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.
The e¡ect of temperature on the development, growth, survival and settlement of Perna viridis was studied under controlled conditions to provide information needed for the development of commercial hatchery technology for green mussel P. viridis. Total mortality of the larvae occurred after 24 h at temperatures of 33 1C and 35 1C. At 24 1C, larvae took longer to settle than at temperatures of 27 1C, 29 1C and 31 1C. For optimum larval development (8^13 h), growth (17.270.84 mm day^1) and survival (55.27 0.84%), a hatchery rearing temperature of 31 1C is required. For settlement no signi¢cant di¡erence was seen between the percentage settlement at 29 1C (49.373.34%) and 31 1C (45.871.76%). However, the process of settlement began and ended earlier at 29 1C (from15 to18 days) than at 31 1C (from18 to 20 days). Thus for larval settlement a temperature of 29 1C is recommended.
SUMMARYThe rediscovery of Cluvngella (Dryopu) lata frcm Gulf ot Mannar, southeast coast of India and its anatomical features are discussed and described.The present report of this species from Gulf of Mannar establishes a prec se localitv for the first time. This snecies is regarded a s a true borer buried in massive scler3ctenian corals. Distinctive characters placing C. lutci in the subgenus El-yopn are disccssed in detail.
Comparative studies were made on the growth and biometric relationships of the pearl oyster Pinctada fucata (Gould) Tuticorin stock at (Tuticorin (TST)p arent stock) transplanted from the Tuticorin Bay (8.71N;78.21E) in the Gulf of Mannar along the Indian southeast coast to Kollam Bay (8.81N; 76.51E) in the Arabian Sea along the Indian southwest coast (Tuticorin stock at Kollam (TSK)^transplanted stock). At the time of transplantation, Kollam Bay did not have a native stock, however, within a year, the transplanted stock spawned and oyster spats were collected from within the farm (Kollam stock (KS)^progeny stock). The growth in dorso-ventral measurement and total weight in Kollam Bay was 1.4^1.6 times and 3.1to 6.8 times respectively greater than that observed at Tuticorin. Furthermore, at Kollam Bay, the thickness observed at the end of ¢rst year was similar to that obtained at the end of second year in Tuticorin. Both the TSK and KS had signi¢-cantly higher instantaneous growth rates (IGR) than TST. All the stocks displayed signi¢cantly di¡erent biometric relationships. The increased growth in Kollam Bay is attributed to the almost double productivity in the Arabian Sea compared with the Bay of Bengal. It is concluded that in the case of P. fucata, the site and its interaction with environment are important determinants of growth and shell dimensions. The present study clearly indicates that the environmental conditions prevailing along the southeast Arabian Sea are congenial for the growth, gametogenesis, spawning and settlement of P. fucata larvae. In spite of strong monsoonal in£uences in the hydrology of Kollam Bay, the growth and reproduction of P. fucata stocks indicates its relative hardiness and ability to adapt to a changed environment.
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