G¨¹nther Light Microscopic Observation Of Embryonic Development And Karyotype Study

The fertilized eggs of Cynoglossus semilaevis Gunther were observed under the anatomical microscope in different developmental stages. And the karyotype of Cynoglossus semilaevis Gtlnther was studied.The mature parent fish of Cynoglossus semilaevis Gunther was artificially induced to spawn eggs. The incubating conditions are, the water temperature changed between 20.4 ℃ and 21.6℃, the salinity is 35‰, and PH retained in the range of 7.8 and 8.6. The fertilized eggs were observed under the anatomical microscope in different time to record the developmental stages and to describe the morphological changes. According to the experiment, the protoplasm centralized to the creatural pole, and the oil globules distributed to the plant pole after the fertilization. The egg belongs to typical telolecithal egg and discoidal cleavage. The first cleavage could be seen in 1h30min. The fertilized egg entered the 4-cell stage in 2hlOmin, and the 8-cell stage in 2h20min. The fertilized egg entered the 32-cell stage in 3hl2min, and the cells distributed in different layers. The fertilized egg entered the multi-cell stage in 4h05min and the early blastula stage in 5h. It enter the late blastula stage in 6h50min. The fertilized egg entered the early gastrula stage in 11h45min, the germ ring appeared, and the oil globules diffused in the plant hemisphere in this stage. The embryonic shield appeared in 15h, and the fertilized egg entered the middle gastrula stage. Some brown chromatophores appeared in about 18h. The blastopore closed in 22h20min. The tail-bud formed in 24h20min, the heart could be seen at the same time. Embryo almost encircled the yolk-sac in 38h40min. The larva broke out of the egg in 39h50min, at that time, the number of the oil globules decreased greatly. The whole incubation needs about 40 hours.The accumulated temperature of each stage of Cynoglossus semilaevis Gu nther was calculated with the record of the time and the temperature according to the principle of accumulated temperature. The summation of all the accumulated temperature was necessary with which the fertilized egg could get through its development of the embryo stage. The summation was 837.92(hour* ℃),and the average temperature was calculated to be 21.0℃ according to the summation and the total time.Larval fish of Cynoglossus semilaevis G unther were treated with colchicines to get the karyotype , 12~50-day larval fish were selected to be putinto the solution of colchicine of different concentration for 5-6 hours. The fin, and the other part of the fish were cut off to be treated with low concentration infiltration, solidify, eduction and other procedures. At last, the suspending cells can be gained and treated with air-drying method. The specimens were dyed with Giemsa. The metaphases of mitosis were observed under the microscope and the well-dispersed metaphases were selected to statistic the number of the chromosomes. The good-formed metaphases were used to be microphotographed, magnified and measured to study the karyotype of Cynoglossus semilaevis Gu nther. The chromosomes were sorted according to Levan's standard. The best tissue was the fin. The concentration of colchicines had great effect on the configuration of the chromosomes, and the concentration of 0.02% is better. The concentration of the KC1 affected the crash of the cells, and had indirect effect on the dispersion of the metaphases. The concentration of 0.0375% is better than that of 0.075%.The conclusion can be drawn according to the observation of 517 clear metaphases of mitosis that the number of diploid chromosome is 2n=42 and the karyotype formula is 42t, NF=42.A special huge chromosome was observed in a part of larval fish. The proportion of individuals that has the special chromosome was equal to the proportion of individuals that has not. The special huge chromosome is concluded to be sex chromosome.