Naturally, aquatic organisms have self-defense mechanisms that protect them from the actions of endocrine disrupting chemicals (EDCs) such as the herbicide and antimicrobial Glyphosate (GLY) . The changes in expression levels of different types of enzymes could be used as biomarkers of GLY exposure such as hepatopancreatic cytochrome P450-associated enzyme activity. It is also possible that the rate of release of reactive oxygen species (ROS) increased during GLY exposure, and the defense mechanisms occurred in the cell because of rapid oxidation, reduction, hydroxylation and dealkylation reactions. Glyphosate 41% S.L. (I.P.A salt, 500ml) manufactured by Monsanto India Limited, Mumbai, India was used in this study. GLY was purchased at Theni district, Tamilnadu . The 41% GLY was used to prepare 100% stock and serially diluted t o different concentrations (10ppm, 20ppm, 30ppm, 40ppm, and 50ppm) . The effect of Glyphosate exposure was examined to assess the oxidative stress and biotransformation of P. vannamei post larval stage (PL12–PL15) collected from a commercial farm near Pattukkottai , Thanjavur District, Tamilnadu, and acclimatized for one day before the experiment started . After measuring body length (1.760 ±0.197cm) using Verni er caliper and weight (0.629±0.081g) they were divided into six groups (n=25/tank): control, 10ppm, 20ppm, 30ppm, 40ppm, and 50ppm GLY, for 24hours. Water quality was maintained at pH 7.8, salinity of 28-32ppt and temperature of 27-28ºC throughout the study. Tissue samples were collected every 6hr and the hepatopancreas removed for enzymatic reactions.
The levels of antioxidant [superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR)] and biotransformation enzymes (CYP450 isoform-EROD, MROD, BROD and GST) increased at 6hr and 12hr in the 10ppm -30ppm GLY groups, their activity decreased afterwards. In the 40ppm -50ppm GLY groups, the antioxidant and biotransformation enzymes increased up to 24hr.
Results suggested that (a) antioxidant enzymes were elevated at early stages of exposure in 10-30ppm groups, (b) GR , SOD and CAT play a crucial role against ROS and neutralized by them , (c) enzymatic biotransformation is essential to eliminate GLY, and (d) the cellular enzyme defense mechanism protect shrimp at certain levels of exposure.