Development of Tilapia PCR Arrays for Pollutant Exposure Monitoring in the Tropical Freshwaters (A case study in Nigeria)

Abstract

Pollutants contaminate both marine and freshwater systems and are known to regulate animals’ metabolic pathways. Chemicals are discharged through industrial waste, sewage, agricultural and urban run offs, which, reach aquatic ecosystems and impact organisms including fish. This research investigated the effects of xenobiotics on selected genes using QPCR arrays. Six tissues were chosen from adult Nile tilapia and validated using 28 genes already optimised by Real transcriptase quantitative polymerase chain reaction (RT-qPCR). Nile tilapia (Oreochromis niloticus) prefeeding larvae (6-7 dpf) was used as a model species and exposed to different sub-lethal concentrations of ten environmental relevant chemicals in the laboratory using RT- qPCR. Primers sequences of the already selected and optimised genes that passed the quality criteria were used in the assay (AHR 2, CYP 1A, DIABLO 1 and 2, GST01LA, GSTA2L, GSTMA, GSTR2, MT AND VTG). Wild tilapia samples were caught at both the polluted Dan Agundi and Daberam sites and the clean Jibia site and the length-weight relationship and condition factor established. The results indicated that ten of the twenty-eight assays results were within the target amplification efficiencies and coefficient of correlation ranges of 0.90-1.10% and 0.9-0.99 respectively. Most of the genes showed expression in the liver. In the laboratory exposure, different chemicals induced significant mRNA gene expressions, including aryl hydrocarbon receptor and estrogen receptor pathways, phase II biotransformation, apoptosis and metal toxicity in the larvae. While in the field, significant statistical changes in the expression of genes involved in different physiological and metabolic signalling pathways were observed. Different length-weight relationship and the condition factor were also observed in both the polluted and non-polluted sites. The use of biomarkers can provide valuable knowledge of the effects of pollutant mixtures on the aquatic ecosystem and the risks to exposed organisms, especially fish.