LARVAL REARING, SETTLEMENT AND EARLY GROWTH OF TROPICAL BLACK-LIP PEARL OYSTER (Pinctada margaritifera, L.) IN CHUUK, FSM

Abstract

The black-lip pearl oyster, Pinctada margaritifera is infrequently occurred on subtidal sand flats along the Chuuk lagoon, Federated State of Micronesia (FSM). P. margaritifera are considered to be one of the most important species in the black pearl industry. Despite their importance, few studies have been conducted on larval rearing and early growth of the oyster in FSM. The present study reports the larval pearl oyster rearing in hatchery and the spat growth at different culture depths (3, 6 and 9 m) from 4 weeks post-settlement to 18 months during the period from May 2002 to October 2003 in long-line hanging culture ground. Broodstock pearl oysters were induced to spawn by increasing water temperature to 30°C followed by rapid decreasing in water temperature. Female oysters spawned a mean of 12×106 eggs. The maximum number of eggs spawned per individual was 24×106. Mean egg diameter was 50.1±2.1 μm (±s.d., n=60) during the spawning. Oyster larvae reared at 28–30°C and fed algal diet including Isochrysis galbana, Chaetoceros simplex, Phaeodactylum triconutum and Pavlova sp., and reached the settlement for 18 days after fertilization. Survival from fertilization to settlement stage was low (0.7%). At 4 weeks post-settlement, spat had a mean shell length of 3.2±0.2 mm and a mean total weight of 2.2±0.9 mg. After 18 months of rearing in different culture depths, spat in 6 m culture depth had highest growth rate with a mean shell length of 8.9±1.1 mm and a mean total weight of 104±35.2 mg. While P. margaritifera seed and spat can successfully cultured in the hatchery and long-line hanging culture ground, poor larval survival and slow growth seem to be the limiting factors to support a pearl aquaculture industry in FSM.