Glutathione S-transferase and metallothionein levels in the freshwater prawn Macrobrachium malcolmsonii exposed to mercury.

ABSTRACT

Healthy juveniles of M. malcolmsonii were exposed to 24.1 <g l-1 of mercury (96 hr LC50 145 <g l-1 Hg) for a period of 21 days. The hepatopancreas and gills of the prawns were sampled on 8th, 15th and 22nd day of exposure. Accumulation and elimination of Hg, activity of glutathione S-transferase (GST), content of glutathione (GSH) and metallothionein (MT) level were studied. Mercury accumulation was found to be higher in the hepatopancreas (88.60 <g g-1) and lower in the gills (67.8 <g g-1). However, Hg elimination was found to be faster in the gills (62%) and slower in the hepatopancreas (58%). Therefore, the rate of Hg elimination did not match the rate of its uptake. The activity of GST was found to be higher in tissues of test prawns (5.94-9.13 nmol mg-1 protein min-1) on all sampling days when compared with controls (3.45-4.23 nmol mg-1 protein min-1). Similarly, the content of GSH was found to be higher in tissues of test prawns (0.80-1.43 <mol g-1 protein) on all sampling days when compared with controls (0.55-1.00 <mol g-1 protein). These results indicate the formation of glutathione conjugate in test prawns to eliminate Hg. The induction of MT level was also found to be higher in tissues of test prawns (57.50-75.76 nmol g-1 protein) on all sampling days when compared with control (20.24-45.22 nmol g-1 protein). This indicates the fact that sequestration of Hg has occurred for its easy elimination. Thus, induction of GST-GSH and MT ensured protection and adaptation of test prawns to thrive in Hg contaminated environment.