الفهرس 
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Abstract
:
The aim of this study was to investigate the genotoxic effects of polymetallic contamination with
Copper and Cadmium on Zebrafish Danio rerio and sludge worm Tubifex tubifex using environmentally
relevant doses of Cu and Cd found in Lake Manzala’s sediment. Zebrafish was exposed to contaminated
sediment with 315 mg Cu /kg and 85 mg Cd /kg for 7 days, in presence and absence of Tubifex worms.
Genotoxicity and metals bioaccumulation levels were measured in both fish and worm tissues. While the
responsible genes for metal detoxification and excretion were examined in zebrafish tissues (brain, gills,
muscles and digestive system). After 7 days of exposure, experimental conditions where fish were alone
recorded the highest turbidity values in water along with the highest values of total Cu and Cd
concentrations. The presence of Tubifex worms in the contaminated treatment caused elevation in TDS
value and dissolved Cd concentration in water. Among the 4 tested tissues, digestive system showed the
highest accumulation ratio for Cd followed by gills and muscles and the least concentration was in brain
samples. On the contrary, zebrafish brain showed the highest accumulation level of Cu. Also, significant
increase in Cu and Cd concentration in worm’s tissue was recorded. Zebrafish were more vulnerable to
DNA damage in presence of worms in the contaminated environment, as significant increase in relative
hybridization efficiency with OPB11 probe was recorded in that group. Though, significant decrease in
relative hybridization efficiencies was recorded in Tubifex worms in absence of Zebrafish. from gene
expression results, brain showed more response to the metallic contamination than in other tissues with
significant up-regulation in mt2, clock 1, laptm4α, Abcc1-1 and loc55682 genes, in absence of worms. And
Clock1 gene is recommended to be a competent biomarker gene, as it showed significant up-regulation in
all the tested tissues under the different experimental conditions.