A q u a cu ltu r e,16 (1 9 8 9 ) 4 3 -5 6 43 Elsevier S cien ce Publishers B .V ., Am sterdam -P rin ted in T h e N etherlands Larval and Juvenile Rearing of Black-Lip Pearl Oyster, Pinctada margaritifera (Linnaeus)K IN T R O D U C T IO NThe black-lip pearl oyster, P inctada m argaritifera (Linnaeus), is one of the three valuable species of pearl oyster for the cultured pearl industry of the world, the other two being P. m axim a (Jameson) and P. fucata (Gould). In India, P. m argaritifera is second in importance, after P. fucata. Its distribution is limited to the Andaman and Nicobar Islands ( Alagarswami, 1983); however, stray oysters may occasionally be collected from the Gulf of Mannar. The re source is not substantial in the islands; it is not exploited for the shell or the pearl, but collected by the Nicobarese for food. As a species native to the is-0044-84 8 6 /8 9 /$ 0 3 .50
A quaculture, 34 (1 9 8 3 ) 2 8 7-30 1 T he Indian pearl oyster Pinctada fucata w as spawned in the laboratory and the larvae w ere successfully reared to spat setting under tropical con dition s. T h e larve grow s through the straight-hinge, u m bo, eye sp ot and pediveliger stages in the pelagic phase b efore m etam orphosing to plantigrade and setting on a substratum as spat, and these stages are described. Large differences were n oticed in larval grow th w ithin and betw een fou r rearing experim ents. Isochrysis galbana was used as standard fo o d th roughou t larval rearing at a cell concentration range 8 0 -350/jul. Spatfall occu rred on day 24-32 o n a variety o f substrata. The highest density o f 4 .7 1 /cm * was observed on fibreglass tank b o tto m . G row th o f P. fucata larvae appears to be a step fu n ction , and that o f spat u p to 13 weeks describes a curvilinear form . IN TR O D U C TIO NFollow ing the developm ent o f techniques fo r farming o f pearl oyster Pinctada fucata and production o f cultured pearls in India (Alagarswami, 19 7 4 ), it became im portant to breed the species artificially as the popula tions in the natural beds display drastic fluctuations (Alagarswami and Qasim, 1973). Spat collection in inshore areas and bays yields only small quantities which com prise several species o f pearl oysters with a low per centage o f P. fucata (Alagarswami, 19 7 7 ). M ethods fo r controlled spawn ing o f pearl oyster were developed earlier (Alagarswami et al., 1980a) and larval rearing cou ld be carried o u t only up to the straight-hinge stage (Ala garswami et al., 1980b). Subsequently success has been achieved in produc tion o f pearl oyster spat in the experiments described in this paper.The few works on breeding o f the Japanese pearl oyster (Kobayashi, 0 0 4 4 -8 4 8 6 /8 3 /$ 0 3 .0 0
The Indian pearl oyster Pinctada fucata (Gould) is typically capable of producing pearls of 3-5 mm diameter. The feasibility of production of pearls similar to Akoya pearls of 6-8 mm diameter was studied from the southwest coast of India. Along with this, mortality and retention rates of implanted oysters, rate of nacre production, thickness of nacre deposited, quality and type of pearls produced and effect of hydrographic variations on the mortality of implanted oysters were also studied. A total of 706 oysters were implanted, 311 with 5 mm, 395 with 6 mm nuclei and stocked in 30 cages for a period of 317 days. The mortality rates were highest, 0.173 ± 0.22 for the 6 mm nucleus implanted oysters followed by 5 mm nucleus implanted oysters at 0.107 ± 0.025 during the first 30 days after implantation. These rates were significantly different (P b 0.05) from the mortality rate of the control oysters (0.042 ± 0.04). The retention rates based on the surviving oysters, ranged from 33 to 61% (average 45.9 for 5 mm) and 31 to 60% (average 48.9% for 6 mm). The nacre deposition rates on the nuclei were found to be 4.0 ± 1.0 μm day − 1 and 3.0 ± 1.0 μm day − 1 for 6 and 5 mm nuclei respectively. Of the total 131 pearls obtained, 27.6% were A-grade, 31.3% B-grade, 19.8% C-grade, 7.6% baroques and 13.7% rejects or trash. The total suspended solids (TSS) in the water were found to be positively correlated (P b 0.05) with the monthly mortality rate of the implanted oysters. The study showed that it was possible to obtain relatively thick nacre within a short period of 10 months, the deposition rate being about 9 times higher than that observed in Japanese waters and 2.2 to 2.3 times more than that along the Indian southeast coast.
Biofouling on the periostracum of pearl oysters and on the cages has been considered as a stress factor causing mortality of the farmed stock, reducing growth rates and also affecting pearl quality. In farming experiments using the pearl oyster, Pinctada fucata, at Kollam Bay (India), biofouling was found to be a problem. This study was conducted to understand the effect of fouling on the mortality of pearl oysters kept in suspended culture, to identify the main foulers, the seasonal variation in biofouling and species successions in the community with reference to abiotic factors. The average monthly mortality rate (MR) was estimated as 0.117 ± 0.002 and the monthly variations were significantly different (P < 0.01). The total fouling (0.163 ± 0.002 g/g oyster) and biofouling weights (0.166 ± 0.007 g/g oyster) were high in December when the fouling community was composed of several species and dominated by the ascidian, Didemnum sp. December was also the period when the MRs peaked indicating that this organism was the main cause of mortality in pearl farms in Kollam Bay. A clear seasonality in the fouling community (25 species belonging to nine phyla) has been observed in the present study. On the basis of this study, monthly cleaning of oysters is advocated except during December, January, and March when the cleaning should be fortnightly.
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