Chromosomes of 6 bivalve species were studied from mitotic metaphases using cell suspension techniques. Among Family Mytilidae, Modiolus barbatus (Linnaeus 1758) has a diploid chromosome number of 2nϭ32 with 5 metacentric, 2 submetacentric, 5 subtelocentric and 4 telocentric chromosome pairs, Septifer excisus (Wiegmann 1837) has 2nϭ26 with 9 metacentric, 2 submetacentric, and 2 telocentric chromosome pairs and Septifer bilocularis (Linnaeus 1758) also has 2nϭ26 with 8 metacentric, 2 submetacentric and 3 subtelocentric chromosome pairs. Among Family Veneridae, Ruditapes decussatus (Linnaeus 1758) has 2nϭ38 with 6 metacentric, 5 submetacentric, 3 subtelocentric and 5 telocentric chromosome pairs, Circe scripta (Linnaeus 1758) has 2nϭ38 with 6 metacentric, 6 submetacentric, 4 subtelocentric and 3 telocentric chromosome pairs and Venus verrucosa (Linnaeus 1758) has also 2nϭ38 with 7 metacentric, 4 submetacentric, 4 subtelocentric and 4 telocentric chromosome pairs. These results are reported for the first time in Egypt.

Chromosomal analysis of the three Egyptian species, Unio elongatulus (Family: Unionidae), Mutela rostrata (Family: Mutlelidae) and Corbicula fluminalis (Family: Corbiculidae) have been studied. The diploid chromosome number of these three species are 2n=28, 2n=20 and 2n=26 respectively.Comparative analysis of the karyotypic data of these three species had been discussed. To the best of the author knowledge, these results are reported for the first time in Egypt.

Genetic variability among three species of red sea fishes (Lethrinus borbonicus, Siganus rivulatus and Mulloidichthys flavolineatus) were determined to evaluate the effect of petroleum oil component pollutions on the fishes using Inter-simple sequence repeats (ISSRs) and sodium dodecyl sulfate-polyacrlamide gel electrophoresis (SDS-PAGE) markers. According to ISSR analysis of DNA, nineteen (19) ISSR primers generated a total of 465 bands with an average 24.5 bands per primer. Analyses of SDS-PAGE protein, 137 bands were identified variant bands from 44, 43 and 50 in sample Lethrinus borbonicus, Siganus rivulatus and Mulloidichthys flavolineatus respectively. Analysis of SDS-PAGE protein provided more precise information concerning of the effect of petroleum oil components on protein subunits and genetic variation in Siganus rivulatus species than ISSR-PCR of DNA. Whereas ISSR technique showed more polymorphism or relatively a close to the percentage of SDS-PAGE result among the tow species Lethrinus borbonicus and Mulloidichthys flavolineatus compared to there controls. A remarkable result from this study was identifying that petroleum oil components pollution have distinct effect in genetic structure of fishes and lead to disappear of some protein subunits or appear new some protein subunits in fish muscle tissues.

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