Spat Settlement and Growth of Yearling of the Pearl Oyster Pinctada radiata in Bahrain Water PDF

Keywords

Spat settlement, growth, temperature, pearl oyster, Pinctada radiata, Bahrain

Abstract

Pearl oyster spat (Pinctada radiata) settlement under different environmental conditions was studied at several locations around Bahrain during 1989. A variety of spat collectors were tested and evaluated. Collectors made from empty oyster shell, nylon rope, coir rope type, steel wire, plastic baskets, wooden frames and cement coated oyster cages were laid during July 1989 at Fasht Al-Jarim, Khor Fasht, Sitra Beason, Buoy No. 3 and Ras Hayan. Spat settlement took place over a long period (July to November 1989)as evident from occurrence of small-sized oysters each time collectors removed but intense spat settling was recorded throughout August 1989 giving indirect evidence that spawning commenced toward end of July 1989, and August 1989. Although settlement was reported on a wide range substrates, empty oyster shells enhanced maximum settlement (80 spat per oyster shell) indicating that ready to sit larvae exhibited some degree of substrate preference by settling primarily on rough surfaces such as empty shells. Moreover most of the settlement took place in the mid-depth (0.5-1.5 m) region. However, based on average of 50 spat per shell, a total of 1 million spat could be conveniently collected using collectors made of empty oyster shells during settlement season. Spatial differences in spat settlement was recorded with Fasht Al-Jarim exhibiting heaviest settlement of larvae drifted from offshore oyster beds, in the north and northwest areas of Bahrain. Seasonal changes in pattern of post settlement growth was found to be closely related to changes in water temperature, as indicated by Spearman's correlation coefficient r = 0.5 at p < 0.05. After settlement in summer (July - August 1989) the spat showed accelerated rate of growth (0.204 - 0.248 mm/day) until the following winter (December- January) when growth has slowed down but at steadily rate mainly as a result of drop in water temperature from 27 - 33°C to 17 - 18°C, respectively. Eighteen months after settlement a shell length of 57.69 mm was attained, and there was an indication that growth slowed down during the second year.