الفهرس 
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Abstract
Tuna is an extremely important and high priced fish in the global market and plays a large role in the seafood trade, as well as, they are highly significant economic species. Tunas are Perciformes fishes of family Scombridae. They are highly migratory fishes that mainly distributed in tropical, subtropical and temperate oceans.
This investigation aims to assess the genotypes variation and molecular characterization among tuna fish that collected from certain Libyan and Egyptian coastal regions and their correlation to some of the ecological parameters such as temperature, hydrogen ion concentration (pH), salinity and dissolved oxygen (DO). Also, to study the genetic relationships among different tuna fish under investigation, on the molecular level using the most recent techniques ISSR and SRAP. In addition, to draw the consensus tree and calculate the similarity index among these different genotypes.
In the ISSR technique, nine primers were successfully amplified DNA fragments with a total number of 45. Out of these amplified fragments, 22 were polymorphic with ratio of 48.89%. The ISSR analysis proved that it is useful for characterization genotypes and assessment of genetic diversity among the genotypes of blue fin tuna. Also, proved that, as short as the distance between any two locations under investigation, the similarity increased between the two genotypes which collected from these two locations. On the other hand, the use of seven primers in SRAP technique were successfully amplified a total number of 59 fragments. Out of these 44 were polymorphic with ratio of 74.57%. The SRAP data analysis was useful for characterization genotypes and assessment of genetic diversity among the genotypes of blue fin tuna. The SRAP results reflected the fact that, as long as, the distance increased between the locations, the tuna genotypes became distantly related and vice versa.
The combined data of ISSR and SRAP were used to estimate the genetic similarity values among the six tuna genotypes, and proved that the highest similarity value among these six tuna genotypes (0.90) was recorded between Al-khums and Surt genotypes (the two most closely related genotypes). However, the lowest value (0.60) was recorded between (Egyptian and Sabratha genotypes) and (Egyptian and Al-khums genotypes) with the same similarity value (the two most distantly related genotypes). from the dendrogram it is possible to conclude that the similarity value increased as much as distances decreased between locations and vice versa. There are a negative relation between the similarity and the distance between these genotypes under investigation.
The current study showed that the presence of small tuna fish in Egypt more than in Libya is due to the appropriate temperature for the growth of small tuna and its interaction with the possible averages of other physico-chemical factors (pH, dissolved oxygen and salinity). This also explains that Libya and Egypt are more appropriate for tuna migration and reproduction, respectively. Even, the adaptive evolution at genomic loci may be associated with changes in such ecological factors.
The changes of the studied ecological parameters percentages could act as barriers which decrease the tuna fish migration and thus decreased the chances of mating between the different genotypes of different locations. However, this low chance of mating leads to the speciation that proved by means of the molecular investigation.