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Three genes p53, rarα1, wnt and liver of Medaka fish tissue were selected to study the toxicity of DDT to fish embryo (8 days old) and adult Medaka fish (3 months old). TEM and real-time PCR methods were used to examine changes in structure of liver tissue and genetic expression. The TEM results recorded a clear difference between the control and the experimental sample. Adult Medaka fish exposed to 1µg/L DDT for 24 hours has a distorted liver cell nucleus with many hollow lipid particles, and the sinus-shaped meshes are clustered, interrupted; lysosome is not intact with many degenerative bubbles. The results of real-time PCR analysis showed that DDT affects the development, different and proliferation of cells in the embryonic stage and gene expression in adult stage. All three genes p53, rarα1 and wnt in fish embryos changed strongly and tended to be inhibited when exposuring with 1700µg/L DDT, the values ​​were recorded respectively 0.9; 4.9 and 5.4 times compared to the control sample (1 times). For adult fish, gene expression was lower than fish embryos with real-time PCR analysis values ​​for the three genes p53, rarα1 and wnt respectively 0.9 and 0.5; 0.36 and 0.09; 0.53 and 0.09 times after exposure to 1500 and 1700 µg/L DDT. These results demonstrated that gene expression is dependent on the developmental stage of the cell as well as on the dose of the chemical exposed. The development, cell differentiation/proliferation in the embryonic and adulthood stages affected differently to the cell gene expression.

The one-day-old O. latipes embryos is harvested and exposed to different concentrations of o, p`-DDT 0.04; 0.08; 0.12; 0.16; 0.2; 0.24; 0.28 and 0 µg/l (the control sample is not supplemented with o, p`-DDT) for 24, 48, 72 and 96 hours. After 24, 48, 72 and 96 hours, the results showed that LC50 value is gradually decreased, respectively 0.1013; 0.0772; 0.0486 and 0.0359 µg/l. The difference between LC50 values depends on the exposure concentration and exposure time. The results showed that the mortality rates of Medaka O. latipes increased with increasing pesticide concentrations as well as increasing exposure time. The experiment for observation of morphology and structure also found malformations in the spine and eyes of fish embryos. This chemical has strongly affected embryonic heart rate and embryonic morphology during growth and development.

The purpose of this study was to evaluate the acute toxicity of pesticides including DDT, endosulfan, lindane and atrazine to Medaka Oryzias latipes fish embryos by identify the LC50 value and ratio of mortality after 24, 48, 72, and 96 hours of exposure. The fish O. latipes was obtained from the Biotechnology Center of Ho Chi Minh City, Vietnam, raised, and allowed sexual fertilization to conduct embryo collection. The one-day old fish embryos is harvested and exposed to different concentrations of DDT, endosulfan, lindane and atrazine respectively: 1,300; 1,500; 1,700; 1,900; 2,100 and 2,300 µg.L-1 DDT; 0.01; 0.1; 1 and 10 µg.L-1 endosulfan; 0; 80; 110; 130; 150; 170; 210; 250, and 300 µg.L-1 lindane and 150; 250; 350, and 450 µg.L-1 atrazine. The results showed that endosulfan had the highest toxicity in the four surveying groups, starting at concentration of <1 μg.L-1 (0.6 μg.L-1). The study also noted that four kinds of pesticides caused serious effects on fish embryo growth and survival. Their toxicity gradually decreased from endosulfan to lindane, atrazine and eventually DDT with LC50 values after 96 hours of exposure were 1123.8; 0.6; 116.2 and 165.2 μg.L-1, respectively. The differences between the LC50 values depended on several factors, such as the toxicant concentration, the exposure time... The mortality rates of Medaka embryo O. latipes linearly increased with the toxicant concentrations and the exposure duration. These pesticides inhibited growth leading to the fish embryo death.