With a global farmed production of more than 6 million tons annually, the tropical cichlid Nile tilapia (Oreochromis niloticus) is one of the most important farmed fish species worldwide, with Egypt being the leading producer on the African continent. Monitoring of water pollution by chemical analysis alone cannot completely assess the effects of the pollutants on aquatic species because of the high number of unknown chemicals and the mixture presence of these chemicals. In contrast, the use of pollutant-responsive biomarkers in fish can be an effective approach to monitor water pollution, as this provides a more comprehensive and realistic assessment of the exposure and response of aquatic organisms to chemical stressors.
Molecular biomarkers are used as a tool to quantitatively measure a sub- organismal change, including apoptosis, DNA damage, micronucleus formation and gene expression changes, within organisms in response to external chemical stress. In this context, fish larvae may offer a suitable model for studying the effects of water pollutants.
Our aim is to develop an array of gene expression biomarkers in Nile tilapia larvae that can detect environmentally relevant concentration of water contaminants of different mechanisms of action (Figure 1)
A total of 1101 genes (226 up-regulated and 875 down-regulated) were identified by gene expression profiling using RNA-Seq (figure 2)
The results of GO and KEGG enrichment analyses indicated a disruption of the immune system, particularly the induction of apoptosis, inflammation, oxidative stress, and autoimmunity in addition to biological processes involved in detoxification. Also, there was a significant inhibition of neuronal developmental pathways displayed with some of these contaminants (Figure 3)