Abstract
The spawning possibility of Corbicula japonica in southwest part (lower salinity) of Lake Ogawara was examined by comparing the seasonal changes in maturity, condition index and oocyte diameter between northeast (higher salinity) and southwest part based on specimens monthly collected from August 2004 to September 2005. Judging from histological section on the gonads in northeast and southwest part, the spawning occurred in early July to early September. Furthermore, condition index and oocyte diameter both in northeast and southwest part were maximal value in those months and then, decreased in late September. The artificial spawning induction experiments were performed to know the minimum level of salinity and range of the temperature for spawning and survival of the larvae. Samples were exposed to water temperatures 29.0, 27.0, 25.0, 23.0, 21.0°C and salinities 4.0, 2.0, 1.5, 1.2, 1.0, 0.5, 0.0 psu. Spawning and normal development of larvae were observed at 1.0 psu and 29.°C. These results suggested that C. japonica in southwest part of the lake with low salinity may spawn the eggs, and the development normally occurred when salinity and water temperature could maintain more than 1.0 psu and 29.0°C.
