Response of Nile Tilapia,Oreochromis niloticus(L.) to Environmental Cadmium Toxicity During Organic Selenium Supplementation

This study was carried out to evaluate the resistance of Nile tilapia, Oreochromis niloticus (L.), fed on organic selenium (OS)supplemented diet to water-born cadmium (Cd) toxicity. Fish (14.8±1.3 g) were randomly distributed at a density of 10 fish in 100-L aquarium. Fish in three treatments were fed a diet (30% crude protein) containing 0.5 g OS/kg diet (T1 - T3), while three other treatments (T4 - T6) were fed a basic diet without OS. During the feeding trial, fish in all groups were then exposed to 0.0, 1.116, or 2.232 mg Cd 2+ /L for 6 weeks. The fish performance and all the biochemical aspects were affected significantly by both Cd concentration, Se supplementation, and their interaction. OS supplementation enhanced fish growth, survival, and feed utilization, meanwhile the exposure to Cd reduced them (T1 vs T4, T2 vs T5, and T3 vs T6). All fish body constituents except moisture content were significantly affected by OS supplementation, Cd level, and their interaction. Crude protein and total lipids in fish body decreased, while ash content and Cd residue increased significantly with increasing Cd levels. OS reduced significantly Cd residues in fish body. Moreover, OS supplementation reduced creatinine, uric acid, AST, and ALT to below those of Cd-exposed treatments. Serum lipids increased, while protein decreased only in Cd-exposed groups (T5 and T6). Glutathione peroxidase (GPX) activity increased significantly with increasing Cd level and it was higher in T1 vs T4, T2 vs T5, and T3 vs T6. It could be concluded that OS supplementation may reduce the harmful effect of waterborn Cd in fish, which in turn improves the growth, survival, and feed efficiency.