Some effects of acute ⁶⁰Co gamma radiation on four developmental stages of the brine shrimp, Artemia salina (L.)

Abstract

Special developmental stages of Artemia salina (L). were exposed to graded doses of gamma radiation, ranging from 0 to 200 KR, and maintained in a seawater culture medium containing 5% NaCl. Light was kept constant at 200 ± 10 foot candles and temperature maintained at 26° ± 2°. The hatchability of the cyst (blastula) stage was not affected when irradiated, after soaking in seawater, with doses of up to 75 KR. Reduction in hatch ability of wet cysts treated at the 100 KR level was doubtfully significant (P <0.1). An explanation, based on the relative activity of the nuclei and the extent of their dispersion within the cyst, was offered to explain the extreme radioresistance of partially hydrated cysts. Reduction in total length of larvae hatched from irradiated cysts was found to be significant at the 1% level and linear with dose. Differences in the group means of width/length ratios of larvae treated in stage 0 at dose levels of up to 20 KR were significant and linear with dose. The threshold value for eye abnormalities in larvae irradiated in the cyst stage was found to be between 25 and 50 KR. Eye defects occurred at most dose levels up to 100 KR in larvae treated in stage 0. Development of genitalia was not affected in larvae irradiated with dose s up to 100 KR, at a time coincident with the appearance of the genital anlage. Lethal dose survival curves for larvae irradiated in the cyst stage and in stage 0 were sigmoidal. Cumulative mortality curves for stage 12 shrimp exposed to dose levels between 25 and 100 KR, and stage 19 (adult) shrimp exposed to dose levels of 25 to 200 KR were sigmoidal at the lower dose levels, approaching linear at the highest levels. The threshold-lethal dose for all larvae treated at stage 0 was found to be between 10 and 15 KR. Adult males showed a greater radioresistance at the higher dose levels than adult females. Changes in radiosensitivity were most drastic between 175 and 180 KR for males and between 160 and 175 KR for females. The LD₅₀ 1-day doses were found to be 180 KR for adult males and 175 KR for adult females. Of the four developmental stages treated, stage 19 was most resistant to radiation. Stage 0 was least resistant. LD₅₀ and LD₁₀₀ doses for various time periods were tabulated for the four developmental stages treated. Mitotic activity in the blood-cell-forming organs of adults was arrested by doses of 100 to 175 KR, preventing replacement of cells contributed to the blood stream. Reduction in size of the blood-cell forming organs of shrimp treated at these dose levels was found to be highly significant as compared to controls, P <0.001. Animals treated at 200 KR died before measurable reduction of these organs occurred. Mating, activity declined in direct proportion to dose level. Dose rates of up to 100 KR apparently had no effect on the molting rate of stage 0 larvae. Approximately 1 molt/day was recorded for each larva for up to 7 days or until death of the individual. Presumably radiation damage to the experimental animals was accomplished through the mechanism of direct hits on mitotically active nuclei, e.g., mesoderm cells, and on the interphase nuclei of the phagocytic storage cells. Radical formation was believed to have caused metabolic imbalance resulting in death, particularly in adults.