الفهرس 
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Abstract
This study was carried out at Genetics Department laboratories, Faculty of Agriculture, Kafrelsheikh University.
This study aimed to estimate the genetic diversity within and among populations of three Tilapia species e.g., Oreochromis niloticus, Tilapia zilli and Oreochromis aurea which were collected from three locations. Two of these locations were from Kafr El-Sheikh Governorate, i.e., Ryad (locates at Middle of Kafrelsheikh Governorate) and Motobs (which located at North-West of Kafrelsheikh Governorate and adjacent to Mediterranean Sea, Al-Borolos lake and Nile River). The third one was from Bahr El Baqar at El Sharqia Governorate. Ten individuals from each population were used except Bahr El Baqar population of O. aurea since five individuals were used according to sampling limitation. This study was conducted using molecular and biochemical studies. The obtained results indicated the following:
a- Molecular studies:
a-1- Random amplified polymorphic DNA (RAPD):
Five randomly primers were used with each of the three genotypes which were collected from three different locations. The obtained results indicated that the percentages of polymorphism in populations of O. niloticus were 61.42, 63.63 and 47.27%, in populations of T. zilli were 44.44, 44.59 and 35.08 % and in populations of O. aurea were 46.15, 20.68 and 25.86 % with Ryad, Bahr El-Baqar and Motobs, respectively.
a-2- Sequences related amplified polymorphism (SRAP):
The highest three polymorphic individuals from each location for each species were selected to be applicated with SRAP technique to confirm the polymorphism statues from RAPD application.
Summary
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With comparing the polymorphism percentages which obtained from RAPD and SRAP application respectively, it was found that the highest percentage of polymorphism was detected in O. niloticus (58.41 and 68.96) followed by T. zilli (41.87 and 33.33) and O. aurea (31.49 and 17.64) out from application of RAPD and SRAP, respectively. There was no constant trend of similarity could be detected between or among the selected individuals when SRAP technique was adopted.
a-3- Phylogenetic analysis:
Population from Ryad was closer to population of Bahr El Baqar in O. niloticus, while populations of T. zilli and O. aurea from Bahr El Baqar were more similar to population from Motobs according to RAPD.
b- Biochemical studies:
Total soluble protein and esterases isozymes were extracted from flesh (muscles) and liver of all individuals from the three species under study to estimate the genetic diversity of the selected populations.
b-1- Flesh total protein:
With comparing the obtained bands from the three O. niloticus populations which were collected from three different locations, it was found that 13 bands out of the 20 were common bands among the three populations. Moreover, two bands were common between Ryad and Bahr El-Baqar. Finally, other two bands exhibited special relation between Bahr El-Baqar and Motobs. Exacting appearance of one band in Bahr El-Baqar and completely absence in Ryad and Motobs locations.
The three T. zilli populations which were collected from three different locations exhibited 8 bands out of the 21 were common bands among the three populations. Moreover, two bands were common bands between Ryad and Bahr El-Baqar. One band exhibited special relation between Ryad and Motobs. Four bands appeared in Bahr El-Baqar and
Summary
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Motobs. Exacting appearance, six bands in Ryad and completely absence in Bahr El-Baqar and Motobs locations.
The three O. aurea populations exhibited 10 bands were common between three populations, while the rest of bands appeared in some of population and disappeared in the other. Moreover three bands were common between Ryad and Bahr El-Baqar population. Three bands appeared in populations Bahr El-Baqar and Motob. Four bands presented as specific in Motobs population and three bands were specific for Ryad population.
b-2- Liver esterases
Detection of non-specific esterase isozymes (α & β esterases) from liver extracts was studied in order to use it as differential biochemical marker within and among the three different Tilapia species under study.
Ryad and Motobs individuals of O. niloticus showed four isozymes. Meanwhile, Bahr El-Baqar exhibited only three. Ryad and Bahr El-Baqar individuals of T. zilli showed three isozymes. Meanwhile, Motobs exhibited four ones. The majority of individuals within or among the three locations varied in esterases isozymes activities. Maximum two isozymes were detected in population of O. aurea. Band 1 was dark in Ryad individuals and ranged from very faint, faint and dark in Bahr El-Baqar and Motobs. Band two was very dark in three populations except sample no 2 in Bahr El-Baqar population.
Present study concluded also that the very high similarity within each population individuals leads to high probability of mating between individuals, but not among them. These findings are an indication for the distinct among populations from different regions and these inbreed populations.