Dietary EDTA supplementation improved growth performance, biochemical variables, antioxidant response, and resistance of Nile tilapia, Oreochromis niloticus (L.) to environmental heavy metals exposure

Feed supplements are generally used to improve fish growth, health, and immunity but their potential use to enhance fish resistance against environmental stress is limited. An eight-week feeding trial was conducted to determine the effect of sodium salt of ethylene diamine tetraacetic acid (EDTA) supplementation on growth performance, biochemical and antioxidants response, body composition, and resistance of Nile tilapia, Oreochromis niloticus (L.) to environmental heavy metals (HM) exposure. Fish (16.2 ± 0.28 g) were fed on diets enriched with 0.0, 5, 10, 15, and 20 g EDTA/kg diet. After that, fish were exposed to synthetic mixture of lead (Pb), cadmium (Cd), copper (Cu), and zinc (Zn) concentrations similar to those in the natural polluted habitat for 7 days. Fish performance and feed intake improved significantly with increasing EDTA levels up to 10 g/kg diet after which fish growth declined. All biochemical variables are significantly affected by EDTA supplementation, HM exposure, and their interaction. In response to EDTA supplementation, antioxidant activities were improved due to EDTA supplementation especially when fish fed 10-20 g EDTA/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 EDTA/kg diet was significantly improved and it was near that of fish prior HM exposure. Regarding whole-fish body constituents, only crude protein content was significantly higher in EDTA-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 EDTA supplementation reduced HM concentrations in whole-fish body and subsequently reduced their impacts on biochemical and antioxidant activities especially in fish fed 10-20 g EDTA/kg diet. The polynomial regression data of this experiment recommended the use of EDTA supplement at level of 13 g/kg diet to improve fish performance and antioxidant activity.