الفهرس 
MATERIAL AND METHODS
Studying the effect of pollution on the expression of aromatase genesOnly 14 pages are availabe for public view
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Abstract
The present study was carried out at El-Matariya research station for aquatic resources, Dakahlia Governorate, Egypt.
The objectives of this research were aiming to study the effects of some environmental stresses (salinity and pollution) on Nile tilapia (Oreochromis niloticus).
Studying the differential expression of the aromatases (CYP19a & b) in Nile tilapia tissues (ovary, testis and the brain of female) was the first goal and the topic of this research.
To win this goal, the impact of the surrounding environment should not be forgotten. Therefore, we studied the physicochemical characteristics of the surrounding environment beside the polyaromatic hydrocarbons and the organochlorine pesticides.
The histological study was very important to determine the possible effects of the environmental stressors on the gonads.
To accomplish the aims of this study, two separate experiments were designed as the following:
The first experiment was conducted to study the effects of different salinity levels (10‰, 15‰, 20‰, 25‰ and 30‰) as a stress on the expression of aromatase genes (CYP19a & b).
The second experiment was the study of the effects of pollution at Lake Manzala on the expression of aromatase genes
In conclusion, harmful substances like PAHs, heavy metals, and OCP are often released to Lake Manzala through industrial, agricultural, or sewage discharges. The aquatic environment has its specific impacts on surrounding fish populations. The sudden mortalities of fish may be resulting from the higher levels of pollutants discharged in waterways while the lower levels of these discharges may result in accumulation in aquatic organisms and consequently changing the gene pools of them.
The four studied locations recorded dangerous concentrations of PAHs that may cause great defects to aquatic organisms.
The examined total OCP at the studied sites of Lake Manzala, are clearly recorded the highest values of OCP at EL-Serw site.
The results of histological examination of gonads obviously showed that the stresses had their great effects on the gonads of O. niloticus.
The positive correlation was recorded between salinity levels and relative CYP19 expression in the gonads and the brain of females.
The relative expressions of CYP19a in ovaries and testes are directly correlated with the levels of pollution while the negative correlation was detected between the relative expression of CYP19b in brain of females and the levels of pollution.
The relative expressions of CYP19a in ovaries and testes are directly correlated with the levels of pollution while the negative correlation was detected between the relative expression of CYP19b in brain of females and the levels of pollution.