A natural habitat of the freshwater crayfish Cambaroides japonicus (De Haan, 1841) in Odate City, Akita Prefecture, Japan is designated as a natural monument by the Japanese government. Change of egg color of C. japonicus with
the development of their eggs were observed in aquaria in Oga Aquarium GAO in Akita Prefecture, Japan. The egg color was dark brown immediately after spawning, then the color changed to black, and eyed eggs appeared before egg hatching.
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