الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 196 |  |  |
| | | from | 196 | | |
Abstract
Cooling-Degree Days (CDD) parameter was used as a measurement of the ability of the experimental fish (Oreochromis niloticus, Sarotherodon gallilius and Tilapia zillii) to tolerate low water temperatures. In addition, the genotyping of UNH118 SSR candidate associated to the cold tolerance trait was studied. Finally, we tried to find out if the CDD response of each species could be explained due to the variation found from the tested UNH118 SSR locus. O. niloticus demonstrated the highest number of alleles (5) was the only species that was significantly correlated to its recorded CDD values (r-value = 0.91, p-value = 0.04). However numerically the T. zillii was showed to be the most tolerant tilapia species down to 6.5 ºC (CDD = 143). While in case of O. niloticus and S. galilaeus, the CDD values for the last dead fish were 116 and 104, respectively.
Differential display technique was also used to detect mRNAs that are differentially expressed in hepatic tissues of T. zillii fish subjected to a temperature reduction regime that combined both an accelerated and a stationary cold stresses. Two arbitrary differentially expressed primers (DD1 and DD2) were used and generated a total of 375 and 291 unknown messenger RNA (UmR) bands respectively. Each primer scored 38 and 20 significantly expressed fragments after refining respectively. The detected UmRs were Categorized as: (1) Up-regulated genes (2 and 4 for DD1 and DD2 respectively); (2) Down-regulated genes (8 and 0 for DD1 and DD2 respectively); (3) Genes expressed in all the sampled states and showed changes in their expression profile (5 and 10); (4) Genes expressed only in the stationary phase (20 and 2); (5) Genes expressed only during the accelerated phase and degraded before the stationary phase (2 and 1); (6) Genes expressed during the accelerated phase and degraded in a slower rate during the initiation of the stationary phase (1 and 3). Thus, T. zillii was proven to be the most tolerant species among the Egyptian Tilapias followed by O. niloticus species while the S. galilaeus showed the lowest cold tolerance ability. In addition, T. zillii responded to low temperature by adjusting expression of a set of genes to make adaptation.