Approaches to improve cultured pearl formation in Pinctada margaritifera through use of relaxation, antiseptic application and incision closure during bead insertion

Three treatments were tested on blacklip pearl oysters, Pinctada margaritif era, during the bead insertion process as part of research to improve the e fficiency of round pearl culture. The oysters (100 to 150 mm shell height) were maintained on a commercial farm at Manihiki atoll, Cook Islands. The t hree treatments were: (1) immersion of the oysters in 2 ml/l propylene phen oxetol for 15 min to relax them before operating; (2) disinfection of the o peration site with an antiseptic (1:50 aqueous dilution of 10% povidone iod ine solution); and (3) closure of the surgical incision with a flexible cya noacrylate adhesive. The three treatments were applied or not applied to oy sters in a 3-factor arrangement to give eight treatment combinations. The t reatment combinations were applied to two groups of oysters: Group I, consi sting of 96 oysters (12 sets X 8 treatment combinations), and Group IJ, con sisting of 768 oysters (12 sets X 8 treatment combinations X 8 oysters per set). After 6 weeks, all oysters were inspected for mortality and bead reje ction, and Group I oysters were sacrificed. Group I oysters were necropsied and checked for the presence of pearl sacs. After 18 months, the pearls fr om Group II oysters were harvested and graded for quality; scoring for lust re, surface perfection, main colour, tint, shape, diameter, Length and weig ht. Inserted beads ranged from 6.3-7.8 mm diameter and their size was not c orrelated significantly with shell size. Relaxant use was associated with s ignificantly higher mortality in both Groups of oysters and total failures (deaths + bead rejections) in Group II oysters compared with controls. Rela xant use was also associated with pearls of significantly lighter weight, i .e., with lower nacre secretion, further suggesting that there was an adver se effect from this treatment. Adhesive use was associated with more deaths (significant in Group II) and with more bead rejections (significant in Gr oup I). Adhesive use, however, had a positive effect on pearl quality throu gh improved shape. Seventy-six of the 78 Group I oysters that retained bead s for 6 weeks had formed pearl sacs, but 55 of the beads (71%) already had imperfections in the form of projecting calcified 'tails' from the bead. Hi stological examination showed that the 'tails' enclosed accumulations of in flammatory cells in the incision pathway. Adhesive use significantly reduce d the prevalence of beads with 'tails', apparently by better closing the in cision pathway. The reduction in 'tails' at 6 weeks was reflected in a sign ificant reduction in the mean length/diameter ratio of pearls at harvest, i .e., a higher level of symmetry. This was the only significant, positive ef fect of the three treatments on pearl quality parameters. Antiseptic applic ation to the operation site had no significant effect on mortality, bead re jection rate or 'tail' formation. However, antiseptic was the only treatmen t that resulted in a lower percentage of total failures compared to control s. Inflammatory cells, arising from suspected bacterial infections, were as sociated with failures to produce a pearl sac and the 'tails' imperfection. Better hygiene with beads, instruments. cloths, cutting boards and graft t issue should control infection levels. The additional times taken to apply the three treatments of this study were not excessive and encourage further innovative approaches to the bead insertion process. (C) 2000 Elsevier Sci ence B.V. All rights reserved.