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Eggs collected from adult Japanese Medaka were incubated for 16 days in solutions containing 10, 15, 20, and 30 ppb mercury as mercuric chloride. The mean hatchability of control eggs was 46.7 percent. Experimental eggs incubated in 10 ppb and 15 ppb mercury had hatching percentages of 58.3 and 20.8 respectively (Chi Square = 12.8, Pless than.0005). None of the 20 ppb or 30 ppb experimental eggs hatched. Nemorrhaging, blood vessel deterioration and loss of blood cells were observed in 79 percent of the 15 ppb experimental eggs and all the 20 and 30 ppb experimental eggs. Neither the control nor the 10 ppb experimental eggs demonstrated any of these abnormalities. The LC100 for 384 hours was between 20 ppb and 30 ppb. The 10, 15, 20 and 30 ppb experimental eggs concentrated mercury directly from the incubating solution 1,600, 1,900, 2,700, and 1,900 times, respectively. The total concentration of mercury in these eggs after 16 consecutive days was 16,000, 29,000, 54,000, and 56,000 respectively.

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We found selenium dixoide an effective antagonist to the toxic effects of mercuric chloride in the northern creek chub (Semotilus atromaculatus). Selenium pretreatment increased the whole body accumulation of mercury at lower environmental Hg concentrations. It decreased mercury accumulation in survivors at higher, acutely toxic concentrations.

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