THE EFFECT OF IONIZING RADIATION 

 ON THE THERMAL TOLERANCE 

 OF MOSQUITOFISH 



B. G. BLAYLOCK and M. L. FRANK 



Oak Ridge National Laboratory, Environmental Sciences Division, Oak Ridge, 



Tennessee 



ABSTRACT 



This study determined the effects of acute ionizing radiation on the thermal 

 tolerance of the mosquitofish, Gambusia affinis. Gambusia of approximately the 

 same size w^ere given doses of radiation ranging from 500 to 5000 rads from a 

 Co source. The irradiated fish w^ere tested 5, 15, and 30 days after irradiation 

 for either lethal temperature w^ith a critical thermal maximum (CTM) type test 

 or mean survival time in a lethal temperature bath (39.5 C). The lethal 

 temperature for Gambusia irradiated w^ith 500 rads was not significantly 

 different from that of control fish; neither were lethal temperatures for fish 

 irradiated with 1500 rads and tested at 5 and 30 days after irradiation. At day 

 15 and 1500 rads, however, lethal temperature was significantly reduced. At a 

 dose of 1500 rads, histopathological effects were observed in the hematopoietic 

 tissues of Gambusia 5 days after irradiation; regeneration of the tissue began by 

 day 15 and continued through day 30. The mean survival time of Gambusia was 

 not affected by a dose of 500 rads; but, at doses of 1500 rads and above, the 

 effect was significantly different at day 5. A significant difference was also 

 detected at day 15 for the fish receiving a 1500-rad dose. Recovery had taken 

 place by day 30, however, and the mean survival times were not significantly 

 different from controls. 



The effects of the interaction of temperature and irradiation on 

 aquatic organisms have been examined by several investigators. 

 Essentially all these studies have been directed toward determining 

 the effects of low sublethal temperatures on the expression of 

 radiation effects. Gros and Bloch (1957) and Gros et al. (1958) 

 hypothesized that low temperature protects against radiation dam- 

 age. Some subsequent studies (Egami and Etoh, 1966; Etoh and 

 Egami, 1965; Angelovic, White, and Davis, 1969) showed that 



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