| In this paper, F1 and F2 hybrids of Carassius auratus L. Red (♀) X Cyprinus carpio L Yuanjiang ( ♂ ) were studied by means of a series of cellular biological techniques including paraffin section, scanning electron microscope, transmission electron microscope, flow cytometry and karyotype analysis. The structure of gonad of F1 hybrids, especially the ultrastructures of their testis and sperm were investigated deeply, along with the chromosomes of gonad cells of the male individuals and the ploidy of F1 and F2 hybrids. The main results and conclusions were as follows:By the method of paraffin section, three types of gonads were observed in F1 hybrids of Carassius auratus L. Red (♀) X Cyprinus carpio L. Yuanjiang (♂), which were differentiated as testis, ovary and fat tissue with the proportions of 49.6%, 45.6% and 4.8 % respectively. 90.3 % of the testis were partially developed, for the spermatoblasts only partially form spermatozoa. And 3. 24% of the testis were completely fertile, since the entire course of development (from spermatogonia to spermatozoa) could be completed endogenously under pond environment. Another 6.46% of the testis were sterile which could not produce mature spermatozoa. 33. 3% of the ovary were completely fertile and the others consisted of some undeveloped cells and a few of growing oocytes as well as enlarged and degenerated oocytes, which made them ambisexuality. In the fat tissue, there were only two strips of fat tissue located on the gonadal places, and neither testis nor ovary could be observed.In the spermagonia of one-year-old diploid F1 hybrids of Carassius auratus L. Red (♀) X Cyprinus carpio L. Yuanjiang ( ♂ ), only the chromosomes in the metaphase of mitosis were observed in all slides, no bivalent chromosome being found, suggestingthat the spermagonia in one-year old F, were not mature enough to meiosis I . The presence of the chromosome spreads with 100, 200, 390 and 778 chromosomes observed in the metaphase indicated that the diploid F, had the potential ability to generate diploid spermatozoa with the probable mechanism of pre-meiotic endoreduplication.The ultrastructure of testis of Fi hybrids was observed by use of transmission electron microscope. A few of Fi hybrids could produce normal spermatozoa and the process of spermatogenesis was complete. While most of them, the spermatogenic cells, were abnormal and characterized by the condensation of nuclear material and unequal separation of chromosomes.The normal mature spermatozoon was composed of round head, short mid-piece and tail. There was no acrosome at the anterior end of the nucleus, instead there was a vesicle there. The type of "9+2" arrangement was found in the flagellum and there were some vesicles around the flagellum. Several abnormal developed sperms, such as sperm with two nucleus and sperm with two tails, were found in the semen of Fi hybrids. The results of scanning electron microscope revealed that there existed polymorphism in the sperm of Fi hybrids and different sizes of the head of the sperm including haploid, diploid, tetraploid and aneuploid sperm were observed. Similar to the males of F! hybrids, the females were able to produce eggs with different sizes including haploid, diploid and aneuploid eggs.By the use of flow cytometry, the DNA content of Fi and F2 hybrids of Carassius auratus L. Red (■$?) XCyprinus carpio L. Yuanjiang (&) were obtained. Based on these results, a conclusion could be drawn that the Fi hybrids were allodiploid and some of F2 hybrids were allodiploid, while the other F2 hybrids were allotriploid. The chromosome number and karyotype of Fi, F2 hybrids were examined by means of the kidney cell-PHA culture.
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