Black-lipped pearl oyster (Pinctada margaritifera) spat were produced in the hatchery of the College of Micronesia (COM) at Nett Point, Pohnpei. Forty-four days after fertilization, the spat, which had settled on “tank spat collectors,” were transferred to specially constructed grow-out farms by COM.

The spat were placed in protective mesh nets with a 0.75 × 1.5 mm mesh size, suspended at a depth of 2–3 meters. After two months of grow-out, they were distributed into 48-pocket panels (4 mm square mesh), then graded and transferred into panels with larger mesh or lantern nets as they grew (at 4, 6, and 9 months).

Growth Results

Mean growth measurements (± standard deviation), based on anteroposterior length (APL) and dorsoventral height (DVH), were as follows:

• 6th month: 38.0 mm ± 7.1 (APL) and 39.8 mm ± 6.4 (DVH) (n = 206)
• 9th month: 57.4 mm ± 6.2 (APL) and 55.5 mm ± 7.1 (DVH) (n = 87)
• 12th month: 81.9 mm ± 8.1 (APL) and 83.9 mm ± 7.6 (DVH) (n = 118)

These values are comparable to those obtained in northeastern Australia by Southgate and Beer (1997) and higher than those reported by Southgate and Beer (2000) for juveniles aged 7 to 12 months (max. DVH 65.8 mm), confirming faster growth in Pohnpei. The maximum recorded DVH reached 97.6 mm.

High Survival and Consistent Results

Survival rates between 4 and 12 months, and between 6 and 12 months, were 83.2% and 91.3%, respectively. Over the course of 2002, successive trials showed remarkable consistency, with survival rates ranging from 88.9% to 98.5% depending on the monitoring phase.

The mean DVH/APL ratios of the first two hatchery-produced batches in 2002 were 1.035 (± 0.050; n = 118) and 1.042 (± 0.085; n = 139), with no significant difference (P > 0.05), confirming the uniformity of the individuals produced.

Outlook for Pearl Production

These results confirm that the grow-out method implemented in Pohnpei is effective and that the local environment is particularly favorable for the development of hatchery-produced pearl oysters.

Nucleus implantation is scheduled to begin in September 2003 to test the quality of black pearls produced from both hatchery and wild-collected oysters.