Histopathology of the Digestive Tissues and Whole-Body Anaerobic Bacteria Counts of the Eastern Oyster, Crassostrea virginica, After Experimental Exposure to Anoxia

ABSTRACT The Eastern oyster, Crassostrea virginica, is a sensitive bio-indicator of environmental changes ranging from tidal flux to heavy-metal pollution. Extreme fluctuations in dissolved oxygen levels are well documented in Mobile Bay, AL. Extended periods of low dissolved oxygen occurring during the summer months have been shown to cause oyster mortality. The current study examined the effects of anoxia on tubule morphology of the digestive gland in the Eastern oyster as well as the quantity and quality of whole-body anaerobic bacteria counts. Oysters were exposed to anoxic conditions (<0.1 mg/L O2) at 28°C in a laboratory setting and sampled at 0 h (preexposure), 24 h, 48 h, and 60 h, and after a 4-wk recovery interval. The whole-body anaerobic bacteria count for test oysters (Mean = 1.11 × 106 cfu/mL) from the 60-h interval was significantly higher than counts for the preexposure oysters, 24-h, and 48-h experimental intervals. The most common bacteria isolated were Clostridium sp. Histological exami...