Fecundity of the Japanese crayfish, Cambaroides japonicus: ovary formation, egg number and egg size

Ovary formation, egg number and egg size was studied to examine the fecundity of the Japanese crayfish Cambaroides japonicus. From histological observations of ovaries, the ovarian eggs of C. japonicus developed as asynchronous oocytes. Many well-grown oocytes were in the ovary after spawning, as well as before spawning. The smallest carapace length of ovigerous females was 15.2 mm. The pleopodal egg number ranged from 22 to 75 and significantly increased with female body size. Both egg diameters (2.13–2.50 mm) and weights (0.009–0.017 g) also significantly increased as the female body size increased, but were variable even for the same size crayfish. We conclude that larger females should be used for seed production of C. japonicus because of its high fecundity and large eggs. Mature females spawn only once a year in natural habitats, but multiple spawning can be artificially induced within 1 year because of well-grown oocytes that remain in the ovary after spawning. Thus, we recommend that an effective technique for artificial induction of multiple spawning be developed from our results.