室内飼育におけるクロダカワニナの成長と産仔数 Growth and Number of Newborns in Semisulcospira kurodai (Prosobranchia : Pleuroceridae) Reared in the Laboratory
Growth and number of newborns in Semisulcospira kurodai reared during 48-52 months under the laboratory conditions were studied. The newborns, which were produced in July 1988 and August 1989, grew up to 10.3mm in mean shell diameter by the age of 1, 11.0mm by the age of 2, 11.5-11.8mm by the age of 3, and 12.0mm by the age of 4. The maximum size of S. kurodai is 13.3mm in shell diameter, 52.0mm in shell height, 7.7g in wet weight with shell at the age of 4. The production of newborns has begun in snails grown up over 9mm in mean shell diameter at the 8-10th months after the birth. Birth of newborns occurred at a water temperature between 12℃ and 24℃. Large number of newborns were produced at a water temperature over 20℃. Number of newborns produced during a month per female is estimated 10-20 individuals at water temperature between 20℃ and 24℃. Large number of newborns during a year were produced by mature females larger than 10mm in mean shell diameter at 1-3 ages. Mean number of newborns produced during a year per female at 1-3 ages is estimated 62-79 individuals.