2010 Volume 64 Issue 1 Pages 39-43
This paper describes the examination results for clarifying the first maturation and season of hanging cultured iwagaki oyster Crassostrea nippona in Uragou Bay, Oki, Shimane, Japan. 0-year old oysters were collected monthly from May to December in 1995, and shell height, soft tissue weight, gonad index and standard histological analysis were measured to observe the stages of gametogenic development and spawning. From the results, it was clear that the season for starting early gametogenic development of 0-year-old oysters was later than that of fishery size oysters in published reports. Most of the oysters were mature in August, with a mean shell length of 50mm. It was estimated that the spawning peak occurred between August and September, coinciding with a decrease in water temperature from the highest temperature, which is the same season for fishery size oysters