Due to the expensiveness in rearing of the Akoya pearl oyster P. fucata from the stage of spat to implantable size in the sea for pearl production, an optimization of its rearing technology bears significant economic implications. Adults of P. fucata were strip spawned and the larvae were reared in the hatchery to produce spat. Growth trials were conducted on different age groups and the first attempt was done on spats with an average DVM of 3.99 mm, HL of 3.94 mm, THK of 1.25 mm and WGT of 0.008 g. The first study was a comparative growth analysis between spat grown in one tone FRP tanks (≈25000 spats) in hatchery and those that reared in micron meshed cages (stocked with≈25000 spats) under open sea conditions. Triplicates were maintained for each culture containers. The micron meshed cages had dimensions of 93 cm length with corresponding diameter of 10 cm made of filter cloth of mesh size of 1 x 1 mm and the duration of this study was for a period of three months. During the third month, results showed that spats grown in micron meshed cages showed increments in their growth by 7.83 mm (DVM), 4.86 mm (HL), 1.61 mm (THK) and 0.192 g (WGT) whereas those grown in FRP tanks grew only by 0.95 mm (DVM), 0.5 mm (HL), 0.46 mm (THK) and 0.004 g (WGT) indicating faster growth in open sea conditions. Results were statistically analysed using One Way ANOVA tests and found to be statistically significant at P < 0.001. Results of T-test analysis also support the above results.
Second study involves the effect of stocking density on the growth and survival of juveniles reared in plastic baskets of different stocking densities viz; 200, 300, 400, 500, 600, 700, 800, 900 and 1000. Initial growth of spats recorded during the time of transfer to plastic baskets was an average of 11.78 mm (DVM), 8.5 mm (HL), 2.81 mm (THK) and 0.136 g (WGT). The plastic baskets used for rearing had a diameter of 24 cm, height of 13.5 cm and a total volume of 6104.16 cm3. The total available opening of a plastic basket was 700 cm2. It has rows of rectangular openings of size 1cm x 1cm on the body and 1cm x 0.5 cm openings on the lid. During the first month the baskets were covered with mosquito netting of mesh size, 1 mm in order to prevent the loss of small spats through the basket openings. Results showed that P.fucata juveniles can be reared in stocking densities up to 400 for a period of five months indicating 90% rate of survival without much drop in growth. By the fifth month, an average net increase of 32.59 mm (DVM), 29.71 mm (HL), 13.64 mm (THK) and 10.48 g (WGT) was observed in growth of juveniles stocked in stocking density 200 and augmentation of those stocked in stocking density 400 increased with 27.12 mm (DVM), 22.82 mm (HL), 12.27 mm (THK) and 7.094 g (WGT) which implies the significant role of stocking density in P. fucata culture system. Results of the One Way ANOVA tests conducted were also found to be statistically significant at P < 0.001.
Third study was performed on the growth of P. fucata sub adults reared in box cages of different stocking densities viz; 200, 300, 400, 500, 600, 700, 800, 900 and 1000. And the initial growth recorded at the time of transfer to box cages were as; an average DVM of 36.56 mm, an average HL of 29.98 mm, an average thickness of 12.73 mm and an average weight of 6.62 g. The box cages used had dimensions of 50 cm X 50 cm X 12 cm with a mesh size of 25 mm. During the fifth month results showed 98% survival rate in corresponding stocking densities of 200, 300 and 400. No significant difference was noted in DVM, HL and THK of oysters stocked in stocking densities of 300 and 400; whereas an inverse relationship was noted in average weight and increasing stocking densities. The increments in growth of sub adults recorded was as in stocking density 200 : 23.51 mm (DVM), 20.81 mm (HL), 12.29 mm (THK) and 20.7 g (WGT), in stocking density 300 : 17.03 mm (DVM),10.16 mm (HL),10.07 mm (THK) and 12.95 g (WGT), in stocking density 400 was 16.09 mm (DVM), 10.15 mm (HL), 5.12 mm (THK) and 12.03 g (WGT) during the fifth month indicating that increasing stocking densities exerts a negative effect on the growth of P. fucata under culture. Results were statistically analysed using One Way ANOVA tests and found to be statistically significant at p < 0.001.