Risk assessment and toxic effects of metal pollution in two cultured and wild fish species from highly degraded aquatic habitats.

Lake Qaroun is an inland lake at the lowest part of El-Fayoum depression, Egypt. It receives agricultural and domestic non-treated drainage waters, which are also used for aquaculture in Qaroun area. The results of the present study aimed to provide comparable data between wild (collected from Lake Qaroun) and cultured (collected from Qaroun fish farms and the reference site) Nile tilapia Oreochromis niloticus and mullet Mugil cephalus, as indicators of natural and anthropogenic impacts on aquatic ecosystem as well as to evaluate the human hazard index associated with fish consumption. Metal concentrations in fish tissues showed a species-specific bioaccumulation pattern. Statistically significant differences were observed in the mean metal concentrations with lower bioavailability in M. cephalus compared with O. niloticus in internal vital organs (liver, kidney, and muscle) but much higher in external organs (gill and skin). Histopathological alterations and evident damages were observed in gill, liver, and kidney of both species collected from Lake Qaroun and Qaroun fish farms compared with those from the reference site. The results showed significant increase of plasma aspartate aminotransferase and alanine aminotransferase activity as well as creatinine and uric acid concentration in both fish species from polluted locations. The human health hazard index showed that the cumulative risk greatly increases with increasing fish consumption rate, thus yielding an alarming concern for consumer health.

Genotoxic effects of metal pollution in two fish species, Oreochromis niloticus and Mugil cephalus, from highly degraded aquatic habitats.

In Egypt, Lake Qaroun and its neighbouring fish farms are in a serious environmental situation as a result of pollution by agricultural sewage and domestic non-treated discharges. The present study aims to evaluate genotoxic effects of toxic metals in cultured and wild Nile tilapia, Oreochromis niloticus and mullet, Mugil cephalus collected from these contaminated aquatic habitats, in comparison with fish from a non-polluted reference site. Heavy-metal concentrations (Cu(2+), Zn(2+), Pb(2+), Fe(2+) and Mn(2+)) in water and sediment samples were recorded. The condition factor (CF) was taken as a general biomarker of the health of the fish, and genotoxicity assays such as the micronucleus (MN) test and a DNA-fragmentation assay were carried out on the fish species studied. In addition to micronuclei, other nuclear abnormalities (NA) were assessed in fish erythrocytes. Degradation of the studied aquatic habitats revealed species-specific effects. A significant decrease in CF values associated with a significant elevation in MN and NA frequencies was observed in fish collected from the polluted areas compared with those from the reference site. Moreover, mixed smearing and laddering of DNA fragments in gills and liver samples of both fish species collected from the polluted areas indicate an intricate pollution condition. Results of the present study show the significance of integrating a set of biomarkers to identify the effects of anthropogenic pollution. High concentrations of heavy metals have a potential genotoxic effects, and genotoxicity is possibly related to agricultural and domestic activities.

Induction of cytochrome P450 1A1 as a biomarker of Benzo-a-pyrene pollution in Egyptian fresh water fish.

The activity of Ethoxyresorufin-o-dealkylase (EROD) in the liver of Oreochromis niloticus and Clarias gariepinus was evaluated as a response to experimental and natural contamination of water with Benzo-a-pyrene and/or cadmium. The activity was measured fluorimetrically in the hepatic S9 fraction while the content of the enzyme was measured by ELISA. The response appeared as early as six hours post exposure. This study also reveled that Oreochromis niloticus exhibits higher values of EROD activity than that of Clarias gariepinus. CYP450 1A1 content showed lower responsiveness when compared to EROD activity measurements. The present study also estimated the inhibitory effect of cadmium on CYP450 1A1 induction. The current results demonstrate that EROD activity reflects contamination of water with benzo-a-pyrene as a polycyclic aromatic hydrocarbon compound. Consequently it is a useful biomarker for monitoring this type of pollution.

The significance of cortisol for osmoregulation in carp (Cyprinus carpio) and tilapia (Sarotherodon mossambicus).

Changes in plasma cortisol and glucose concentration were studied in carp during acclimation from fresh water (FW) to 1.5% salt water and vice versa. There was an increase in cortisol and glucose concentration during acclimation from FW to salt water which lasted for several days. Reacclimation to FW did not cause clear changes in cortisol and glucose levels. One single injection of cortisol (0.2 mg/100 g or 1 mg/100 g) and additional transfer to salt water (1.5% for carp and 2.7% for tilapia) altered the changes caused by acclimation alone of cortisol, glucose, Na+ concentration, and the osmolality in plasma. Gill Na-K-ATPase activity was also influenced. The effects of cortisol on electrolyte concentrations during acclimation and on Na+-K+-ATPase activity differed in both types of fish. Cortisol clearly lowered the increase in plasma Na+ concentration of the stenohaline carp and increased the ATPase activity. The changes in plasma Na+ concentration of the euryhaline tilapia was not clearly altered and the enzyme activity was inhibited. The significance of these cortisol effects is discussed.