Comparison of maturity based on collection period to develop broodstock management technology
Jongcheol Han, Injun Hwang, Jungha Kang and Heewoong Kang
West Sea Fisheries Research Institute, NIFS, 14, Seonnyeobawi-ro, Jung-gu, Incheon, Korea

Ark shell, Scapharca subcrenata were collected at different harvest period to induce sexual maturation. The gonad index varied according to when the first entry, ranging from 1.15 in January to 1.34 in February and 1.84 in April. It was observed that the gonadal index increased as the season progressed, with higher values recorded in later months. When water temperature stimulation was used to induce sexual maturity, the time to maturity was 123 days in January, 89 days in February and 53 days in April. The accumulated water temperature was 944°C in January, 812°C in February and 780°C in April, giving a total difference in accumulated water temperature between January and April of T = 164°C. Analysis of the gonadal tissues at the end of the experiment showed that the female/male ratio and the frequency of immature individuals varied according to the collection season. In January the female-to-male ratio was 63.3%, in February 40.0% and in April 36.7%. Similarly, the proportion of immature individuals was 3.3% in January, 16.7% in February and 20.0% in April. A total of 600 ark shells were used for artificial seed production on June 8th. The fertilization rate was approximately 89%, and the hatching rate was 90%. In total, 3.04 billion fertilized eggs were collected, resulting in 1.1 billion hatching. The initial D-shape larvae measured 80.4 ± 3.9 μm in length and 60.6 ± 2.8 μm in width.

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