Mercury pollution assessment and metallothionein gene expression in tilapia ( Oreochromis mossambicus ): a case study of Revuè River in Manica, Mozambique

Revuè River has been considered as one of the most threatened systems in Mozambique due to increased anthropogenic activities such as artisanal and industrial gold mining using mercury (Hg), a heavy metal known for its diverse effects including, bioaccumulation and biomagnification in the environment. The present study aims to determine the metallothionein (MT) expressions in the hepatic tissue of Oreochromis mossambicus (tilapia) exposed to Hg in the laboratory and tilapia collected in Chicamba reservoir. Tilapia juveniles were exposed to different concentrations of Hg (0.037 and 0.37 mg/L) in the laboratory. Water, sediment and fish samples were collected to quantify Total Hg (THg). Furthermore, liver samples in tilapia exposed to Hg and tilapia samples from Chicamba reservoir were collected to analyze the gene expression levels of MT using a quantitative PCR. Results from the study showed a low contamination of the waters and sediment from Revuè River, demonstrated by the Hg concentration in the sediment and water. Slightly high concentrations of Hg were detected in fish from Chicamba reservoir, confirmed by the overexpression of MT observed in liver samples from tilapia and were higher than those expressed in tilapia from the laboratory experiment. There is a correlation between Hg exposure and the MT expression in tilapia, suggesting that MT can be used as a biomarker to assess Hg pollution in the Revuè River.