The ultrastructure of gonad in Ganchang hybrid crucian (Carassius cuvierius ♀Cyprinus carpio var. singuonensis ♂)

The anatomical observation and histological section were used to investigate the development of gonad in 126 Ganchang hybrid crucian (Carassius cuvierius ♀Cyprinus carpio var. singuonensis ♂) in reproduction season. The results showed that the development of gonad in Ganchang hybrid crucian was quite unique, in most cases demonstrating one-side or two-side dissymmetric. Three types of gonad structure of Ganchang hybrid crucian were found and observed under light and electron microscope. The first type was free-gonad type (fat tissue type), which accounted for 24.6% of the total. Only two strips of fat tissue located at the gonadal place, neither testis nor ovary was observed. The second type was testis type, which accounted for 46.83%. It consisted of many lobules, where numerous spermatides existed. Most degenerated or abnormal spermatides were found, and only very small number of mature spermatozoons were observed. However, after abdominal compression, semen outflow was always not found, indicating male sterility. The third type was ovary type, which accounted for 28.57%. The gonad consisted of oocytes, which could develop to phase Ⅲ and gradually degraded in phase Ⅳ. Mature egg, ovulation and egg outflow were not observed by dissection and extrusion, showing female sterility. The testis-type gonad and ovary-type gonad were different in ambisexuality, and testis-dominated gonad and ovary-dominated gonad had the ambisexuality proportion of 25.4% and 11.11%, respectively.