The Reproductive Cycle Of Branchiostoma Belcheri And B. Japonicum In Xiamen Waters

The amphioxus or lancelets are basal chordates, they played an important role in studying the evolution of vertebrates. The amphioxus species were widely distributed all over the world. The lancelets, mainly distributed in Xiamen, Qingdao and other coastal areas, have been enlisted as second grade national protected animals in China. It is meaningful that they could provide a basic theory in artificial culture and modeling lancelet program. Since the scientists identified taxonomically the lancelets in Xiamen waters as Branchiostoma belcheri, the report about reproductive cycle of the lancelets are quite inconsistent. In recent years, some researches made conclusion that there are two amphioxus species(Branchiostoma belcheri and B. japonicum) in Xiamen waters. The present study focused on the gonadal development cycle and breeding season of the two lancelets. The isozyme spectra were also compared among three lancelets B. belcheri, B. japonicum and B. floridae.Through the appearance and histological observation on gonadal, the whole cycle of gonadal development was divided into seven stages:Undeveloped, stage Ⅰ, Ⅱ, Ⅲ, Ⅳ, V and Post-spawning period. In Xiamen waters, B. belcheri began to develop their gonad in late April, and matured in June, the first spawning period occurred in late June. After spawning, the gonad of B. belcheri developed again from July to September and the second spawning period occurred in late September. Then the gonad degenerated gradually from October to early April next year. The B. belcheri have two breeding seasons with a short interval through a year. The B. japonicum has two distinct breeding season. In the first breeding season, the B. japonicum begin to develop gonad in late November, then matured and spawned in April next year. In the second breeding season, the B. japonicum developed their gonad from June to September, and the spawning peak occurred in September. In conclusion, the breeding period from July to September were overlapping between B. belcheri and B. japonicum.When comparing the phenotype of the five kinds of isozymes (MDH, SOD, EST, a-AMY, ADH) among three lancelets by a vertical flat-bed discontinuous polyacrylamide gel electrophoresis technique, we have got five effective results, found that there were significant differences in the number, staining intensity and relative mobility of enzyme spectrum among three lancelets, and the difference of gonad leads to differences expression of the isoenzymes.