Pearls from the second graft were, as expected, larger than those
fromthe first graft because of the larger sized nuclei used in re-graft operations
(Haws, 2002). Our results also showed that there was an improvement
in the shape of pearls between the first and second grafts.
Most of the circled pearls harvested after the first graft were classed
into the ‘circle’ shape category (95%)with some in the ‘baroque’ category
(5%) but none in the ‘semi-round’ category. The shape composition of
these first graft pearls is to be expected because the oysters chosen for
the second graft were those that produced circled pearls after first
graft. Despite this, 18% of these oysters produced pearls of ‘semiround’
shape after the second graft demonstrating improvement in
pearl shape. There was also a major reduction in the number of pearls
with circles after the second graft. All pearls from the first graft had
varying numbers of circles and 86% of them had three or more circles.
In contrast, 50% of the pearls produced from the second graft did not
have any circles. Our data show for the first time that that production
of circled pearls after second graft is not obligatory for P. margaritifera
that produced circled pearls after the first graft.
Prior research in this laboratory involved histological analysis of developing
andmature pearl-sacs in an effort to identify whether anomalies
in pearl-sac structure were related to the production of circled
pearls (Kishore and Southgate, 2014, 2015).While no obvious structural
anomalies in the pearl-sac were identified, close proximity of byssus
threads to the pearl-sac in some samples indicated that perhaps pressure
applied to the pearl-sac by byssus or associatedmuscles may be involved
in circle formation (Kishore and Southgate, 2014). Accepting
that the nucleus or developing pearl rotates within the pearl-sac
(Cartwright et al., 2013), then pressure applied at a single point on the
pearl-sac could result in a concentric anomaly on the pearl. However,
if such amechanismwas responsible for circle formation on developing
pearls, a similar proportion of circled pearlswould be expected to result
from first and second grafts given that byssus and their associated muscles
would be present in the same or similar position during development
of both first graft and second graft pearls. Furthermore, because regrafting
involves implanting a larger (than the original) nucleus
and that the second pearl is likely to be larger than the first, it is
reasonable to assume that anomalies resulting from pressure applied
to the pearl-sac during pearl formation could be more evident in
second graft pearls.
An important factor that is likely to vary between first and second
grafts is the tightness and rigidity of the pearl-sac around the nucleus
following the second graft. Harvesting pearls involves an incision
made into the pearl-sac to remove themature pearl. A second larger nucleus
(generally of similar size to the harvested pearl) is then inserted
into the pearl-sac through the incision that will subsequently heal.
The pearl-sac that develops from the initial graft grows around the nucleus
(Kishore and Southgate, 2014) and subsequent and continual deposition
of nacre onto the nucleus is likely to result in increasing tension
within the pearl-sac. There is no doubt that cutting into the pearl-sac to
remove first graft pearls and subsequent insertion of a second nucleus
will result in changes in tension within the pearl-sac. Given that this
study has shown a reduction in the proportion of circled pearls following
second graft, it is likely that changes in pearl-sac tension resulting from
the second graft operation reduces or eliminates the factor(s) that cause
circles. If tension within the pearl-sac is a contributing factor in circle formation,
it would be interesting for future research to examine the influence
of nucleus size at second graft, which could be used to manipulate
pearl-sac tension, on the proportion of circled pearls produced.
We are unaware of any prior studies that have reported the relative
proportions of circled pearls produced for P.margaritifera following first
and second grafts. But a number have hypothesised the cause(s) of circles
which include the skills of grafting technicians, environment conditions at
pearl culture sites and grafting season (Ky et al., 2015), interruption in
the supply or changes in concentration of material(s) in the peal-sac
(Cartwright et al., 2013) and the presence of byssus close to the pearlsac
during pearl formation (Kishore and Southgate, 2014), as discussed
above. Higher levels of suspended particulate matter present in island lagoons
compared to atoll lagoons has been suggested as the cause of differences
in the proportion of pearls with circles produced in these two
environments (Ky et al., 2014b), and a higher proportion of circled pearls
are produced by oysters held on chaplets compared to those held in panel
(pocket) nets in Fiji (Kishore, unpublished data). It is likely that a number
of factors influence the formation of circles on cultured pearls produced
by P. margaritifera and further research is required.
This is the first study to report on differences in the overall quality
of first and second graft pearls produced by the same oysters
(P. margaritifera). Despite pearls from the second graft having improved
shape, size, and a reduced number of circles compared to
first graft pearls, there was no significant improvement in overall quality
of second graft pearls. However, of particularly importance is that our results
show thatmarketable pearls can be produced fromoysters that are
normally discarded after first pearl harvest and this has potential to generate
increased revenue for pearl farmers in Fiji and other Pacific islands.
Pearl farmers would need to consider the labour and financial inputs required
to replenish oysters discarded after the first pearl harvest versus
the potential revenue generated from re-grafting these oysters. A detailed
economic analysis of the two optionswould greatly benefit pearl farmers
ไข่มุกจากรับสินบนสองได้ คาด มีขนาดใหญ่กว่าจากรับสินบนแรกเนื่องจากแอลฟาขนาดใหญ่ที่ใช้ในการดำเนินงานใหม่ graft(Haws, 2002) ผลของเรายังพบว่า มีการปรับปรุงในรูปร่างของไข่มุกระหว่าง grafts และสองส่วนใหญ่ไข่มุกวนเก็บเกี่ยวหลังจากแรกรับสินบนได้ classedเป็น 'วงกลม' รูปร่างประเภท (95%) บางอย่างใน 'ยุคบาโรก'(5%) แต่ไม่มีในหมวด 'กึ่งกลม' รูปร่างส่วนประกอบของไข่มุกเหล่านี้รับสินบนแรกจะคาดหวังเนื่องจากหอยนางรมที่เลือกได้รับสินบนที่สองที่ผลิตไข่มุกวนหลังแรกรับสินบน แม้นี้ 18% ของหอยนางรมเหล่านี้ผลิตไข่มุกของ 'semiround'รูปร่างหลังจากรับสินบนสองที่เห็นในการปรับปรุงรูปมุก นอกจากนี้ยังมีจำนวนไข่มุกลดหลักกับวงหลังจากรับสินบนสอง รับสินบนแรกไข่มุกทั้งหมดได้จำนวนวงและ 86% ของพวกเขามีวงสาม หรือมากกว่าในทางตรงกันข้าม 50 ของไข่มุกที่ผลิตจากรับสินบนสองไม่วงกลมใด ๆ ได้ แสดงข้อมูลของเราในครั้งแรกเวลาที่ผลิตนั้นของไข่มุกวนหลังจากรับสินบนสองไม่บังคับสำหรับ P. margaritiferaที่ผลิตจัดไข่มุกหลังจากแรกรับสินบนก่อนการวิจัยในห้องปฏิบัติการนี้เกี่ยวข้องกับสรีรวิทยาวิเคราะห์พัฒนาถุงไข่มุก andmature ในความพยายามที่จะระบุว่าความผิดในโครงสร้างเพิร์ล sac เกี่ยวข้องกับการผลิตจัดpearls (Kishore and Southgate, 2014, 2015).While no obvious structuralanomalies in the pearl-sac were identified, close proximity of byssusthreads to the pearl-sac in some samples indicated that perhaps pressureapplied to the pearl-sac by byssus or associatedmuscles may be involvedin circle formation (Kishore and Southgate, 2014). Acceptingthat the nucleus or developing pearl rotates within the pearl-sac(Cartwright et al., 2013), then pressure applied at a single point on thepearl-sac could result in a concentric anomaly on the pearl. However,if such amechanismwas responsible for circle formation on developingpearls, a similar proportion of circled pearlswould be expected to resultfrom first and second grafts given that byssus and their associated muscleswould be present in the same or similar position during developmentof both first graft and second graft pearls. Furthermore, because regraftinginvolves implanting a larger (than the original) nucleusand that the second pearl is likely to be larger than the first, it isreasonable to assume that anomalies resulting from pressure appliedto the pearl-sac during pearl formation could be more evident insecond graft pearls.An important factor that is likely to vary between first and secondgrafts is the tightness and rigidity of the pearl-sac around the nucleusfollowing the second graft. Harvesting pearls involves an incisionmade into the pearl-sac to remove themature pearl. A second larger nucleus(generally of similar size to the harvested pearl) is then insertedinto the pearl-sac through the incision that will subsequently heal.The pearl-sac that develops from the initial graft grows around the nucleus(Kishore and Southgate, 2014) and subsequent and continual depositionof nacre onto the nucleus is likely to result in increasing tensionwithin the pearl-sac. There is no doubt that cutting into the pearl-sac toremove first graft pearls and subsequent insertion of a second nucleuswill result in changes in tension within the pearl-sac. Given that thisstudy has shown a reduction in the proportion of circled pearls followingsecond graft, it is likely that changes in pearl-sac tension resulting fromthe second graft operation reduces or eliminates the factor(s) that causecircles. If tension within the pearl-sac is a contributing factor in circle formation,it would be interesting for future research to examine the influenceof nucleus size at second graft, which could be used to manipulatepearl-sac tension, on the proportion of circled pearls produced.We are unaware of any prior studies that have reported the relativeproportions of circled pearls produced for P.margaritifera following firstand second grafts. But a number have hypothesised the cause(s) of circleswhich include the skills of grafting technicians, environment conditions atpearl culture sites and grafting season (Ky et al., 2015), interruption inthe supply or changes in concentration of material(s) in the peal-sac(Cartwright et al., 2013) and the presence of byssus close to the pearlsacduring pearl formation (Kishore and Southgate, 2014), as discussedabove. Higher levels of suspended particulate matter present in island lagoonscompared to atoll lagoons has been suggested as the cause of differencesin the proportion of pearls with circles produced in these twoenvironments (Ky et al., 2014b), and a higher proportion of circled pearlsare produced by oysters held on chaplets compared to those held in panel(pocket) nets in Fiji (Kishore, unpublished data). It is likely that a numberof factors influence the formation of circles on cultured pearls producedby P. margaritifera and further research is required.This is the first study to report on differences in the overall qualityof first and second graft pearls produced by the same oysters(P. margaritifera). Despite pearls from the second graft having improvedshape, size, and a reduced number of circles compared tofirst graft pearls, there was no significant improvement in overall qualityof second graft pearls. However, of particularly importance is that our resultsshow thatmarketable pearls can be produced fromoysters that arenormally discarded after first pearl harvest and this has potential to generateincreased revenue for pearl farmers in Fiji and other Pacific islands.Pearl farmers would need to consider the labour and financial inputs requiredto replenish oysters discarded after the first pearl harvest versusthe potential revenue generated from re-grafting these oysters. A detailedeconomic analysis of the two optionswould greatly benefit pearl farmers
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