| Dietary Pb, being one of the important Pb pollutants in aquaculture, could lead to toxic effects on aquatic animal and endangered the human health through food chains. In this study, the toxic effects of dietary Pb on tilapia (Oreochromis niloticus) were investigated, and the potential of using exposure effect index and toxicicty effect indexes to monitor dietary Pb contamination was evaluated. In addition, the experiment was carried out to investigate the effectiveness of layer silicate nanopartilce (LSN) on dietary Pb adsorption, and the effects of LSN on reducing dietary Pb toxicity was conducted on Pb residues in tissues and toxicity effect indexes. The main results were presented as follows:1 Effects of dietary Pb on Pb residues in tissues of tilapia and toxic effects of dietary Pb on tilapia480 fish (mean weight,32.17±0.34g) were selected and randomly divided into four treatments with six replicates (20 fish per replicate). After three weeks of acclimation, fish were fed with diet (0,100,400 and 800μg Pb/g dw diet) at 3-3.5% fresh body weight twice daily. At 15d,30d,45d and 60d of exposure period, fish were killed and weighted. Blood and tissue samples were collected and determined for corresponding indexes. The main results were shown as follows:It was indicated that Pb residues in tissues of tilapia increased with dietary Pb exposure concentrations and period. Moreover, Pb accumulated in sampled tissues in the following order:intestine> kidney> bone> stomach> liver> gill> spleen> testis> muscle> brain. The results showed that Pb residues in kidney and bone exhibited high Pb burden could be used as surrogate biomarkers to monitor Pb pollution, and Pb residues in intestine and stomach could indicate Pb contamination in diet specially.Pb concentration-dependent decreases in trace elements (Zn, Fe and Cu) content were observed in kidney, bone, liver, spleen and testis of tilapia. In different sampled tissues, trace elements (Zn, Fe and Cu) metabolisms were disturbed at various levers. It was showed that malonyldialdehyde (MDA) levels in liver and kidney increased with dietary Pb concentrations, total antioxidant capacity (T-AOC) and glutathione (GSH) levers in liver and kidney decreased with dietary Pb exposure concentrations. It was also demonstrated that glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) activities in liver and kidney were affected by dietary Pb in a dissimilar way:Pb concentration-related decreases in GSH-Px and SOD activities were observed in kidney, while these two enzyme activities in liver were stimulated in a Pb concentration-dependent manner. It was observed that tail length (TL), TDNA%, tail moment (TM) and olive tail moment (OTM) of peripheral blood cells in tilapia increased with the increasing dietary Pb concentrations. Alanine transaminase (ALT), aspartate transaminase (AST) and lactate dehydrogenase (LDH) activities in liver and kidney were affected by dietary Pb in a contrary way:Pb concentration-related decreases in ALT, AST and LDH activities were observed in kidney, while Pb concentration-dependent stimulative effects on above enzyme activities were observed in liver. It was also demonstrated that the inhibitory effects of dietary Pb on alkaline phosphatase (AP), Na, K-ATPase, Ca, Mg-ATPase activities in both liver and kidney were Pb concentration-dependent. The inhibitory effects of dietary Pb on amylase, trypsin and lipase enzyme activities were dietary Pb concentration-dependent. It was found that T3 and T4 levels in serum were inhibited in a Pb concentration-dependent manner. By observation of histological sections of liver, kidney and spleen in optical microscope, Pb concentration-related lesions could be detected in these tissues of Pb-exposed treatments. The results revealed that dietary Pb could lead to Pb concentration-dependent toxicity on tilapia, and cooperative above toxic effect indexes could indicate dietary Pb contamination.2 Effects of LSN on reducing dietary Pb toxicity240 fish (mean weight,32.24±0.38g) were selected and randomly divided into four treatments with three replicates (20 fish per replicate). The feeding experiment lasted for 60d after three weeks of acclimation. The treatments were denominated as follows: control treatment (basic dietary), LSN treatment (basic dietary added with 0.5% LSN), Pb treatment (basic dietary added with 100μg Pb/g dw), Pb+LSN treatment (basic dietary added with 100μg Pb/g dw and 0.5% LSN). After 60d of exposure period, fish were killed and weighted. Tissue samples were collected and determined for corresponding indexes. The main results were presented as follows:As compared with control treatment, supplementation of 0.5% LSN significantly reduced Pb residues in intestine, kidney, bone, stomach and spleen (P< 0.05). Compared to Pb treatment, Pb residues in intestine, kidney, bone, stomach, liver, gill, spleen, muscle, testis and brain of Pb+LSN treatment significantly decreased (P< 0.05), respectively. No significant differences on trace elements (Zn, Fe and Cu) content in kidney, bone, liver, spleen and testis were observed between control treatment and LSN treatment (P> 0.05). Compared to Pb treatment, trace elements (Zn, Fe and Cu) content in sampled tissues of Pb+LSN treatment increased insignificantly (P> 0.05). No significant differences on levels of MDA, GSH, T-AOC and activities of GSH-Px, SOD in kidney were observed between control treatment and LSN treatment (P> 0.05). Compared to Pb treatment, MDA level in Pb+LSN treatment decreased insignificantly (P> 0.05), while GSH level, GSH-Px activity and SOD activity were enhanced insignificantly (P> 0.05) and T-AOC level increased significantly(P< 0.05). No significant differences on TL, TDNA%, TM and OTM of peripheral blood cells were observed between control treatment and LSN treatment (P > 0.05). Significant decreases in TL, TDNA%, TM and OTM of peripheral blood cells of Pb+LSN treatment were observed when compared with that of Pb treatment. No significant differences on ALT, AST, AP, LDH, Na, K-ATPase, Ca, Mg-ATPase activities in kidney were observed between control treatment and LSN treatment (P>0.05). As compared with Pb treatment, ALT, AST, AP, LDH, Na, K-ATPase, Ca, Mg-ATPase activities in kidney of Pb+LSN treatment were insignificantly stimulated (P>0.05). No significant differences on amylase, trypsin and lipase activities in liver were observed between control treatment and LSN treatment (P>0.05). Compared to Pb treatment, amylase, trypsin and lipase activities in liver of Pb+LSN treatment increased insignificantly (P>0.05).In conclusion, LSN could reduce Pb residues in tissues and Pb toxicity through its effectiveness on Pb adsorption. |
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