THERMAL STRESS OF AMBIENT TEMPERATURE MODULATE EXPRESSION OF STRESS AND IMMUNE-RELATED GENES AND DNA FRAGMENTATION IN NILE TILAPIA (OREOCHROMIS NILOTICUS (LINNAEUS, 1758))

Owing to its cold-blooded nature, water temperature is a driving force in fish life. The aim of this study is to explore the effect of the thermal stress of ambient temperature during summer and winter in Nile tilapia (Oreochromis niloticus) on heat shock proteins (HSP70, HSP27), oxidative stress genes (MT and GST) and some immune response genes (IL-1, IL-8, and TLR7). As well as to compare the DNA fragmentation at both variant temperatures using RAPD-PCR and micronucleus assay. The fish were collected twice, once at the end of December (winter sample, temperature 14 degrees C), and the other at August (summer sample, temperature 36 degrees C). qRT-PCR analysis of mRNA expression for the studied genes were done. HSP70 expression increased equally in gills and liver at both summer and winter, suggesting its advantageous role in fish survival in the labile environment. Its expression exceeds HSP27 level, whose expression increased in summer. GST expression increased in summer in liver than gills and expressed equally at both organs in winter. No differences were observed in MT and immune response related gene expression in both seasons. The very close pattern of RAPD-DNA fragmentation and micronuclei were recorded at both thermal stresses. We conclude that, thermal stress of cold and hot extremes of ambient temperature in Nile tilapia have a nearby role in expression of HSP70, MT, liver GST and immune response related genes. As well as the incidence of micronucleus and DNA fragmentation.