Tetraploidized cell strains of grass carp (Ctenopharyngodon idellus) and tetraploid gastrula of loach (Paramisgurnus dabryanus and Misgurnus anguillicaudatus) are obtained from the cultured kidney cell line of grass carp (GCK-84), the blastula cells fused with the unfertilized eggs of loachs using the techniques of electric fusion and polarized injection. 1. The most optimum conditions of the electric fusion of GCK-84 cell line are explored with orthogonal test. The density of cells is 4.2 * 10~5/ml. Cells treated with pronase E(40 ug/ml) for 10 minutes at the temperature 25 ℃. The fusion medium consists of 0.2M mannitol and 8 * 10~(-6)M CaCl_2. Then, the percentage of dikaryon may reach 40.13% on average. Among the above factors, the density of cells is the most important to the percentage of dikaryon, and the next, the concentration of Ca~(2+). The concentration of mannitol is the most unimportant. The most optimum conditions of the fusion of the loach blastula cells are as fallows: The density of cells is 2.5 * 10~4/ml. The temperature is 18 ℃ and the fusion medium consists of 0.2M mannitol and 8 * 10~(-5)M CaCl_2. Then, the percentage or diraryonmay reach 50.99% on average. Among the above tractors, the concentration of mannitol is the most important to the experiment results and the comeootration of Ca~(2+) is the most unimportant. 2. After the blastula cells of loachs was treated with electric fusion, the nuclearfusion rate of dikaryon is increased and the survival rate of the cells is decreased with the passage of time. 3. After the fused nuclei were injected into the unfertilized eggs with the method of polarized injection, 88% eggs can normally develop to blastula stage. Then, 37.13% blastula can reach gastrula stage. Few and far between gastrula can become fry. Chromosome number of the above blastula and gastrula is inspected and 28% is tetraplont. The number of chromosome ineach cell is 90-96. 4. The caudal fin cells of the fish, which were from the unfertilized eggs injected with diploid blastula cell nuclei of loach, were examined. The number of more than 71% metaphase chromosome is the number of diploid chromosome as the same as the donor cell nuclei. 5. In sterility, fused GCK-84 cells were cultured clonally. Six tetraploidized clonal strains were sieved from 54 clones. The numbers of their chromosomes are 96, 100, 108, 116, 124. At present, they have been subcultured to the ninth passages. The successful sieving of tetraploidized cell strain offers another method to induce tetraploid cell strain artificially. And it will also open a new way for inducing tetraploid fish artificially.