International Journal of Research Publication and Reviews Vol (2) Issue (4) (2021) Page 10-18 International Journal of Research Publication and Reviews Journal homepage: www.ijrpr.com ISSN 2582-7421 * Corresponding author. E-mail address: Kasunthia@ocu.ac.lk Cholinesterase (ChE) and Glutathione S- transferase (GST) enzyme activitiesof the brackish water clam, Meretrixcasta inhabiting selected estuaries in Sri Lanka E.A.K.K. Amarasekara 1, 2 , A. Pathiratne 1 , T.B. Wanninayake 3 1 Department of Zoology, Faculty of Science, University of Kelaniya, Kelaniya, Sri Lanka 2 Department of Coastal and Marine resources Management, Faculty of Engineering and Management, Ocean University of Sri Lanka, Colombo 15, Sri Lanka 3 Department of Aquaculture and Fisheries, Faculty of Livestock, Fisheries and Nutrition, Wayamba University of Sri Lanka, Makandura, Gonawila. A B S T R A C T 1. Environmental pollutants such as metals, pesticides, and other organics pose serious risks to many aquatic organisms.Bivalve are filter feeding bio accumulators that have been used as sentinel organisms in numerous monitoring programs. The activity of glutathione S-transferase (GST) and cholinesterase (ChE) was evaluated in the gills of the wild populations of Meretrixcasta inhabiting selected estuarine environments namely Mundalama in Mundal Lake, Marawala in Chilaw estuary, Pitipana and Pamunugama in Negombo estuary of Sri Lanka and to evaluate whether they are safe for human consumption. The clams were sampled from each site monthly during the period, September 2007 to May 2008.Therefore, the aim of this study was to investigate possible changes in two widely used biomarkers, the activity of the enzymes cholinesterases (ChE) and glutathione S-transferases (GST), of Meretrixcastafrom wild populations of the selected sites.The results showed that mean ChE activities of the gills of the clams collected from Mundalama, Marawala and Pamunugama were significantly higher than that of clams from Pitipana.When comparing the monthly variations during the study period, in months of April and May 2008, ChE activities of the gills of clams collected from Mundalama, Marawala and Pamunugama sites were higher in comparison to the ChE activities in the clams collected from the respective sites during the other sampling periods. No significant correlations were found between the ChE activities of the clams collected from the sites with individual environmental parameters, except in the site Pitipana where lead level in sediment samples was negatively correlated with the gill ChE activity of the clams. October 2007, clams collected from Pamunugama site showed the highest GST activity, but in the other months GST activity did not vary much site-wise. No significant correlations were found between the GST activities and theenvironmental parameters tested.Effects showed that gillChE and GST activities were infected by environmental factors, which indicate neurotoxic and detoxification capacities of the clams shows changing the patterns of the ChE and GST activities.Results of the present study revealed the clams in selected study sites of the three estuaries are safe for human consumption.Furthermore, the present study highlights the need of long-term monitoring with wild populations to assess effects of environmental pollution in the estuarine environmentfor sustainable exploitation of these resources as food and non-food sources. Keywords: Brackish water Clam, Cholinesterase, Glutathione S- transferase, Physiological responses, Sri Lanka 1. Introduction Physiological effects of environmental stress are numerous. While the ultimate end point of stress is mortality, sub-lethal stress may interfere with the normal physiological activities of the animals such as impairments in neurological functions, detoxification capacities and increased expenditure of energy