K. Kavya¹ , A. Raj¹ , A. Suresh¹ , A. A. Mohamed Hatha^1,2

1 Department of Marine Biology, Microbiology and Biochemistry, School of Marine Sciences, Cochin University of Science and Technology (CUSAT), Kochi 682016, Kerala, India
2 CUSAT-NCPOR Centre for Polar Sciences, School of Marine Sciences, Cochin University of Science and Technology (CUSAT), Kochi 682016, Kerala, India
Author    Correspondence author
International Journal of Aquaculture, 2026, Vol. 16, No. 3   
Received: 23 Mar., 2026    Accepted: 25 May, 2026    Published: 15 Jun., 2026

This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

This study evaluated the effectiveness of a closed water depuration system equipped with a sponge filter for reducing bacterial contamination in black clams (Villorita cyprinoides) harvested from the Varapuzha region of the Cochin Estuary, Kerala, India. Initial bacteriological analysis revealed high levels of contamination in the clams, indicating potential food safety risks for consumers. The depuration experiment was conducted in a recirculating tank system fitted with a sponge filter, in which clams were maintained in clean water and sampled at regular time intervals up to 72 hours. Bacterial indicator reduction, including Total Coliforms (TC), Faecal Coliforms (FC), Total Heterotrophic Bacteria (THB), and Vibrio species were monitored to evaluate the purification efficiency of the system. Results demonstrated a marked reduction in bacterial load during depuration, with the most pronounced decrease occurring within the first 48 hours. Total coliforms and faecal coliforms were reduced by 98.54% and 98.45%, respectively, reaching  substantially lower faecal indicator levels, although compliance with specific regulatory standards requires validation using the prescribed indicator organisms and units. Total heterotrophic bacteria also showed a substantial decline, while Vibrio species were reduced to a lesser extent. Nevertheless, a gradual increase in bacterial counts was observed on the inner walls of the depuration tank due to biofilm formation, indicating the possibility of recontamination if the system is not properly cleaned. Overall, the sponge filter-based closed water depuration system proved to be a simple, cost-effective, and water-efficient method for improving the microbiological quality of clams. This approach is suitable for small-scale depuration practices and could help to improve shellfish safety and protect public health. This study may provide practical baseline information for optimising low-cost shellfish depuration systems under tropical estuarine conditions.

Depuration; Black clam (Villorita cyprinoides); Sponge filter; Bacterial reduction; Biofilm; Closed water depuration system