Reproductive biology of the introduced red-swamp crayfish Procambarus clarkii (Girard, 1852) (Decapoda: Astacidea: Cambaridae) in western Japan

The red swamp crayfish Procambarus clarkii () has been responsible for negative impacts on native benthic fauna and flora in invaded freshwater ecosystems around the world, including Japan. We need to clarify the reproductive biology in the invaded habitats as basic information to effectively control the introduced populations, but the reproductive biology of P. clarkii in Japan (especially in western Japan) has not been well studied. We conducted monthly samplings of P. clarkii from November 2015 to November 2016 in a pond (which does not freeze, even in winter) in Okayama, western Japan, both by using shrimp cage traps and by hand nets to examine aspects of the reproduction, including a form alternation (i.e., Form I and II). We also reared spawning females in the laboratory and calculated the accumulated water temperature during the period to Stage-3 juveniles after spawning. The total number of individuals caught throughout the study period was 6,319 (2,601 males and 2,777 females, with eight of unknown sex and 933 juveniles). The males were all Form I with a breeding status from September to November 2016. We first found ovigerous females in July 2016 and females carrying hatchlings in October 2016, even in January 2016. The form alternation in males was confirmed not only in the cheliped length, but in the hook length. In laboratory observations, approximately 52 days with approximately 1,222 degrees C degree-days of the accumulated water temperature were necessary to Stage-3 juveniles after spawning. Our results indicate that P. clarkii can reproduce within approximately five months of hatching.