Anaesthetic induced relaxation of the winged pearl oyster, Pteria penguin, varies with oyster size and anaesthetic concentration

Stress and mortality of pearl oysters during nucleus implanting for round pearl and mabé pearl production can be reduced using appropriate anaesthetics that allow improved access to nucleus implanting sites. This study evaluated the efficacy of three different concentrations of benzocaine (0.25, 0.50 and 1.20 g L-1) and 1-propylene phenoxetol (2.50, 3.00 and 3.50 mL L-1) when presented to ‘small’ (dorso-ventral height [DVH], 78.7 ± 1.6 mm), ‘medium’ (DVH, 118.2 ± 2.0 mm) and ‘large’ (DVH, 149.3 ± 1.1 mm) cohorts of the winged pearl oyster, Pteria penguin. Results showed the following general trends across treatments with both anaesthetics: (1) greater proportions of large oysters became relaxed compared to small oysters; (2) large oysters required shorter exposure times to become relaxed than small oysters; (3) for each size class of oyster, an increase in anaesthetic concentration resulted in an increased proportion of relaxed oysters; and (4) ‘mantle collapse’ (where the mantle collapses away from the shell) was only recorded in large oysters in treatments with higher concentrations of anaesthetics. The most effective concentration of benzocaine to use with small, medium and large Pt. penguin was the highest level tested in this study (1.20 g L-1). Similarly, the highest concentration of 1-propylene phenoxetol tested (3.5 mL L-1) was also the most effective with all three size classes of Pt. penguin. These treatments caused mantle collapse in large oysters, for which use of lower, less effective anaesthetic concentrations may be considered preferable, to avoid potentially negative impacts of mantle collapse on subsequent mabé pearl production. As well as efficacy, choice of anaesthetic should consider ease of preparation and preparation time. Benzocaine requires dissolving in methyl alcohol and heating to 88–92˚C, while 1-propylene phenoxetol is readily soluble in seawater

Epistaxis: the cause found beyond the nose

Renal cell carcinoma (RCC) is a malignant disease that is often diagnosed at a metastatic stage. The head and neck represent up to 3% of the metastatic RCC, and the paranasal sinus area is one of the least involved sites. Here, we introduce the case of a 74-year-old female patient who presented with a history of traumatic nasal bleed. A cranial computed tomography scan and magnetic resonance imaging showed a fronto-ethmoidal mass with pachymeningeal involvement. A nasal biopsy from the paranasal sinuses was taken. On histopathological examination, metastatic clear cell carcinoma was the main hypothesis, which later was confirmed to be RCC on immunohistochemistry. On further radiological examination, an exophytic mass was depicted in the kidney’s upper and middle pole. The patient had no renal complaints and was asymptomatic. Fronto-ethmoidal sinus is a rare site for metastatic RCC, especially in cases where the patient is asymptomatic. Early detection by keeping RCC metastasis as the differential diagnosis in such cases can lead to early treatment and improve the overall survival of the patient

Prognostic model to predict postoperative acute kidney injury in patients undergoing major gastrointestinal surgery based on a national prospective observational cohort study.

Background: Acute illness, existing co-morbidities and surgical stress response can all contribute to postoperative acute kidney injury (AKI) in patients undergoing major gastrointestinal surgery. The aim of this study was prospectively to develop a pragmatic prognostic model to stratify patients according to risk of developing AKI after major gastrointestinal surgery. Methods: This prospective multicentre cohort study included consecutive adults undergoing elective or emergency gastrointestinal resection, liver resection or stoma reversal in 2-week blocks over a continuous 3-month period. The primary outcome was the rate of AKI within 7 days of surgery. Bootstrap stability was used to select clinically plausible risk factors into the model. Internal model validation was carried out by bootstrap validation. Results: A total of 4544 patients were included across 173 centres in the UK and Ireland. The overall rate of AKI was 14·2 per cent (646 of 4544) and the 30-day mortality rate was 1·8 per cent (84 of 4544). Stage 1 AKI was significantly associated with 30-day mortality (unadjusted odds ratio 7·61, 95 per cent c.i. 4·49 to 12·90; P < 0·001), with increasing odds of death with each AKI stage. Six variables were selected for inclusion in the prognostic model: age, sex, ASA grade, preoperative estimated glomerular filtration rate, planned open surgery and preoperative use of either an angiotensin-converting enzyme inhibitor or an angiotensin receptor blocker. Internal validation demonstrated good model discrimination (c-statistic 0·65). Discussion: Following major gastrointestinal surgery, AKI occurred in one in seven patients. This preoperative prognostic model identified patients at high risk of postoperative AKI. Validation in an independent data set is required to ensure generalizability

Improving the quality of cultured round pearls produced by Pinctada margaritifera in Fiji (Linnaeus, 1758)

The pearl industry is recognised as one of the most profitable in the aquaculture sector. In many countries it makes up a large segment of the aquaculture sector and in French Polynesia for example, it is the second highest export earner (after tourism) and makes a substantial contribution to the country's economy and to the livelihoods of its people. The major products of the marine pearl industry are Akoya pearls, white South Sea Pearls, and 'black' South Sea Pearls pearls, otherwise known as Tahitian pearls that are produced almost exclusively in the Pacific. 'Black' South Sea Pearls produced by the black-lip pearl oyster Pinctada margaritifera are the focus of this study. At present, the proportion of high quality 'black' pearls in any pearl farm is very low making up to only around 3%-5% of the total harvest, yet earning around 95% of farm revenue. A major influence on the high proportion of low quality pearls is the presence of 'circles' or concentric depressions or grooves on surfaces that reduce pearl values considerably. Reducing the proportion of these low quality pearls by a small proportion would significantly increase the profit margin of a 'black' pearl farm. This study aimed to identify the causes of low quality 'black' pearls, particularly circles, and provide a basis for improved pearl grafting and oyster husbandry practices supporting increased production and revenue for pearl farmers. In Chapter 2, pearl-sac development after grafting in P. margaritifera was studied in detail for the first time. A total of 110 P. margaritifera with a mean (± SE) anteroposterior measurement of 110.82 ± 0.41 mm and dorso-ventral measurement of 112.06 ± 0.45 mm were grafted to allow histological examination and chronological description of pearl-sac development in this species. Beginning two days after grafting, oysters were sacrificed regularly until the 48th day and the pearl-sacs of sampled oysters were sectioned and analysed. The graft tissue proliferated and developed into a complete pearl-sac within 14 days of grafting when the epithelial cells responsible for nacre secretion were fully developed. However, first nacre secretion onto the nucleus was not observed until 32 days after grafting. Furthermore, the presence of byssus in close proximity of developing pearl-sac was demonstrated in this study; a factor that has the potential to impact pearl-sac development affecting even nacre deposition and resulting pearl quality. Haemocytes were also present with clumps or aggregations noted in some pearl-sacs. The findings reported in this Chapter provide a more detailed understanding of pearl-sac development in P. margaritifera and a basis for future research towards developing improved pearl culture practices and pearl quality. A detailed examination of haemocyte accumulation during pearl-sac formation provided the basis for Chapter 3. The level of haemocytes present in the pearl-sacs decreased overtime in many oysters with the samples from day two showing the highest levels. Such a trend generally supports the development of a spherical shaped pearl-sac that would form a regular shaped pearl. However, in some oysters, clumps of haemocytes persisted for a period longer than expected causing a bulge in the pearl-sacs. The pearl-sacs grew over the clumps that resulted in a deformity to what should have been spherical shaped pearl-sacs. Pearls produced from such misshapen pearl-sacs often have calcified "tails" or be of baroque shapes with much reduced values. The exact cause(s) of varying levels of haemocyte accumulation during pearl-sac development in P. margaritifera is not known. However, it is reasonable to assume that haemocyte production is positively related to the degree of damage caused to host oyster tissues during the grafting procedure. While haemocytes have an important wound healing role in pearl oysters, excessive haemocyte presence may be detrimental to maximizing pearl quality. The feasibility of using regenerated graft tissue for pearl production in P. margaritifera was investigated in Chapter 4. Twelve days after grafting with regenerated graft tissue, there was complete encapsulation of the nucleus by the fully developed pearl-sac and the first layer of organic matrix had been secreted. Sixteen days after grafting, the pearl-sac was completely integrated with host tissue and could no longer be distinguished as foreign. The epithelial cells in the pearl-sac continued to secrete the organic matrix layer but there were no signs of nacre deposition at this stage. However, after three months of culture, nuclei in oysters grafted with regenerated mantle tissue were completely covered with nacre. The average nacre thickness on pearls produced from regenerated (0.55 ± 0.01 mm, n = 8) and normal (0.53 ± 0.01 mm, n = 8) mantle tissue did not differ significantly (p > 0.05). Nacre secretion rates, over the 80 day period subsequent to pearl-sac formation were 6.84 ± 0.1 μm day⁻¹ and 6.66 ± 0.1 μm day⁻¹ for oysters grafted with regenerated and normal mantle tissue, respectively. Again, these means were not significantly different (p = 0.258). These results clearly showed that regenerated mantle tissue can function successfully as saibo for pearl production in P. margaritifera. This finding could provide significant benefits to pearl farmers and provide a basis for further development of current pearl grafting practices. It is widely assumed that P. margaritifera producing low quality pearls with circles are unlikely to produce pearls with improved quality if grafted again for pearl production. Such oysters are often discarded. However, if these oysters are capable of improved pearl quality when re-grafted, then this would provide opportunities for improved income for pearl farmers. Chapter 5 aimed to determine whether oysters producing circled pearls are able to produce pearls with improved quality after re-grafting. A total of 100 oysters that produced circled pearls and would have normally been discarded were re-grafted and the quality of successive pearls produced by individual oysters was compared in terms of shape, size, lustre, colour, surface perfection and overall quality. The proportion of pearls with circles decreased from 95% of first graft pearls to 48% after the second graft, and 18% of second graft pearls were classified as 'semi-round' and superior in shape to all first graft pearls. There was a significant improvement (p = 0.04) in the overall shape of second graft pearls compared to first graft pearls. The highest proportion of pearls (63%) from the first graft were 10-11 mm in size while the majority of second graft pearls (51%) were 11-12 mm in size, and the differences in pearl size between first and second graft were significant (p = 0.04). Second graft pearls had poorer lustre than first graft pearls with a higher proportion of dull pearls, a lower proportion of medium lustre pearls and no pearls with high lustre. Despite this, the number of pearls in different lustre categories after the first and second graft did not differ significantly (p = 0.07). For overall grading, most first graft pearls (83%) were assessed as 'C' grade with 17% categorised as 'D' grade. Similarly, most second graft pearls (78%) were assessed as 'C' grade and 20% as 'D' grade; however, 2% of pearls were assessed as 'B' grade which were not present in first graft pearls. Nonetheless, the number of pearls belonging to different grades was not significant (p = 0.08). The data in chapter 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 first graft. The data further show that marketable pearls can be produced from oysters that are normally discarded after the first pearl harvest and this has potential to generate increased revenue. The potential effects of byssus production on the development or function of normal pearl-sacs was determined in Chapter 6. This was done after byssus was observed in close proximity to developing pearl-sacs in the experiment reported in Chapter 2. This Chapter investigated the impacts of relative current strength and different culture units on byssus secretion by P. margaritifera. Oysters were either 'ear–hung' or housed in panel nets before being transported to low (Nawi) and high (Raviravi) current sites. The quantity of new byssus produced by oysters in the two culture units at the two sites was counted 5, 10, 15 and 20 days after deployment. At the end of the experiment, the thicknesses and tensile strengths of randomly selected byssal threads from ear-hung oysters and oysters held in panel nets were determined. Ten days after deployment, there was no significant difference in the quantity of byssus produced by oysters in the two types of culture units at both sites. An average of around two threads per byssus secreting oyster was recorded by the tenth day. However, after 15 and 20 days, earhung oysters had produced significantly more byssus (p < 0.01) than those housed in panel nets at the high current site. On the twentieth day, ear-hung oysters had an average of six byssal threads while those housed in panel nets had an average of around three per oyster at the Raviravi site. In contrast, production of byssus by oysters in the two types culture units did not differ significantly for the same period at the low current site. Furthermore, ear-hung oysters produced significantly thicker byssus than those held in panel nets (p = 0.01) which had significantly high tensile strengths (p = 0.01). It is hypothesised that secretion of an increased number of byssal threads by earhung oysters is a response to a greater degree of agitation than those held in panel nets. This could be one of the reasons for anecdotal commentary relating to the production of a high proportion of pearl with inferior quality by oysters cultured using the 'earhanging' method. With oysters cultured using chaplets producing more byssus compared to oysters housed in panel nets, the experiment described in Chapter 7 was designed to determine if oysters held in panel nets produced higher quality pearls with fewer circles compared to oysters that were ear-hung on chaplets. Six hundred P. margaritifera were grafted for the first time and cultured using panel nets or chaplets at three commercial farm sites to determine if these different culture methods influence resulting pearl quality. The pearls produced were compared in terms of size, shape, lustre, colour, surface perfection and overall quality. The highest proportion of pearls produced in all treatments was in the 10-11 mm size category (37% to 54%) but culture method did not significantly (p = 0.211) influence the size of pearls produced. Oysters held on chaplets produced more pearls with concentric surface grooves or circles (47% to 60%) compared to oysters in held panel nets (43% to 45%) at all three culture sites. Oysters held in panel nets produced higher proportions of pearls in the more desirable 'round' and 'semi-round' shape categories (6% and 25%, respectively) than oysters held on chaplets (5% and 15%, respectively) at all three culture sites, and culture methods had a significant impact (p = 0.031) on pearl shape overall. Higher proportions of pearls in the 'very high' and 'high' lustre categories (8% and 40%, respectively) were produced by oysters held in panel nets compared to those on chaplets (3% and 16%, respectively) at each of the three culture sites. However, the overall impact of culture methods on pearl lustre was not significant (p = 0.100). At all three culture sites, higher proportions of pearls assigned to grades 'A' (6%) and 'B' (46%) were produced by oysters in panel nets compared to those held on chaplets where 3% and 29% of pearls were assigned to grade 'A' and grade 'B', respectively. Oysters held on chaplets produced higher proportions of grade 'C' (49%) and grade 'D' (19%) pearls than those in panel nets (39% and 9%, respectively) at all three culture sites. The grades of pearls were significantly influenced (p = 0.035) by culture method. The results of this experiment clearly demonstrated the benefits of pearl production using panel nets compared to the traditional chaplet-based system used by the majority of pearl farmers in Fiji and throughout the Pacific. Pearls production using panel nets will provide better returns with higher profit margins for pearl farmers but requires greater outlay for infrastructure and labour that may be beyond the scope of most pearl farmers in Fiji and the Pacific. A detailed cost-benefit analysis of the two husbandry options would be beneficial to pearl farmers. This study addressed factors affecting the quality of cultured 'black' pearls through a number of experiments that assessed the impacts of both developmental and biological factors (e.g. pearl-sac development and function, oyster response to culture method and culture environment) as well as husbandry and culture conditions (e.g. culture method and current strength) on pearl production and pearl quality. The major applications of the results of this study are: (1) potential use of saibo donors producing high quality pearls for multiple saibo donations potentially improving the proportion of high quality pearls; (2) production of marketable pearls from oysters that are normally discarded after the first pearl harvest resulting in increased production and revenue; and (3) change to a panel net-based culture system resulted in higher pearl quality and a ~30% increase in the value of pearls produced. These findings provide a good basis for increased pearl production in Fiji and for future research in this field

Improving the quality of cultured round pearls produced by Pinctada margaritifera in Fiji (Linnaeus, 1758)

The pearl industry is recognised as one of the most profitable in the aquaculture sector. In many countries it makes up a large segment of the aquaculture sector and in French Polynesia for example, it is the second highest export earner (after tourism) and makes a substantial contribution to the country's economy and to the livelihoods of its people. The major products of the marine pearl industry are Akoya pearls, white South Sea Pearls, and 'black' South Sea Pearls pearls, otherwise known as Tahitian pearls that are produced almost exclusively in the Pacific. 'Black' South Sea Pearls produced by the black-lip pearl oyster Pinctada margaritifera are the focus of this study. At present, the proportion of high quality 'black' pearls in any pearl farm is very low making up to only around 3%-5% of the total harvest, yet earning around 95% of farm revenue. A major influence on the high proportion of low quality pearls is the presence of 'circles' or concentric depressions or grooves on surfaces that reduce pearl values considerably. Reducing the proportion of these low quality pearls by a small proportion would significantly increase the profit margin of a 'black' pearl farm. This study aimed to identify the causes of low quality 'black' pearls, particularly circles, and provide a basis for improved pearl grafting and oyster husbandry practices supporting increased production and revenue for pearl farmers. In Chapter 2, pearl-sac development after grafting in P. margaritifera was studied in detail for the first time. A total of 110 P. margaritifera with a mean (± SE) anteroposterior measurement of 110.82 ± 0.41 mm and dorso-ventral measurement of 112.06 ± 0.45 mm were grafted to allow histological examination and chronological description of pearl-sac development in this species. Beginning two days after grafting, oysters were sacrificed regularly until the 48th day and the pearl-sacs of sampled oysters were sectioned and analysed. The graft tissue proliferated and developed into a complete pearl-sac within 14 days of grafting when the epithelial cells responsible for nacre secretion were fully developed. However, first nacre secretion onto the nucleus was not observed until 32 days after grafting. Furthermore, the presence of byssus in close proximity of developing pearl-sac was demonstrated in this study; a factor that has the potential to impact pearl-sac development affecting even nacre deposition and resulting pearl quality. Haemocytes were also present with clumps or aggregations noted in some pearl-sacs. The findings reported in this Chapter provide a more detailed understanding of pearl-sac development in P. margaritifera and a basis for future research towards developing improved pearl culture practices and pearl quality. A detailed examination of haemocyte accumulation during pearl-sac formation provided the basis for Chapter 3. The level of haemocytes present in the pearl-sacs decreased overtime in many oysters with the samples from day two showing the highest levels. Such a trend generally supports the development of a spherical shaped pearl-sac that would form a regular shaped pearl. However, in some oysters, clumps of haemocytes persisted for a period longer than expected causing a bulge in the pearl-sacs. The pearl-sacs grew over the clumps that resulted in a deformity to what should have been spherical shaped pearl-sacs. Pearls produced from such misshapen pearl-sacs often have calcified "tails" or be of baroque shapes with much reduced values. The exact cause(s) of varying levels of haemocyte accumulation during pearl-sac development in P. margaritifera is not known. However, it is reasonable to assume that haemocyte production is positively related to the degree of damage caused to host oyster tissues during the grafting procedure. While haemocytes have an important wound healing role in pearl oysters, excessive haemocyte presence may be detrimental to maximizing pearl quality. The feasibility of using regenerated graft tissue for pearl production in P. margaritifera was investigated in Chapter 4. Twelve days after grafting with regenerated graft tissue, there was complete encapsulation of the nucleus by the fully developed pearl-sac and the first layer of organic matrix had been secreted. Sixteen days after grafting, the pearl-sac was completely integrated with host tissue and could no longer be distinguished as foreign. The epithelial cells in the pearl-sac continued to secrete the organic matrix layer but there were no signs of nacre deposition at this stage. However, after three months of culture, nuclei in oysters grafted with regenerated mantle tissue were completely covered with nacre. The average nacre thickness on pearls produced from regenerated (0.55 ± 0.01 mm, n = 8) and normal (0.53 ± 0.01 mm, n = 8) mantle tissue did not differ significantly (p > 0.05). Nacre secretion rates, over the 80 day period subsequent to pearl-sac formation were 6.84 ± 0.1 μm day⁻¹ and 6.66 ± 0.1 μm day⁻¹ for oysters grafted with regenerated and normal mantle tissue, respectively. Again, these means were not significantly different (p = 0.258). These results clearly showed that regenerated mantle tissue can function successfully as saibo for pearl production in P. margaritifera. This finding could provide significant benefits to pearl farmers and provide a basis for further development of current pearl grafting practices. It is widely assumed that P. margaritifera producing low quality pearls with circles are unlikely to produce pearls with improved quality if grafted again for pearl production. Such oysters are often discarded. However, if these oysters are capable of improved pearl quality when re-grafted, then this would provide opportunities for improved income for pearl farmers. Chapter 5 aimed to determine whether oysters producing circled pearls are able to produce pearls with improved quality after re-grafting. A total of 100 oysters that produced circled pearls and would have normally been discarded were re-grafted and the quality of successive pearls produced by individual oysters was compared in terms of shape, size, lustre, colour, surface perfection and overall quality. The proportion of pearls with circles decreased from 95% of first graft pearls to 48% after the second graft, and 18% of second graft pearls were classified as 'semi-round' and superior in shape to all first graft pearls. There was a significant improvement (p = 0.04) in the overall shape of second graft pearls compared to first graft pearls. The highest proportion of pearls (63%) from the first graft were 10-11 mm in size while the majority of second graft pearls (51%) were 11-12 mm in size, and the differences in pearl size between first and second graft were significant (p = 0.04). Second graft pearls had poorer lustre than first graft pearls with a higher proportion of dull pearls, a lower proportion of medium lustre pearls and no pearls with high lustre. Despite this, the number of pearls in different lustre categories after the first and second graft did not differ significantly (p = 0.07). For overall grading, most first graft pearls (83%) were assessed as 'C' grade with 17% categorised as 'D' grade. Similarly, most second graft pearls (78%) were assessed as 'C' grade and 20% as 'D' grade; however, 2% of pearls were assessed as 'B' grade which were not present in first graft pearls. Nonetheless, the number of pearls belonging to different grades was not significant (p = 0.08). The data in chapter 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 first graft. The data further show that marketable pearls can be produced from oysters that are normally discarded after the first pearl harvest and this has potential to generate increased revenue. The potential effects of byssus production on the development or function of normal pearl-sacs was determined in Chapter 6. This was done after byssus was observed in close proximity to developing pearl-sacs in the experiment reported in Chapter 2. This Chapter investigated the impacts of relative current strength and different culture units on byssus secretion by P. margaritifera. Oysters were either 'ear–hung' or housed in panel nets before being transported to low (Nawi) and high (Raviravi) current sites. The quantity of new byssus produced by oysters in the two culture units at the two sites was counted 5, 10, 15 and 20 days after deployment. At the end of the experiment, the thicknesses and tensile strengths of randomly selected byssal threads from ear-hung oysters and oysters held in panel nets were determined. Ten days after deployment, there was no significant difference in the quantity of byssus produced by oysters in the two types of culture units at both sites. An average of around two threads per byssus secreting oyster was recorded by the tenth day. However, after 15 and 20 days, earhung oysters had produced significantly more byssus (p < 0.01) than those housed in panel nets at the high current site. On the twentieth day, ear-hung oysters had an average of six byssal threads while those housed in panel nets had an average of around three per oyster at the Raviravi site. In contrast, production of byssus by oysters in the two types culture units did not differ significantly for the same period at the low current site. Furthermore, ear-hung oysters produced significantly thicker byssus than those held in panel nets (p = 0.01) which had significantly high tensile strengths (p = 0.01). It is hypothesised that secretion of an increased number of byssal threads by earhung oysters is a response to a greater degree of agitation than those held in panel nets. This could be one of the reasons for anecdotal commentary relating to the production of a high proportion of pearl with inferior quality by oysters cultured using the 'earhanging' method. With oysters cultured using chaplets producing more byssus compared to oysters housed in panel nets, the experiment described in Chapter 7 was designed to determine if oysters held in panel nets produced higher quality pearls with fewer circles compared to oysters that were ear-hung on chaplets. Six hundred P. margaritifera were grafted for the first time and cultured using panel nets or chaplets at three commercial farm sites to determine if these different culture methods influence resulting pearl quality. The pearls produced were compared in terms of size, shape, lustre, colour, surface perfection and overall quality. The highest proportion of pearls produced in all treatments was in the 10-11 mm size category (37% to 54%) but culture method did not significantly (p = 0.211) influence the size of pearls produced. Oysters held on chaplets produced more pearls with concentric surface grooves or circles (47% to 60%) compared to oysters in held panel nets (43% to 45%) at all three culture sites. Oysters held in panel nets produced higher proportions of pearls in the more desirable 'round' and 'semi-round' shape categories (6% and 25%, respectively) than oysters held on chaplets (5% and 15%, respectively) at all three culture sites, and culture methods had a significant impact (p = 0.031) on pearl shape overall. Higher proportions of pearls in the 'very high' and 'high' lustre categories (8% and 40%, respectively) were produced by oysters held in panel nets compared to those on chaplets (3% and 16%, respectively) at each of the three culture sites. However, the overall impact of culture methods on pearl lustre was not significant (p = 0.100). At all three culture sites, higher proportions of pearls assigned to grades 'A' (6%) and 'B' (46%) were produced by oysters in panel nets compared to those held on chaplets where 3% and 29% of pearls were assigned to grade 'A' and grade 'B', respectively. Oysters held on chaplets produced higher proportions of grade 'C' (49%) and grade 'D' (19%) pearls than those in panel nets (39% and 9%, respectively) at all three culture sites. The grades of pearls were significantly influenced (p = 0.035) by culture method. The results of this experiment clearly demonstrated the benefits of pearl production using panel nets compared to the traditional chaplet-based system used by the majority of pearl farmers in Fiji and throughout the Pacific. Pearls production using panel nets will provide better returns with higher profit margins for pearl farmers but requires greater outlay for infrastructure and labour that may be beyond the scope of most pearl farmers in Fiji and the Pacific. A detailed cost-benefit analysis of the two husbandry options would be beneficial to pearl farmers. This study addressed factors affecting the quality of cultured 'black' pearls through a number of experiments that assessed the impacts of both developmental and biological factors (e.g. pearl-sac development and function, oyster response to culture method and culture environment) as well as husbandry and culture conditions (e.g. culture method and current strength) on pearl production and pearl quality. The major applications of the results of this study are: (1) potential use of saibo donors producing high quality pearls for multiple saibo donations potentially improving the proportion of high quality pearls; (2) production of marketable pearls from oysters that are normally discarded after the first pearl harvest resulting in increased production and revenue; and (3) change to a panel net-based culture system resulted in higher pearl quality and a ~30% increase in the value of pearls produced. These findings provide a good basis for increased pearl production in Fiji and for future research in this field

Haemocyte persistence after grafting for pearl production in Pinctada margaritifera (Linnaeus, 1758)

The grafting process used for pearl production in pearl oysters triggers a significant haemocyte response which has an influence on the quality of pearls formed. One hundred and ten selected healthy adult Pinctada margarinfera were grafted for pearl production. Beginning two days after grafting, oysters were sacrificed regularly until the 48th day and the pearl-sacs of sampled oysters were sectioned for histological analysis. The level of haemocytes present in the pearl-sacs decreased overtime with the samples from day 2 showing the highest levels. Haemocyte levels also varied between samples from a particular day. The exact cause(s) of varying levels of haemocyte accumulation during pearl-sac development in P. margaritifera is not known. However, it is reasonable to assume that haemocyte production is positively related to the degree of damage caused to host oyster tissues during the grafting procedure. While haemocytes have an important wound healing role in pearl oysters, excessive haemocyte presence may be detrimental to maximizing pearl quality

Does the quality of cultured pearls from the black-lip pearl oyster, Pinctada margaritifera, improve after the second graft?

It is widely assumed that pearl oysters, Pinctada margaritifera, producing low quality pearls with concentric grooves or 'circles' are unlikely to produce pearls with improved quality if grafted again for pearl production. Such oysters are often discarded. However, if these oysters are capable of improved pearl quality when re-grafted, this would provide opportunities for improved income for pearl farmers. This study aimed to determine whether oysters producing circled pearls are able to produce pearls with improved quality after re-grafting. A total of 100 oysters that produced circled pearls and would have normally been discarded were re-grafted and the quality of successive pearls produced by individual oysters was compared in terms of shape, size, lustre, colour, surface perfection and overall quality. The proportion of pearls with circles decreased from 100% of first graft pearls to 48% after the second graft, and 18% of second graft pearls were classified as 'semi-round' and superior in shape to all first graft pearls. There was a significant improvement (p = 0.04) in the overall shape of second graft pearls compared to first graft pearls. The highest proportion of pearls (63%) from the first graft were 10-11 mm in size while the majority of second graft pearls (51%) were 11-12 mm in size, and the differences in pearl size between first and second graft were significant (p = 0.04). Second graft pearls had poorer lustre than first graft pearls with a higher proportion of dull pearls, a lower proportion of medium lustre pearls and no pearls with high lustre. Despite this, the number of pearls in different lustre categories after the first and second graft did not differ significantly (p = 0.07). For overall grading, most first graft pearls (83%) were assessed as 'C' grade with 17% categorised as 'D' grade. Similarly, most second graft pearls (78%) were assessed as 'C' grade and 20% as 'D' grade; however, 2% of pearls were assessed as 'B' grade which were not present in first graft pearls. Nonetheless, the number of pearls belonging to different grades was not significant (p = 0.08). 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 first graft. They further show that marketable pearls can be produced from oysters that are normally discarded after the first pearl harvest and this has potential to generate increased revenue.\ud \ud Statement of relevance:\ud \ud This paper presents novel new information on whether P. margaritifera that produced circled pearls after first grafting will produce pearls with improved quality when re-grafted. It clears the confusion among pearl farmers on the decision of whether or not to re-graft P. margaritifera that produced low quality pearls with high number of circles. Overall, the study has a positive impact on pearl aquaculture

A detailed description of pearl-sac development in the black-lip pearl oyster, Pinctada margaritifera (Linnaeus 1758)

Appropriate development of the pearl-sac in pearl oysters is an important factor influencing the quality of cultured pearls. In this study, a total of 110 black-lip pearl oysters (Pinctada margaritifera) with a mean (± SE) antero-posterior measurement of 110.82 ± 0.41 mm and dorso-ventral measurement of 112.06 ± 0.45 mm were grafted to allow histological examination and chronological description of pearl-sac development in this species. Beginning 2 days after grafting, oysters were sacrificed regularly until the 48th day and the pearl-sacs of sampled oysters were sectioned and examined. Graft tissue proliferated and developed into a complete pearl-sac within 14 days of grafting when the epithelial cells responsible for nacre secretion were fully developed. However, first nacre secretion onto the nucleus was not observed until 32 days after grafting. The presence and accumulation of haemocytes in the pearl pouch initially and in the pearl-sac thereafter is one of the primary factors potentially affecting pearl quality. Clumps of haemocytes present between the pearl-sac and nucleus caused distension of the pearl-sac from an ideally spherical shape. Furthermore, the presence of byssus in close proximity to the developing pearl-sac was demonstrated in this study. This has the potential to impact pearl-sac formation and resulting pearl quality. The findings reported in this paper provide a more detailed understanding of pearl-sac development in P. margaritifera and a basis for future research towards developing improved pearl culture practices and pearl quality

The effect of different culture methods on the quality of round pearls produced by the black-lip pearl oyster Pinctada margaritifera (Linnaeus, 1758)

A range of culture units and husbandry methods may be used for pearl oysters and the two most commonly used for Pinctada margaritifera are panel nets and chaplets. In this study, six hundred P. margaritifera were grafted for the first time and cultured using panel nets or chaplets at three commercial farm sites to determine if these different culture methods influences resulting pearl quality. The pearls produced were compared in terms of size, shape, lustre, colour, surface perfection and overall quality. The highest proportion of pearls produced in all treatments was in the 10–11 mm size category (37–54%) but culture method did not significantly (p = 0.211) influence the size of pearls produced. Oysters held on chaplets produced more pearls with concentric surface grooves or 'circles' (47–60%) compared to oysters in held panel nets (43–45%) at all three culture sites. Oysters held in panel nets produced higher proportions of pearls in the more desirable 'round' and 'semi-round' shape categories (6% and 25%, respectively) than oysters held on chaplets (5% and 15%, respectively) at all three culture sites, and culture method had a significant impact (p = 0.031) on pearl shape overall. Higher proportions of pearls in the 'very high' and 'high' lustre categories (8% and 40%, respectively) were produced by oysters held in panel nets compared to those on chaplets (3% and 16%, respectively) at each of the three culture sites. However, the overall impact of culture methods on pearl lustre was not significant (p = 0.100). At all three culture sites, higher proportions of pearls assigned to grades 'A' (6%) and 'B' (46%) were produced by oysters in panel nets compared to those held on chaplets where 3% and 29% of pearls were assigned to grade 'A' and grade 'B', respectively. Oysters held on chaplets produced higher proportions of grade 'C' (49%) and grade 'D' (19%) pearls than those in panel nets (39% and 9%, respectively) at all three culture sites. The grades of pearls were significantly influenced (p = 0.035) by culture method. This study clearly demonstrated the benefits of pearl production using panel nets compared to the traditional chaplet-based system used by the majority of pearl farmers in Fiji and throughout the Pacific. Pearls production using panel nets will provide better returns with higher profit margins for pearl farmers but requires greater outlay for infrastructure and labour that may be beyond the scope of most pearl farmers in Fiji and the Pacific. A detailed cost–benefit analysis of the two husbandry options would be beneficial to pearl farmers

Development and function of pearl-sacs grown from regenerated mantle graft tissue in the black-lip pearl oyster, Pinctada margaritifera (Linnaeus, 1758)

Current pearl grafting techniques were developed in the early 1900s and have changed little since. They involve the sacrifice of donor pearl oysters to provide graft tissue (saibo) that is implanted into host oysters. This study assessed the feasibility of using regenerated graft tissue for pearl production in the ‘black-lip’ pearl oyster, Pinctada margaritifera. Twelve days after grafting with regenerated graft tissue, there was complete encapsulation of the nucleus by the fully developed pearl-sac and the first layer of organic matrix had been secreted. Sixteen days after grafting, the pearl-sac was completely integrated with host tissue. The epithelial cells in the pearl-sac continued to secrete the organic matrix layer but there were no signs of nacre deposition at this stage. However, after three months of culture, nuclei in oysters grafted with regenerated mantle tissue were completely covered with nacre. The average nacre thickness on pearls produced from regenerated (0.547 ± 0.01 mm, n = 8) and normal (0.532 ± 0.01 mm, n = 8) mantle tissue did not differ significantly (p > 0.05). Nacre secretion rates, over the 80 day period subsequent to pearl-sac formation were 6.84 ± 0.1 μm day⁻¹ and 6.66 ± 0.1 μm day⁻¹ for oysters grafted with regenerated and normal mantle tissue, respectively. These means were not significantly different (p = 0.258). Our results clearly show that regenerated mantle tissue can function successfully as saibo for pearl production in P. margaritifera. This finding could provide significant benefits to pearl farmers and a basis for further development of current pearl grafting practices