Variation in clearance and ingestion rates by larvae of the black-lip pearl oyster (Pinctada margaritifera, L.) feeding on various microalgae

Clearance rate (CR) and ingestion rate (IR) of different sizes (89, 125 and 188 μm shell length) of Pinctada margaritifera larvae were determined when feeding on various microalgae. The microalgae tested were the diatoms, Chaetoceros muelleri and C. simplex, and flagellates, Tahitian Isochrysis aff. galbana, Pavlova lutheri and P. salina at 5 or 10 cells μL^–1. Both CR and IR of microalgae tested in this study increased with increasing larval size; but at all larval sizes, diatoms resulted in lower CR and IR. Of the microalgae tested, P. margaritifera larvae showed greatest CR and IR with the two Pavlova spp. Maximum CR for P. salina was 10.5, 21.2 and 29.7 μL h^–1 for larvae with shell lengths of 89, 125 and 188 μm, respectively. The highest IR values for P. margaritifera larvae with shell lengths of 89, 125 and 188 μm were 8.7, 81.0 and 165.7 cells·larva^–1 h^–1, respectively. CR and IR of P. salina were approximately five times higher than those recorded for C. muelleri and C. simplex.     

The combined effects of temperature and salinity on embryos and larvae of the black-lip pearl oyster, Pinctada margaritifera (L.)

This paper reports on a 4 × 4 factorial design experiment conducted to examine the combined effects of temperature and salinity on embryonic development and growth and survival of black-lip pearl oyster, Pinctada margaritifera (L.) larvae. The temperatures used were 20 °C, 25 °C, 30 °C and 35 °C, and the salinities were 25°/_oo, 30°/_oo, 35°/_oo and 40°/_oo. Response surface contour diagrams were generated from the survival and growth data to estimate optimal conditions. Normal development of embryos occurred only from 25 °C to 30 °C. The optimal conditions for maximum survival and growth were 26–29 °C and 28–32°/_oo. Temperatures of 35 °C or greater were lethal for larvae and, at all temperatures tested, larval growth and survival were lowest at a salinity of 40°/_oo.     

Evaluation of partial substitution of live algae with dried Tetraselmis for larval rearing of black-lip pearl oyster, Pinctada margaritifera (L.)

Experiments were conducted with larvae of theblack-lip pearl oyster, Pinctadamargaritifera fed on a regime of living algae(an equal mixture of Tahitian Isochrysisaff. galbana and Pavlova salina)either partially or completely substituted withheterotrophically grown spray-dried algae (Tetraselmis suecica). Two experiments wereconducted; in the first, 1-day old larvae werecultured for 13 days and, in the second, 13days old larvae were culture for 7 days. Inboth experiments larvae were fed the followingproportions of live algae (LA) and dried Tetraselmis (DT); (1) 100% LA, (2) 75% LA +25% DT, (3) 50% LA + 50% DT, (4) 25% LA +75% DT; and (5) 100% DT. The optimal dietsfor maximum larval growth were 100% LA and75% LA + 25% DT resulting in larvae with amean shell length (SL) of 132 ± 3.8 and 131± 2.7 µm, respectively, at day 13. Thisshowed that 25% substitution of livemicro-algae with DT is possible withoutaffecting growth of P. margaritiferalarvae of less than 150 µm SL. There was nosignificant difference in survival of P.margaritifera larvae fed 100% LA, 75% LA +25% DT and 50% LA + 50% DT over a period of13 days. Highest survival (43.7%) occurred inlarvae fed 100% DT while lowest (approximately18%) occurred in controls (50% livemicro-algae and unfed) during the firstexperiment. The result of the second experimentindicated that with increasing size, larvae arecapable of accepting a higher proportion ofdried Tetraselmis in their diet. Therewere no significant differences in larvalgrowth or survival, between treatments where LAwas partially and completely substituted dietswith DT.     

The effects of dietary supplements of polyunsaturated fatty acid on pearl oyster,Pinctada margaritifera L., gonad composition and reproductive output

Black‐lip pearl oyster, Pinctada margaritifera broodstock was collected from the wild. Egg production, hatching rate and larval development were compared between oysters induced to spawn within 2 days after collection in the wild (T1), oysters fed a pure microalgae diet during 24 days before spawning (T2) and oysters fed the same microalgal diet in which 10% of the algae were replaced with 2 μm polyunsaturated fatty acid (PUFA)‐rich microspheres (T3). Administration of lipid microspheres resulted in larger sized eggs, a higher percentage of D‐larvae and larger sized 48‐h‐old larvae (P<0.05). The total and neutral lipid contents of the gonad increased after oysters were fed with microalgae only or with supplementary diet. The major neutral and polar fractions of saturated fatty acid (SFA) were 16C and 18C fatty acids, and not influenced by the diet (P>0.05). The gonads of oysters fed supplementary PUFA contained more docosahexaenoic acid (DHA) and less monounsaturated fatty acids. Higher level of DHA in gonads of T3 was associated with oogenesis and embryogenesis success. The n‐3/n‐6 ratio in the neutral lipid fraction provides a good indication of the spawning condition and predicting egg size and hatching rate.     

珠母贝幼虫运动、自然沉降及摄食行为

主要通过分析幼虫形态变化、幼虫运动、自然沉降及摄食行为等生物学信息,为珠母贝(Pinctada margaritifera)幼虫培育设施及饵料投喂策略提供优化思路。在显微镜下观察不同日龄幼虫形态变化、幼虫运动状态、测量幼虫运动速率,观察幼虫静置下自然沉降及幼虫对单胞藻摄食过程。结果显示,幼虫依靠面盘外周纤毛摆动维持运动并完成摄食,运动时幼虫开壳朝上,壳顶朝下,面盘伸出壳外牵引幼虫运动。俯视观幼虫绕一定半径的圆顺时针方向运动,垂直方向螺旋上升或下降。水平运动速率范围246.88~3641.94μm/s,运动速率v(μm/s)与壳长l(μm)之间存在的关系为v=-0.0841l2+37.2690l-2149.1031(R~2=0.9707),运动速率与环绕半径显著相关(P0.05)。随着幼虫生长,体重增加,面盘逐渐退化,面盘纤毛摆动难以维持幼虫悬浮,静置时幼虫沉降率增加,13 dph(days post hatching,孵化后天数)后沉降至底部的幼虫壳长显著(P0.05)大于悬浮幼虫。幼虫饵料投喂过多,导致饵料不消化或不完全消化就排出体外,以致摄食的饵料不能完全消化利用。     

Abnormal periostracum secretion during the mineralization process of the pearl in the blacklip pearl oyster Pinctada margaritifera

Whitish parasite-like bodies (PLBs), 0.5–2 μm in size, were detected within the pearl bag of some grafted pearl oysters, Pinctada margaritifera, from Takapoto island (French Polynesia). Histological and ultrastructural investigations have revealed that these bodies consisted of lamellar organic material locally secreted by some epithelial cells of the pearl bag. The fine structure and the formation of these bodies are described. The causes of this abnormal secretion of organic mater, which actually corresponds to periostracum, are not presently known. No parasite nor infectious micro-organism was found associated with the PLBs.     

Changes in fatty acid and sterol composition during oogenesis in the pearl oyster Pinctada margaritifera

The fatty acid and sterol composition of the oyster Pinctada margaritifera during oogenesis and in eggs was analysed. No major differences were observed during oogenesis, but the egg composition was significantly different from that of gonads. The amount of saturated fatty acids was the highest in eggs and the C16:0 predominant (P<5%); by contrast, the amount of 22:6(n‐3) was significantly lower (P<5%) than in gonads. No major differences were observed for the polar lipid (PL) composition during oogenesis. The main free sterols in gonads and eggs were cholesterol and brassicasterol. Among free sterols, the proportion of cholesterol diminished continuously from the beginning to the end of gonad maturation, and this decrease persisted in eggs after spawning. Cholesterol represented 40% to 55% of the sterol ester encountered in gonad and eggs. This study allowed us to investigate the fatty acid and sterol composition during oogenesis of the pearl oyster P. margaritifera, leading to a clearer understanding of the nutritional requirements of pearl oyster during the reproduction process.     

Quantification of eggs and sperm in the Black-lip pearl oyster Pinctada margaritifera using an enzyme-linked immunosorbent assay (ELISA)

We have developed immunological probes to quantify eggs and sperm of the Black-lip pearl (BLP) oyster Pinctada margaritifera. The western blot assay revealed that the polyclonal antibodies developed in this study specifically recognized only egg and sperm proteins. These polyclonal antibodies also showed high sensitivities to the antigens, detecting 0.31–10 μg/ml of the egg or sperm proteins in an indirect enzyme-linked immunosorbent assay (ELISA). Accordingly, we used an indirect ELISA to quantify the eggs and sperm in BLP oysters collected in December 2009 from Weno Island in Micronesia and in May 2010 from Tahiti. The gonad somatic index (GSI), a ratio of gonad weight to somatic tissue weight, of the females collected from Weno Island ranged from 3.6 to 18.4 %, while the GSI of the females collected from Tahiti ranged from 5.6 to 12.6 %. Similarly, the GSI of the male BLP oysters from Weno Island ranged from 0.8 to 8.5 %, while the GSI of the males from Tahiti ranged from 4.8 to 7.5 %. These results lead to the conclusion that the immunological probes developed in this study can be successfully applied to quantify BLP oyster gonadal tissues and that these probes can be used in studies of BLP oyster reproductive ecology based on their sensitivity, rapidity, and affordability.     

Age‐dependence of cultured pearl grade and colour in the black‐lipped pearl oyster Pinctada margaritifera

Pinctada margaritifera is an economically important marine bivalve species for cultured pearl production in French Polynesian aquaculture. In order to evaluate the influence of donor oyster age on pearl quality traits, experiments were conducted over 6 years using both grafts and surgreffe operations. At harvest, six pearl quality traits were recorded and compared: surface defects, lustre, grade, darkness level and visual colour. Analysing the quality traits of pearls harvested in the initial graft process and those of pearls obtained from surgreffe experiments allowed a comparison of the influence of pearl sac cells originating from the initial mantle graft, which aged together with their recipient oysters. The results demonstrated a significant decrease between these successive grafts in lustre, grade (A‐B‐C), darkness level, and green colour – traits that are of major importance in the pearl market. The duplicated graft experiment allowed the comparison of donor oyster families at 2 and 5 years old, where a mantle graft was inserted into recipient oysters aged 2.5 years. The results showed the same tendencies to a lesser extent, with (i) an improved pearl grade, predominantly through a most important rate of 0 surface defect category, and (ii) a green/grey ratio in favour of the younger donor. A comparison between the graft‐surgreffe and the duplicated graft experiments also highlighted: (i) the indirect role played by the younger recipient oysters, which must be optimized for optimal pearl quality realization, and (ii) the complex interplay between the donor and recipient oysters.     

Genetic linkage map of the pearl oyster,Pinctada martensii (Dunker)

Genetic linkage maps were constructed with amplified fragment length polymorphism (AFLP) and microsatellite markers for the pearl oyster, Pinctada martensii (Dunker), the main bivalve used for marine pearl production in Asia. Twenty‐four AFLP and 84 microsatellite primer pairs were used for linkage analysis in a full‐sib family with two parents and 78 offspring. Of the 2357 AFLP fragments generated, 394 (16.7%) were polymorphic and segregating. Most (340 or 86.2%) of the markers segregated according to expected Mendelian ratios. Female and male linkage maps were constructed using 230 and 189 markers, including 15 and 10 microsatellites respectively. The female map consisted of 110 markers in 15 linkage groups, covering 1415.9 cM, with an average interval of 14.9 cM. The male map consisted of 98 markers in 16 linkage groups, with a total length of 1323.2 cM and an average interval of 16.1 cM. When unlinked doublets were considered, genome coverages were 78.5% for the female and 73.5% for the male map. Although preliminary, the genetic maps constructed here should be useful for future linkage and quantitative trait loci mapping efforts.     

Influence of nacre deposition rate on cultured pearl grade and colour in the black-lipped pearl oyster Pinctada margaritifera using farmed donor families

Cultured pearl nacre deposition rate in Pinctada margaritifera oysters was studied to examine its influence on Tahitian classification grade and colour and to further our understanding of using selected donor oysters produced in a hatchery system for the improvement of these traits. A large-scale grafting experiment using 150 farmed donor oysters was realised in Rangiroa atoll (French Polynesia). After 18 months of culture, 874 pearls were harvested and 7 pearls quality traits were recorded: (1) nacre deposition rate assessed by nacre thickness and weight, (2) classification grade, lustre and surface defects, and (3) colour assessed by pearl colour darkness level and visual colour categories. Nacre deposition rate significantly influence pearl grade, surface defects, darkness level and colour categories, but not the lustre. Grade A pearls had the thickest and heaviest nacre on average, compared with grade D pearls and rejects. In addition, pearls without any surface defect had thicker and heavier nacre. Pearls with low darkness were the thinnest and the lightest. Pearls of aubergine–peacock secondary colours were the thickest and the heaviest. These results highlight the importance of rapid nacre deposition rate for increasing the production of grade A pearls, with less surface defects and dominance of a black tone colour. Fast nacre deposition may, however, have a negative impact on other pearl quality traits, such as pearl lustre. This study demonstrates the importance of examining relationships between pearl quality traits in a way that provides solid information that can be directly used for breeding and genetic selection programmes.     

Phenotypic indicators for cultured pearl size improvement in the black‐lipped pearl oyster (Pinctada margaritifera): towards selection for the recipient growth performance

The black‐lipped pearl oyster, Pinctada margaritifera, is the most important farmed species in French Polynesia and the basis of the most valuable export industry. Mass production of black pearls relies on a surgical operation requiring tissue from a donor pearl oyster to be grafted, together with a nucleus made of shell, into the gonad of a recipient oyster. Improving pearl size through family selection remains one of the main challenges for future aquaculture development. This study analyses the relative contribution of donor and recipient oysters to pearl size. To this end, hatchery‐produced donor oysters of two batches, large and small (based on shell height), were used to supply grafts for recipients, which were then monitored individually for their growth performance by recording shell height, width, and thickness, and total live weight (flesh + shells) every 6 months (four biometric measurement times) over 20 months of culture. Pearls issued from the two batches of donors showed no significant differences in nacre weight or thickness. In contrast, recipient oyster shell height and total weight were increasingly positively correlated with these pearl size parameters over the culture period, becoming significant at 8 months post‐grafting. Potential therefore exists to use shell height and oyster weight as phenotypic indicators for selective breeding of recipient oysters with high growth performance to increase pearl size in P. margaritifera.     

Impact of season and grafter skill on nucleus retention and pearl oyster mortality rate in Pinctada margaritifera aquaculture

The mollusc Pinctada margaritifera is the top economic aquaculture species in French Polynesia (export value) and forms the basis of the black pearl industry. Mass production of this unique gem, produced by a living organism, relies on a surgical operation requiring tissue from a donor pearl oyster to be grafted, together with a nucleus made of shell, into the gonad of a receiving pearl oyster. This technique is performed by expert grafters, whose work constitutes the first step influencing pearl farm production yield. This study makes the first report of effects mediated by individual grafters and by the season of grafting on three rates scored at 45 days post operation: nucleus retention, nucleus rejection and pearl oyster mortality. These results were obtained in a very large scale grafting experiment, designed and conducted in a single culture site in the atoll of Arutua (Tuamotu Archipelago) and involving a total of 52,910 grafts performed by ten professional grafters, during two contrasting seasons: autumn (four grafting experiments) and spring (three grafting experiments). Statistical analysis using linear mixed-effect model for both univariate and multivariate analysis was performed. The results show a very highly significant season effect (p < 0.001), with a higher rate of nucleus retention in autumn than spring: 91.1 versus 79.4 %, respectively. A very highly significant season effect was also recorded for nucleus rejection rate (p < 0.001), which was greater in spring than in autumn: 12.6 versus 7.7 %. Oyster mortality rate was up to six times higher in spring than in autumn (p < 0.001). Within the two seasons, there was no significant difference between the grafting experiments for any of the three variables, adding robustness to the inter-season results. Taking into account this seasonal variation effect, grafter skill had a significant impact on the three variables (p < 0.001), making it possible to rank grafters from most to least efficient. Aside from skill differences between grafters, grafting in autumn may significantly increase graft success. Water temperature and its indirect consequences could be one of the most important environmental factors implicated in overall efficiency. These findings may help the potential development of an annual grafting schedule according to season/ lagoon temperature as a way to maximize production yield for the black-lipped pearl oyster industry in French Polynesia.     

Cost–benefit analysis of two culture methods that influence pearl production from the black‐lip pearl oyster,Pinctada margaritifera

The black‐lip pearl oyster, Pinctada margaritifera, used for round pearl production in Polynesia, is generally cultured using “ear‐hanging” where they are attached to a rope to form “chaplets.” In other countries, pearl oysters are cultured using panel (pocket) nets that are more expensive than chaplets but afford more protection to cultured oysters. Prior research has shown panel nets produce pearls of higher quality and value, potentially generating higher profits. This study used cost–benefit analysis to compare pearl production using chaplet‐based and panel net‐based culture methods. Whole farm data, including gross revenues and annual production costs, fixed and variable, were analyzed. Average production cost per pearl using panel net‐based culture was USD 22.47 and for chaplet‐based culture was USD 21.55. However, use of panel nets saved around 3,430 hr (USD 6,860) of labor a year, offsetting the greater capital investment. A chaplet‐based pearl farm generated USD 65,738 in annual profits compared to USD 88,774 for a panel net‐based farm. Positive cash flow was achieved 1 year earlier (Year 7) for the panel net‐based farm. This is the first economic analysis of different pearl culture methods for P. margaritifera and evidence of profitability will support further development of the black‐lip pearl industry in the Indo‐Pacific region.     

Estimating the heritability for growth-related traits in the pearl oyster,Pinctada fucata martensii (Dunker)

Twelve paternal half-sib families (or 36 full-sib families) of the pearl oyster, Pinctada fucata martensii (Dunker), were produced according to the requirements of hierarchical genetic mating design. A total of 4320 individuals, aged 15 months, were measured for seven growth-related traits. Predicated upon the additive-dominance genetic analysis model, varying genetic variance components and then heritabilities of the growth-related traits of interest were estimated using analysis of variance. Results showed that seven growth-related traits had larger additive genetic variances (P<0.05); the dominance genetic variance of shell weight (SW) was smaller (P>0.05), the dominance genetic variances of other six traits were all larger (P<0.05). Narrow- and broad-sense heritabilities for the seven traits were, respectively, 0.64 ± 0.10 and 0.78 ± 0.12 for shell length, 0.49 ± 0.06 and 0.63 ± 0.09 for shell height, 0.38 ± 0.14 and 0.54 ± 0.16 for shell breadth, 0.41 ± 0.17 and 0.56 ± 0.11 for hinge length, 0.53 ± 0.11 and 0.68 ± 0.08 for body weight, 0.35 ± 0.07 and 0.55 ± 0.08 for tissue weight and 0.67 ± 0.10 and 0.75 ± 0.16 for SW. All heritability estimates were statistically significant (P<0.05). According to these results, the mass selection procedure is suggested for the breeding of P. martensii.     

Fouling and predation; how do they affect growth and survival of the blacklip pearl oyster, Pinctada margaritifera, during nursery culture?

This paper reports on 5 experiments conducted to assess the effect of cleaning regime and predation on growth and survival of blacklip pearl oyster (Pinctada margaritifera) juveniles in north Queensland, Australia. P. margaritifera juveniles with a mean (±SE) dorso-ventral shell height (DVH) of 4.5 ± 0.1 mm were placed into plastic mesh trays and cleaned either every 4 or 8 weeks or left uncleaned for 16 weeks. Cleaning regime had a significant effect on growth and survival (P < 0.005). Lowest DVH (16.2 ± 1.0) was shown by oysters in uncleaned trays during 16 weeks compared to oysters in cleaned trays; however, there was no significant difference in DVH between oysters held in trays cleaned every 4 (19.4 ± 1.2) or 8 weeks (21.2 ± 0.8). In contrast lowest survival was shown by oysters held in trays that were cleaned every 4 weeks (30 ± 5%), but no differences were noted between oysters cleaned every 8 weeks (63 ± 4%) and oysters that were left uncleaned for 16 weeks (75 ± 8%). Predators of P. margaritifera in northern Australia included crabs, stomatopods, flatworms, gastropods and fish. The stomatopod, Gonodactylus falcatus, was the most destructive predator with individuals consuming in excess of 20 juvenile pearl oysters per week. The leather jacket, Paramonocanthus japonicus, did not kill pearl oysters, but trimmed the margin of oysters shells significantly reducing DVH when compared to control groups cultured without fish. Removing predators monthly had a significant effect on growth of pearl oysters compared to oysters in non-inspected trays; however monthly inspection of culture trays did not significantly improve oyster survival. This revised version was published online in August 2006 with corrections to the Cover Date.