Chapter 10 



Radiation of Aquatic Organisms 



97 



order of magnitude as that of other cold- 

 blooded vertebrates. 



B. Relative sensitivity of different stages of 

 development 

 It must be recognized in any consideration of 

 the relative sensitivity to radiation of different 

 groups of organisms that considerable varia- 

 bility exists between similar species. In com- 

 paring the sensitivity of two species of snails, 

 Bonham and Palumbo (1951) found that "at 

 10 kr, approximately one month elapsed before 

 50 per cent of the Radix died, while in the case 

 of the Thais it was approximately one-half of a 



later stages of development. Unpublished work 

 by Welander has shown the most radiation- 

 sensitive period of silver salmon {Oncorhyn- 

 chus kisutch) egg development to be a par- 

 ticular stage during the mitosis of the single 

 cell. For the most sensitive period an LD50 o^ 

 only about 16 roentgens was observed. 



The change in sensitivity between different 

 stages of development has also been shown with 

 snails. Bonham and Palumbo (1951) showed 

 that eggs of the fresh- water snail Radix japonica 

 were more sensitive to radiation than the adults. 

 Further studies of snails (Helisoma subcre- 



TABLE 2 Relative Sensitivity of Different Life Stages of Salmonoids 



Stage 

 irradiated Species 



Gametes ^ rainbow trout 



Eyed eggs chinook salmon 



Fingerlings chinook salmon 



Adult rainbow trout 



1 In parent fish. 



year." Consideration must also be given to the 

 different developmental stages of the same spe- 

 cies. Since many investigators (Evans, 1936, 

 Rugh, 1949) have correlated radiosensitivity 

 with metabolic rate of the dividing cell, it is not 

 surprising that dormant eggs of aquatic inverte- 

 brates should be especially resistant. Bonham 

 and Palumbo (1951) found that the two-week 

 LD50 for dry Artemia eggs was about 50,000 

 roentgens, but after soaking the eggs for a short 

 time in water, so that embryonic development 

 was resumed, the radiosensitivity increased more 

 than twofold. 



A review of the results of exposing salmo- 

 noid gametes, eggs, fingerlings or adults to 

 X-radiation supports the early concepts (Butler, 

 1936) that radiosensitivity decreases with age. 

 Table 2 shows that the LD50 values range from 

 50-100 roentgens for gametes within the parent 

 fish to about 1500 roentgens for adult trout. 

 Welander (1954) studied in detail the effects 

 of X-rays on different embryonic stages of rain- 

 bow trout. His results with these aquatic forms 

 confirmed the work of Russell and Russell 

 (1954) and others working with mammals that 

 certain critical periods exist during which the 

 embryo is most sensitive to radiation. Table 3 

 shows some of Welander's data. 



Trout eggs were much more sensitive to ra- 

 diation during the one-cell stage than during 



Approximate 

 median effective 

 dose (LD50) 

 50- 100 r 

 1000 r 

 1250-25001 

 1500 r 



Investigator 

 Foster, et al. (1949) 

 Welander, et al. (1948) 

 Bonham, et al. (1948) 

 Welander, et al. (1949) 



natum) eggs by Bonham (1955) showed that, 

 in the one- and two-cell stages, resting eggs 

 withstood from two to four times as much radia- 

 tion as cells undergoing mitosis, and that later 

 embryonic stages were less sensitive. 

 C. Pathology of radiation damage 

 1. Different organs 



While effects of exposure to larger amounts 

 of radiation than that sufficient to cause death of 

 the organism have been studied by many investi- 

 gators, few have studied in detail the physical 

 and pathological syndromes of damaging but 

 non-lethal exposures to radiation. 



Retardation in the rate of growth of snails ex- 

 posed to radiation has been reported by Bon- 



TABLE 3 Relative Sensitivity of Different 



Embryonic Stages of Trout to 



X-Irradiation 1 



Median eflfective does (LD50) 



Stage irradiated At hatching 



One-cell 78.3 r it 4.42 



Thirty-two cell.. 468 r ± 19-4 



Early germ ring . . 524 r ±: 22.1 



Late germ ring. . 735 r ± 24.7 



Early eye — 



Late eye — 



1 After Welander (1954). 



2S_. 



