Bacterial depuration of grossly-contaminated oysters, Crassostrea iredalei.

Abstract

Oysters (Crassostrea iredalei ) from a commercial growing area in Capiz, Iloilo, Philippines, were purchased from the Iloilo City Central Market and used in a depuration trial within 24 hours of collection. Total coliform (TC) and fecal coliform (FC) levels were determined using the five-tube, most probable number (MPN) technique. Samplings were carried out in three areas in the tank: (a) near the water trickle are, (b) at the middle and (c) near the water outflow area. FC proved to be a better and more consistent indicator of depuration efficiency than TC which gave erratic levels in the first 24 hours. The oysters with initial FC MPN of 2.2 x 10 super(5)/100 g meat depurated to acceptable levels (< 230 MPN/100 g meat) after 48 hours except those in the middle of the tank (490 MPN/100 g). This suggests the presence of an "indifferent" or "dead" spot. Nevertheless, the same oysters depurated successfully within 72 hours. Ranges of chemical and physical parameters in the depuration water were: temperature, 27.0-29.5 degree C; salinity, 30.5-32.0 ppt; and dissolved oxygen, 4.0-6.2 mg/l.