Life history of the freshwater shrimp, <i>Palaemon paucidens</i>, in the Nishimoune River, Kesennuma, Japan

Abstract

The life history of Palaemon paucidens, a common freshwater shrimp inhabits many freshwater areas in Japan, remains unclear. In the present study, we surveyed a single population in a stream in Kesennuma, Miyagi Prefecture, Japan to elucidate the life history of this species. The spatio-temporal distribution pattern of the surveyed population was investigated in samples from seven stations established along the upstream and downstream sections of the stream. Size composition, state of sexual maturation, and appearance of hatched larvae were observed in samples collected from the mouth of the stream. Molecular species identification was used to confirm that the samples were P. paucidens. The results indicated that the total population consisted of three year-classes, and that many of the matured individuals(one or two years old)of both sexes seasonally migrated to the mouth of the stream. However, because some individuals remained in the freshwater area upstream, the migration of this species at our study site was partial. Larvae appeared at the same time as adults migrated downstream, and larvae hatched only at night. Based on age estimations in the field and the spawning intervals of females in a laboratory, it was peculated that two-year-old individuals would die after reproduction while one-year-olds would migrate upstream again. As the seasonal migration of both males and females corresponded to reproduction, we conclude that P. paucidens at our study site show diadromous migration and that their main migration pattern is catadromy.