1927, someone in Japan brought two crayfish from Hawaii and wanted to cultivate them into bait for bullfrogs. However, unexpectedly, crayfish have super vitality and ability to adapt to the environment, which is out of control and is rampant in Japan.
About 1929, crayfish were probably introduced to China as pets or bait. The place where crayfish first landed in China was near Nanjing, which may be one of the reasons for misunderstanding, but it was much earlier than the Nanjing Massacre.