Effect of dietary active charcoal supplementation on growth performance, biochemical and antioxidant responses, and resistance of Nile tilapia, Oreochromis niloticus (L.) to environmental heavy metals exposure

Environmental pollution adversely affects fish growth and health. Thus, the search for agents having protective role against pollutants toxicity with potential natural biological occurrence is worthwhile. An eight-week feeding trial was conducted to determine the effect of dietary active charcoal (AC) supplementation on growth performance, biochemical and antioxidants responses, body composition, and resistance of Nile tilapia, Oreochromis niloticus (L.) to environmental heavy metals (HM) exposure. Fish (14.6 +/- 0.54 g) were fed on diets enriched with 0.0, 2, 5, 10, and 20 g AC/kg diet. After that, fish were exposed to synthetic mixture of lead (Pb), cadmium (Cd), copper (Cu), and zinc (Zn) concentrations similar to those of the natural aquatic habitat for 7 days. The unionized ammonia was adversely affected by dietary AC levels where lowest ammonia concentration was observed at 20 g AC/kg diet and its highest concentration was obtained at the control group. Fish performance and feed intake improved significantly with increasing AC levels up to 10 g/kg diet after which fish growth declined. All biochemical and antioxidant variables are significantly affected by AC supplementation, HM exposure, and their interaction. In response to AC supplementation, antioxidant activity was significantly improved especially when fish fed 10-20 g AC/kg diet. Post HM exposure, the control fish exhibited highest superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities and lowest malondialdehyde (MDA) value, meanwhile antioxidant activity of fish fed 10-20 g AC/kg diet was near that of fish prior HM exposure. Additionally, no significant differences were observed in whole-fish body constituents but only crude protein content was significantly higher in AC-fed fish than the control fish. After HM exposure, total ash contents and HM residues were significantly higher but crude protein and total lipids contents were significantly lower than those of the control fish. It is also noticed that AC supplementation reduced HM concentration in fish body and subsequently their impacts on biochemical and antioxidant activities were significantly reduced especially in fish fed 10-20 g AC/kg diet. The overall data of this experiment showed that AC supplementation could improve fish performance, enhance the antioxidant activity and reduce the HM bioaccumulation in fish body and the optimum dietary AC level is 7.0 g/kg diet.