1 exhibited higher 96-h LC50 value than fish fed on the other diets. All parameters of fish fed 0.3 g OS kg-1 and further exposed to environmental Cu were near to those of negative control group. Fish fed non-OS supplemented diet and exposed to Cu (positive control) exhibited the highest values of physiological parameters. The data of the present study recommend to add 0.3 g OS per kg diet to improve fish growth, fed utilization and their vitality against environmental copper toxicity.