The spawning season of Haliotis discus discus along the coast of Kunda, Miyazu City, Kyoto Prefecture

Female Haliotis discus discus, caught along the coast of Kunda, Miyazu City, Kyoto Prefecture (Japan) in September 2009 through December 2010, were checked for their gonadosomatic index (GI) and examined histologically, to estimate the spawning season of this species. According to the results of the histological observation, the shellfish at the spawning stage were appeared between early October and mid-December in 2009 and between mid-October and early December in 2010, with the percentage of shellfish at the spawning stage reaching 100% in November each year. The shellfish at the spent stage were seen in December each year. These results suggest that the spawning season of H. discus discus is October through December, with a peak reached around November. The seawater temperature at the peak of spawning season was 17-20 degree C. It seems difficult to estimate the spawning season of H. discus discus solely on the basis of changes in GI.