Nova Biotechnol Chim (20xx) xx(x): e824 DOI: 10.36547/nbc.824 1 Nova Biotechnologica et Chimica Depuration of a freshwater clam (Batissa violacea) from Rewa River in Fiji using a bio-filter set-up in closed and open water circulatory system Ashneel Ajay Singh 1,2, , Ravinesh Ram 3 , Sheemal Vandhana Kumar 2 , Sheenal Aashna 2 , Shipaldika Verma 2 , Zafiar Tasmeen Naaz 2 , A. A. Mohamed Hatha 4 1 School of Agriculture, Geography, Environment, Ocean and Natural Sciences, The University of the South Pacific, Suva, Fiji 2 Department of Science, School of Science and Technology, The University of Fiji, Lautoka, Fiji 3 Department of Fisheries, College of Agriculture, Fisheries and Forestry, Fiji National University, Koronivia, Fiji 4 Department of Marine Biology, Microbiology and Biochemistry, Cochin University of Science and Technology, Kerala, India  Corresponding author: ajaymsp1@gmail.com Article info Article history: Received: 18 th January 2021 Accepted: 21 st May 2021 Keywords: Aerobic plate count Batissa violacea Biofilter Bivalve Coliform Depuration Abstract The effectiveness of the freshwater bivalve Batissa violacea depuration was tested in closed and open water circulatory system over a 48 h period. The closed circulatory system included a sand biofilter. Microbial levels were assessed every 4 h using Total Aerobic Plate Count (TPC) for heterotrophs and Most Probable Number (MPN) for coliforms. TPC and coliform loads in bivalve tissue reduced rapidly to low and undetectable levels in a closed circulatory system while open system showed a slower reduction. Both TPC and coliform loads remained above detectable levels throughout the depuration period. Closed system showed similar patterns of logarithmic reduction of TPC and coliforms in all cases with R 2 >0.95 and p<0.001. Similar results were observed for tank water however, reduction of TPC and coliforms were slower. Biofilm formation was observed in the interior walls of the aquarium tanks over 48 h in all cases. Physicochemical parameters did not show any significant change. The reduction in TPC and coliform load in B. violacea suggests that biofilter in a closed water circulatory system is a simple, cost-effective, water conserving and effective way to significantly reduce the spoilage and coliform bacterial load that is accumulated in the clams.  University of SS. Cyril and Methodius in Trnava Introduction Pacific Island Countries (PICs) have a large proportion of populations residing near natural water bodies including the coastal and river systems (Andrew et al. 2019). These populations generally have heavy socio-economic and subsistence dependence on these coastal resources from these sources including Fiji (Waqalevu 2015; Andrew et al. 2019). Bivalves are known as a rich source of protein and are highly perishable in untreated form which hinders the process of transport and storage (Frazier and WestHoff 2000; Udoh et al. 2017). Shellfish-borne bacterial and viral diseases are one of the major concerns for public health (Botana 2014). Bivalves accumulate heavy metal toxins and various pathogens from fecally contaminated natural water during their filter feeding behaviour (Hatha et al. 2005a; Botana 2014; Waqalevu 2015). Therefore, inappropriate disposal of raw and partially treated sewage into the natural water