Abstract

Nile tilapia (Oreochromis niloticus) is considered as one of the most economical and popular aquaculture species. One of the main concerns in tilapia aquaculture, as well as in the wild, is growth, because of its importance for the fish population, stock assessment and their production in aquaculture. Accordingly, this study was initiated to characterize growth on molecular basis. In the same respect, RNA/DNA ratio and GHR-1/IGF-1as growth-related genes are known to be involved in weight gain alterations. To assess the correlation between growth, biochemical and hormonal conditions of fish during summer and winter. Adult male O. niloticus (100 - 250gm) were collected from Bahr Shebeen Canal, for such investigation. The results revealed that the GHR-1 and IGF-1 mRNA were directly proportional to age, length and weight. However, they were up regulated in summer than in winter. However, RNA/DNA ratio gave an observable positive correlation with age and length only with higher values in winter. In conclusion, this study supports the use of GHR-1/IGF-1as reliable indices of growth and condition of O. niloticus in their natural habitat in addition to RNA/DNA ratio assessment.

Key words: Oreochromis niloticus, GHR-1, IGF-1, seasonal variation, RNA/DNA ratio