Using tissue culture technique, we have succesfully established two cell lines from caudal fin of red carp (Cyprinus carpio red variety) and crucian carp (Carassius auratus gibelio), a kind of fish with natural gynogenesis. In TC-199 medium supplemented with 15% calf serum, the cell line of crucian carp, named CAG-87, has been proliferating vigorously through 90 subcultures over a period of 18 month. At the optium gnwth temperature of 27 ℃ and PH value of 6.8, monolayer can be formed about 3-5 days with incubated concentration of 1.2 * 10~4 cells per ml. Twenty-four hours plating, the highest index of mitotic division of cells reaches up to 44%. The precentage of cell with 156 chromosome in 22th passage is 45% and the distribution of chromosome number is ranged from 130-164, so it is heteroploid cell hine. The best growth of red carp cell line requires PH value of 6.8, TC-199 suplemented with 20% calf serum and incubation temperature of 27 ℃. The highest index of mitotci division is 39‰. The precentage of cell with 100 chromosome in 24th passage is 90%. After 85 subcultures over a period of 17 month, the line is named CCRV-87. Using CCRV-87, CAG-87 and CAB-80, a former established fish cell line, we studied some problems about microcells and minisegregant cells (a cluster of small cells which looks like bunches of grapes) such as preparatcon of fish microcells, minisegregant cells and the mechanism of their formation. In the preparation of their formation. In the preparation of mcirocells, the pncedure of micronucleation in fish cells was observed, it showed that the formation of micronuclei was the result from abromal division of interphase nuclei. We also studied the effects of concentration and treatment time of colcemid on three fish cells so that the micromucleation in CAB-80 reaches up 60%, CCRV-87 and CAG-87 reach up 30%. It is harmful to treat fish cells with high concentration or prolonged time of colcemid. The main procedures which can yield large q quantity of fish minisegregant cells are described as follows: 16 to 20 hours after incubation, colcemid is added to cell cultures of CAB-80 at the final concetration of 0.3 ug/ml. Mitotic cells are obtained by continuing in incubation for another 10 to 14 hours. Then the mitotic blocked cells are harvested and stored at 4 ℃ for 10 hours. Mang cells disply highly a bromal pattern of division at PH 8.0 and about 50% of them form minisegregant cells. Analysis of genetic material distribution and observation of electron micronscopy show that during the process of minissegregant cell formattion, the change of nucleu is the same as cell micronueleation, but the cytokinesis are severely disturbed. Micronuclei can be sepreated into m many daughter cells, by irregular cleavage of cytoplasm. In order to explore new route in fish breeding via reconstitution between minisegregant cells and fish fertilized eggs, we introduce the technique of minisegregant cell-mediated chromosome transfer to fish cells and fuse minisegregant cell with fish fertilized eggs. Although minisegregant cells can be fused to fish fertilized eggs with PEG, the fused micronucleis are mantained interphase nuclei and not fused with nuclei of eggs.