Effects of X- and gamma irradiation on the juvenile pacific oyster, Crassostrea gigas Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/2n49t421r

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  • Two separate studies were conducted during this research project. Oysters were irradiated with 500 and 1000 rads and 5, 10, 20, 50, 75, 100, 150, and 200 krads in the first study in order to determine the effects of ionizing radiation on survival and growth rates. Two periods of high mortality were noted; the first occurred from 2 to 7 days postirradiation in oysters receiving 75 to 200 krads and was associated with an "acute lethal tissue degenerative syndrome." The second mortality period occurred from 40 to 60 days postirradiation in oysters exposed to 10 krads or more and was caused by a "lethal tissue degenerative syndrome." The LD-50 dose was found to be a complex function of time from the moment of irradiation until approximately 80 days postirradiation. The 238-day LD-50 value was 16.5 krads. The mean wet weight of oysters exposed to 20 krads was significantly less than that of the controls from 167 to 238 days postirradiation. Analysis of the results suggest a dose dependent wet-weight relationship in the 5 and 10-krad oysters; they did not weigh significantly less than the controls. Although not statistically significant, the mean wet weights of oysters exposed to 500 and 1000 rads exceeded that of the controls from 43 to 238 days postirradiation. In the second study, oysters were irradiated with 200 R, 600 R, 1000 R, 5 kR (X irradiation), and 8, 16, and 40 krads (gamma irradiation). The purposes of the second study were to analyze histopathologically, the degenerative syndromes and subsequent tissue repair processes in the stomach, gut, collecting ducts, and digestive tubules. Degenerative changes were seen only in the digestive tubules of 5- and 8-kR oysters while in oysters exposed to 16 and 40 krads, degenerative changes coincided with the lethal tissue degenerative syndrome noted in the survival-wet weight study. A tissue regeneration sequence was observed in the stomach, gut, collecting ducts, and digestive tubules of most oysters exposed to 16 krads and in a smaller number of oysters exposed to 40 krads. Tissue regeneration was first observed in the digestive tubules and subsequently in the stomach, gut, and collecting ducts. Repopulation of the digestive tubules involved reepithelialization of the tubule with large, undifferentiated crypt cells followed by their differentiation into secretory and absorptive cells. Tissue recovery in the stomach, gut, and collecting ducts was initiated by islands of small basophilic cells not previously described in these tissues. Rapid mitotic proliferation of these cells and their subsequent differentiation into basal epithelial cells, resulted in the reepithelialization and eventual recovery of these tissues.
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