Annual reproductive cycle of the threatened cyprinid species, Pseudorasbora pumila subsp. sensu Nakamura (1963)

Abstract

In order to clarify the reproductive cycle of on the threatened cyprinid species, Pseudorasbora pumila subsp. sensu Nakamura (1963), histological observations were conducted on gonads of male and female specimens collected from Inuyama City, Aichi Prefecture, Japan. The maturation process was divided into two phases. In the first phase, from September to December, primary spermatocyte formation in males and cortical alveoli formation followed by accumulation of yolk globules in the oocytes in females were observed. Concurrently, gonadosomatic indices (GSI) increased gradually during the first phase. The second phase, from March to April, was accompanied by rapid increases in GSI. Active spermatogenesis (second meiotic stage) in males and active accumulation of yolk globules in the oocytes in females also occurred during the second phase. The spawning period is probably from April to June. Multiple spawning during a single spawning season in this subspecies was indicated in the histological observations of ovaries. Moreover, changes in water temperature were probably significant factors in the onset and the cessation of spawning as in other cyprinid fishes. The spawning period of this subspecies was very similar to that of P. parva, raising the question of competition for spawning territories or substrate between the two species.