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Biomarkers and pollutants in the Nile Tilapia, Oreochromis niloticus, in four lakes from San Miguel, Chiapas, Mexico

The effects of the oil industry and environmental pollutants present in four lakes from Reforma, Chiapas, Mexico, were assessed via ethoxyresorufin O-deethylase activity (EROD), PAH metabolites, and butyrylcholinesterase activity (BChE) in Nile Tilapia, Oreochromis niloticus. Fish were collected during two seasons (the rainy season in September 2000 and the dry season in May 2002) from the lakes Caracol, Rio, Enmedio, and Limon. Fish were sacrificed and EROD activities, hydrocarbons, organochlorine pesticide and heavy metal concentrations were determined in the liver, while PAH metabolites and cholinesterase activity were measured in bile and muscle, respectively. Hydrocarbon concentrations in fish liver were moderately high, as compared with results reported for the other species in different coastal ecosystems in Mexico. The highest concentrations of total hydrocarbons were found in fish captured in Lake Limon, and the lowest in Lake Caracol. The highest EROD and PAH metabolites were found in fish collected from Limon and Enmedio lakes. A Spearman test showed significant negative correlations between EROD and BChE activity with fish weight. EROD correlated with total hydrocarbons, the metabolites of pyrene and benzo[a]pyrene, and negatively with polychlorinated biphenyls (PCBs), endosulphan, hexachlorobenzene (HCB), and pentachloroanisol. BChE activity in the four lakes was lower than the activity measured in laboratory cultured tilapias, indicating the presence of anti-cholinergic pollutants in the area; Caracol was the lake with the lowest enzyme activity. This study demonstrated that high concentrations of contaminants can cause effects on fish metabolism, and that tilapia can be used as a test organism in tropical ecosystems.

Keywords: biomarkers, hydrocarbons, organochlorine pesticides, PAH metabolites, polynuclear aromatic hydrocarbons, heavy metals, tilapia, Oreochromis niloticus, lakes, water pollution, oil industry, fish metabolism, environmental pollution, Mexico, cholinesterase activity, PCBs, anti-cholinergic pollutants, tropical ecosystems

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