quality; scoring for lustre, surface perfection, main colour, tint, shape, diameter, length and weight. Inserted beads ranged from 6.3–7.8 mm diameter and their size was not correlated
significantly with shell size. Relaxant use was associated with significantly higher mortality in Ž
. both Groups of oysters and total failures deaths q bead rejections in Group II oysters compared
with controls. Relaxant use was also associated with pearls of significantly lighter weight, i.e., with lower nacre secretion, further suggesting that there was an adverse effect from this treatment.
Ž .
Adhesive use was associated with more deaths significant in Group II and with more bead Ž
. rejections significant in Group I . Adhesive use, however, had a positive effect on pearl quality
through improved shape. Seventy-six of the 78 Group I oysters that retained beads for 6 weeks Ž
. had formed pearl sacs, but 55 of the beads 71 already had imperfections in the form of
projecting calcified ‘tails’ from the bead. Histological examination showed that the ‘tails’ enclosed accumulations of inflammatory cells in the incision pathway. Adhesive use significantly
reduced the prevalence of beads with ‘tails’, apparently by better closing the incision pathway. The reduction in ‘tails’ at 6 weeks was reflected in a significant reduction in the mean
lengthrdiameter ratio of pearls at harvest, i.e., a higher level of symmetry. This was the only significant, positive effect of the three treatments on pearl quality parameters. Antiseptic applica-
tion to the operation site had no significant effect on mortality, bead rejection rate or ‘tail’ formation. However, antiseptic was the only treatment that resulted in a lower percentage of total
failures compared to controls. Inflammatory cells, arising from suspected bacterial infections, were associated with failures to produce a pearl sac and the ‘tails’ imperfection. Better hygiene
with beads, instruments, cloths, cutting boards and graft tissue 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. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: Pearl; Bivalve; Pinctada; Technique; Relaxation; Antisepsis; Incision
1. Introduction
Ž .
Cultured black pearls from Pinctada margaritifera Linnaeus are a significant
industry for peoples of the Southern Pacific. Currently, French Polynesia produces in excess of US117 million annually, while the Cook Islands produce some US2.6
Ž .
million Anon, 1996 . Other Pacific countries have become interested in pearl produc- tion. In countries that are remote from major air routes, cultured pearls offer a high
value, non-perishable and small volume and weight commodity that is suited for culture in many of their coral lagoons.
The basic technique for round pearl formation in Pinctada species was developed by Ž
Japanese biologists many years ago and is used by most pearl technicians Anon, 1991; .
Gervis and Sims, 1992 . Briefly, it may include a period during which the oyster is ‘conditioned’ to weaken it prior to the operation. The oyster is then forced open and an
incision is made in the gonad. A small piece of mantle from another oyster together with Ž
. a bead or nucleus of shell is inserted through the incision. The oyster is then returned
to the sea. There it is suspended from long-lines or rafts or rested on the substrate for up to 2 years, during which time the pearl forms.
Pearl formation requires the inserted mantle tissue to form a complete sac around the shell bead and to secrete successive layers of nacre onto the bead. The nacreous mantle
epithelium spreads around the nucleus until it encloses the nucleus. This has been Ž
. reported to take from 3 days Wada, 1968 in the Japanese pearl oyster P. imbricata
Ž .
Ž .
refer Shirai, 1994 to 23 days Scoones, 1996 in P. maxima. An organic periostracal Ž
. layer s conchiolin and a prismatic layer of calcite crystals are then laid down. After
Ž about 40 days, the nacreous layer of aragonite crystals begins to be secreted Kawakami,
. 1952 . However, this process of deposition may become defective and result in
Ž .
abnormal pearls Scoones, 1996 . Details of the three main types of pearl sac epithelium and the pearl layers produced by these sacs have been documented for P. imbricata
Ž .
Ž .
Aoki, 1966 and P. maxima Dix, 1972 . The three layers correspond to the three layers of pearl oyster shell, secreted by the mantle.
However, despite the relative success of this pearl formation method, substantial failures continue to occur, including mortalities from the surgery, bead rejection and
Ž .
poor quality pearls Cabral, 1990; Scoones, 1990; Wada, 1991; Scoones, 1996 . Virtu- ally no studies of factors influencing the outcome of the insertion operation in pearl
Ž .
oysters have been published. Meng and Xing 1991 is one example of a preliminary Ž
. study of factors influencing cultured pearls in P. margaritifera. Scoones 1996 also
studied the development of the pearl sac in P. maxima with reference to pearl defects. This study is part of a broader investigation into the application of surgical techniques
used in modern veterinary science to improve the quality and yield of cultured pearls. In particular, this experiment examined the effects of relaxation, antiseptic application and
incision closure on the round pearl formation technique, when these treatments were used in association with the bead insertion procedure in P. margaritifera.
2. Materials and methods
