An experiment was conducted to investigate the annual reproductive cycle of a Korean endemic species, Acheilognathus majusculus, from Jeokseong-myeon located in Seomjin River. The reproductive cycle is examined histologically regarding water temperature and day length of the habitat, the gonadosomatic index (GSI), the female ovipositor length index (OLI), monthly variation in egg diameter distribution, and developmental characteristics of female and male gonads. The maximum GSI was found in 19.21±2.32 and 6.90±0.53 for female and male respectively when water temperature (14℃) and day length (11.1hr) began to rise. On the other hand, the minimum level was reached during August (1.87±0.67 for female and 0.88±0.50 for male). No samples represent with measurable ovipositor between September and November, while the longest ovipositor length index was in April (79.68±4.69%). We compared and calculated the stages of testis and ovary development process in order to determine the germ cell development characteristics and the reproductive cycle. According to the result, we classified the female Acheilognathus majusculus reproductive cycle into four stages: Ripe (April) and spawning phase (May to June), degenerative phase (July), growing phase (August to December), and mature phase (January to March). The annual reproductive cycle of male Acheilognathus majusculus was categorized into five stages viz. Ripe and spawning phase (May to June), degenerative phase (July to August), resting phase (September to November), growing phase (December to February), and mature phase (March to April).
Keywords: Acheilognathus majusculus; Gonadosomatic index(GSI); Reproductive cycle; Spawning.