FISHERIES RESEARCH INSTITUTE,MOA,TAIWAN

The study was aimed to develop improved methods for spat attachment on various substrata. Using oyster shell as substrata, the settling rate was about 30% among groups with larvae to shell ratio between 40 and 100. More larvae settled on the oyster shell as ratio of larvae to shell increased. Larvae settled on the oyster shell in the middle position of the oyster string were more than those in the upper and lower position. More larvae settled on the outer surface of oyster shell in the middle position of the oyster string. Shell granule sizes (250~530，500~1000 and 1000~1500 µm) had no effect on the settling rate. The settling rates were affected by the ratio of larvae to the number of granules. The setting on the larval shell ratio 1:2 was the highest, 2:1 was the lowest and 1:1 was in between. Besides, more larvae settled on the oyster granules as the bottom surface of container increased. High settling rate (42%) occurred if the plastic plates were immersed in pond water to allow microbes grew on the surface. Settling rates decreased dramatically as the microbes on the surface of plastic sheet were removed with water flow (28％), or scratched with plastic or steel brushes (4% and 2%, respectively). The results indicated that the microbes grew on the surface of plastic sheet enhanced the settlement of oyster eyed larvae. From three temperature remote settling experiments, settling rates of eyed-larvae after being stored in 4 ℃ were the highest, the lowest in 12 ℃, and 8 ℃ in between. The settling rates of eye-larvae after being stored at 4 ℃ from 1 to 4 days were 20, 16, 8, and 3%, respectively.