Artificial breeding, early growth and development of Panopea japonica

The geoduck clam Panopea japonica is of high commercial potential. Currently, its sales in China account for over 90% of its global sales and all the geoduck clams sold in the Chinese market are imported from Sea of Japan. However, artificial breeding of P. japonica on a large scale is rarely reported. This study for the first time tried artificial breeding of the geoduck clam P. japonica in an indoor hatchery in spring and autumn. Growth and development of the artificially bred P. japonica in the two different seasons were compared as well. The results showed that for the parental P. japonica, the reproduction peak period was observed in May and October, with a single spawning amount of (3×10⁶) - (5×10⁶) eggs/female and an egg diameter of 75-85 m. In spring, when the water temperature was raised to 18.6-19.0℃, the lowest growth rate was observed in 6-9 days old and 15-18 days old individuals, with a daily growth rate of shell length at 1-3 μm/day. For the larvae at other growth stages, average growth rate of shell length was 9-15 μm/day. After 30-40 days’ cultivation, P. japonica developed into the juvenile stage and the average shell length reached (4.94±0.93) mm. For juveniles, the average growth rate of shell length was 50-167 μm/day. In spring, average production was 2 695 spat/m³. Fertilization rate, hatching rate, larval survival rate, metamorphosis rate and juvenile survival rate of P. japonica artificially cultivated in spring were 89.60%±3.21%, 38.60%±3.77%, 13.40%±1.52%, 29.80%±4.82% and 40.60%±1.74%, respectively. In autumn, the water temperature was from 17.4 ℃ to 13.2 ℃. Growth and development of larval P. japonica were relatively slow and after 148 days’ cultivation, average shell length of the juveniles reached (2.88±0.47) mm and average production was 6 666 spats/m³. Fertilization rate, hatching rate, larval survival rate, metamorphosis rate and juvenile survival rate of P. japonica artificially cultivated in autumn were 95.20%±1.92%, 14.60%±2.41%, 70.60%±5.46%, 59.20%±3.35% and 70.40%±2.30%, respectively. Then the spat was transferred to outside pool for further cultivation, which could eventually reach (13.22±2.39) mm. In comparing the growth and development of the artificially bred P. japonica in spring and autumn in Northern China, large size seeds suitable for bottom sowing could be produced in autumn at a relatively low cost. This study has provided a scientific basis for larval breeding, high-efficient cultivation and resource restoration of P. japonica in China.