Toxicity of cadmium and its accumulation on the egg and larva of Medaka Oryzias latipes.

Toxicity and accumulation of cadmium to the eggs and larvae of medaka Oryzias latipes were examined in cadmium concentrations of 0.1-4.0ppm.The eggs were not adversely affected by the cadmium concentrations of 0.1-2.0ppm , but their hatchability significantly decreased at 4.0 ppm.In the larvae exposed to cadmium concentrations higher than 0.2 ppm, rates of survival decreased, and symptoms of cadmium poisoning such as erratic swimming and loss of equilibrium were observed.The amounts of cadmium accumulated by the eggs reached stable levels for a short period, depending on the cadmium concentrations in test solutions.The accumulation of cadmium by the larvae increased rapidly with exposure time at all concentrations (0.1, 0.4 and 2.0 ppm).The eggs accumulated cadmium as much as 32-280 ng/egg when exposed to cadmium concentrations of 0.1-4.0ppm.On the other hand, the larvae accumulated cadmium 2.6-5.5 ng/larva in the test solutions with cadmium concentrations of 0.1, 0.4 and 2.0 ppm.The eggs could accumulate cadmium 10-30 times higher than the larvae.Thus, the reason that the eggs were more resistant to cadmium than the larvae is thought as follows: most of the cadmium accumulated in the eggs remains on the chorion and is scarcely trans -ferred into the embryos, whereas cadmium accumulated in the larvae is immediately transferred into target organs or tissues. Mckim1)