الفهرس 
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Abstract
This study provides an updated information on the length weight relationships and condition factors of two species chrysichthys auratus and chrysichthys rueppelli, in six khors from Lake Nasser (Toshka, Hamedo, Garf Hussein, Amada, Gazal and Sheniara), Egypt. It also investigates how these parameters are affected by variation in environmental characteristics of the Lake; therefore, it presents the first reference of genetic diversity of chrysichthys auratus and chrysichthys rueppelli data in Lake Nasser. The results showed that the total length of chrysichthys auratus in khor (Gazal) was significant comparable with the other khors, but it was non significant among (Sheniara, Amada and Garf Hussein), also it was non significant between (Toshka and Hamedo), but between the other was significant, the total weight was significant in the following khors (Gazal, Garf Hussein and Amada), and non-significant between the other khors (Toshka, Sheniara and Hamedo). The relevant length-weight correlations for chrysichthys auratus and chrysichthys rueppelli exhibit a growth mode that is negative allometric. The chrysichthys auratus and chrysichthys rueppelli condition factors show that the fish are healthy and live in good condition, it was 1.4 for chrysichthys auratus and1.15 for chrysichthys rueppelli. For chrysichthys auratus and chrysichthys rueppelli, the overall sex ratio showed a higher proportion of females than males; the ratios of males to females were1:3 and 1:1.3respectively for all khors. The present study discovered a full mitochondrial barcode identity between the morphologically described species, chrysichthys rueppelli and chrysichthys auratus. IV This sample of chrysichthys auratus’s mitochondrial genotype was the same as those previously collected from various locations along the Nile in Egypt and other East African nations. It had a low level of mitochondrial genetic barcode identification, although it shared a monophyletic relationship with the West African chrysichthys auratus. Compared to a few other Nile fish, chrysichthys auratus in Lake Nasser displayed a higher level of genetic variety, which may indicate that the species is doing well in that environment. The current study suggests conducting additional research to determine the causes that go beyond the profound morphological variations between the two specimens that were determined to be chrysichthys auratus and chrysighthys rueppelli. In order to distinguish between chrysichthys auratus and chrysichthys rueppelli, just one molecular investigation using isoelectric focusing of eye lens and other external characteristics, primarily those of chrysichthys rueppelli—which has larger standard length, a relatively shorter first dorsal fan ray, a wider head, longer upper and lower jaw lengths, a longer caudal peduncle, longer pectoral and parapelvic fins, and smaller eyes than those of chrysichthys auratus were noted in other studies, though. These results, however, did not support our findings that both forms belong to the same species, as confirmed by DNA barcode identity among all samples gathered and examined in the current study.