First report on fish cysteine as a biomarker of contamination in the River Chenab, Pakistan.

The eastern and southern parts of the Faisalabad city produce considerable quantities of industrial and municipal pollutants, much of which is drained into the River Chenab, reducing the productivity of fauna and flora in the river. This study was aimed to determine whether cysteine is useful as a biomarker of exposure to polluted fresh water. The amino acid profile of fish muscle was analyzed by paper chromatography in Cirrhinus mrigala and Labeo rohita from the River Chenab to determine habitat related variations due to the pollution from industrial and domestic sources. C. mrigala showed higher level of metal contamination in muscle tissues for Sn, Cr, Pb, Zn, Mn, Cu, and Cd when compared to L. rohita. Both fish species collected from polluted areas of the river Chenab showed significantly (P < 0.01) higher levels of metals in comparison to upstream and farmed fish. Farmed C. mrigala showed cysteine concentrations in the muscle tissue as 22 ± 1 mg/g dry weight, but concentrations increased to 45 ± 2 mg/g dry weight for fish from a mildly polluted section of the river, and further increased to 83 ± 2 mg/g dry weight in more heavily polluted sections. Cysteine concentration in farmed L. rohita was detected as 28 ± 2 and 25 ± 4 mg/g dry weight, respectively for farmed fish and fish from a mildly polluted section of the river, and then increased to 94 ± 3 mg/g dry weight for fish from highly polluted water. C. mrigala from a mildly polluted area of the river also had higher levels of cysteine in the muscle, along with increases in aspartic acid, glutamic acid, and alanine. Elevated concentrations of cysteine seem to be associated with a threat to these fish species in polluted sections of the river, and thus may be used as a biomarker.