Process of gametogenesis in golden venus chub, Hemigrammocypris neglecta (Cyprinidae), with special regard to the comparison in initiation pattern of gametogenesis with other cyprinids

Most cyprinid fish breed from spring to summer. On the other hand, the timing of initiation and duration of gametogenesis in preparation for reproduction vary widely depending on the species. It is unclear what factors determine the types of timing and duration of gametogenesis. In order to infer the factors, it is necessary to clarify the gametogenesis process of as many species as possible, categorize them, and explore commonalities and differences between species belonging to different types of gametogenesis. In the present study, we determined the maturity of Hemigrammocypris neglecta, a temporary water-spawning fish of the subfamily Oxygastrinae, based on histological observations of the gonads. Female vitellogenesis began in May and continued during the breeding season from May to August. This species was a multiple-spawner that repeatedly ovulates and spawns multiple times during the breeding season. Male spermatogenesis (meiosis) began in April, and a large number of spermatozoa were observed in the testes and sperm duct from May to August, indicating that reproduction is possible during this period. The timing of the initiation of gametogenesis in spring/summer-spawning cyprinid fishes has been roughly divided into three types: autumn type, winter/spring type, and breeding season type. The female H. neglecta was the breeding season type. There are few species that belong to this type, suggesting that the type may have evolved independently with reflect the reproductive ecology of each species. The male is the winter/spring type, a characteristic common to the subfamily Oxygastrinae.