Depuration of Bacterial Populations in the Indian Backwater Oyster Crassostrea madrasensis (Preston, 1916): Effects on Surface and Bottom Held Oysters

Chinnadurai, S and Mohamed, K S and Venkatesan, V and Jenni, B and Kripa, V (2014) Depuration of Bacterial Populations in the Indian Backwater Oyster Crassostrea madrasensis (Preston, 1916): Effects on Surface and Bottom Held Oysters. Journal of Shellfish Research, 33 (2). pp. 409-414.

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Abstract

The efficiency of depuration of the Indian backwater oyster Crassostrea madrasensis (Preston, 1916) using the filldraw method (static method) with high-loading density was evaluated in this study. Depuration experiments were conducted with cartridge-filtered and UV-treated seawater at a salinity of 30.3&, a pH of 8.3, and a temperature of 29.5C. The oysters located in trays on the surface and on the bottomwere compared formicrobial loads. Samples were taken at 0 h, 8 h, 16 h, 24 h, 36 h, and 48 h of depuration. The results showed that in wintermonsoon-sampled nondepurated oysters, themost probable number of fecal coliforms and Escherichia coli were greater than the limits according to NSSP and European Union regulations. The surface held oysters took 24 h to reduce the coliforms and E. coli levels to belowsafe limitswhereas for bottomheld oysters it took 48 h. The species Salmonella was never detected in the oysters sampled, whereas Vibrio spp. were present in the nondepurated oysters and were eliminated completely after 8 h of depuration. Variation in depuration of total coliforms, fecal coliforms, E. coli, total plate count, and fecal streptococci in oysterswere significant (P < 0.05) between surface and bottomoysters. The study results recommend a loading density of 2 oysters/L water stacked in 1 layer as the optimum loading density for commercial depuration completed within 24 h.

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