Methylparathion (MP) is an organophosphorus insecticide used world wide in
agriculture due to its high activity against a broad spectrum of insect pests. The
aim of the study is to understand the effect of methylparathion on the lipid
peroxidation, detoxifying and antioxidant enzymes namely catalase (CAT),
glutathione peroxidase (GPx), superoxide dismutase (SOD), glutathione Stransferase
(GST), total reduced glutathione (GSH), lipid peroxidation (LPO),
acetylcholinesterase (AChE) and disease diagnostic marker enzymes in liver,
sarcoplasmic (SP) and myofirbirllar (MF) proteins in muscles, lipids and
histopathlogical changes in various organs of Labeo rohita of size 75 i 6g at
lethal and sublethal level of exposure. The probit analysis showed that the lethal
concentration (LC 50%) for 24, 48, 72 and 96h were 15.5mg/L, 12.3mg/L,
11.4mg/L and 10.2mg/L respectively which is much higher compared to the LC50
for juvenile fish. The LPO level and GST activity increased five folds and two
folds respectively on exposure to methylparathion at 10.2 mg/L and the level of
the enzymes increased, on sub lethal exposure beyond 0.25mg/L. AChE activity
was inhibited by 74% at a concentration of 1.8mg/L and 90% at 5.4mg/L. The
disease diagnostic marker enzymes AST, ALT, ALP and LDH increased by about
2, 3 ,3 and 2 folds respectively at pesticide concentration of 10.2mg/L when
compared to control. On sub lethal exposure, however the enzymes did not show
any significant changes up to 0.5mg/L. At a concentration of 10.2 mg/L, there
was a three fold increase in myofibrillar proteins while the increase in
sarcoplasmic protein was above 1.5 fold. On sub lethal exposure, significant alteration was noticed up to 30 days up to 1mg/L of methylparathion
concentration. Further exposure up to 45 days increased sarcoplasmic proteins
(upto 0.5mg/L). ln the case of myofibrillar proteins, noticeable changes were
observed at 1mg/L concentration right from 15th day. The cholesterol content in
brain tissues increased by about 27% at methylparathion concentration of 5.4
mglL. However at 0.25mg/L sub lethal concentration, no significant alteration was
observed in enzyme activity, muscle proteins, lipids and histopathology of the
tissues. The results suggest that methylparathion has the potential to induce
oxidative stress in fish, and that liver, muscle and brains are more sensitive
organs of Labeo rohita, with poor antioxidant potentials at higher concentrations
of the pesticide. The various parameters studied in this investigation can also be
used as biomarkers of methylparathion exposure.Dept.of Chemical Ocenography,Cochin University of Science and Technolog
