Silver-lip Pearl Oyster Research Articles

Xenografts and pearl production in two pearl oyster species, P. maxima and P. margaritifera: Effect on pearl quality and a key to understanding genetic contribution

Mantle xenografts between two Pinctada pearl oyster species, P. maxima (silver-lip pearl oyster) and P. margaritifera (black-lip pearl oyster), were used to examine their influence on pearl quality and to further our understanding of the respective contribution host and donor oysters have in pearl formation. Here, host oysters were implanted with mantle tissue originating from either the same species (allograft) or the other species (xenograft) and pearl formation allowed to proceed for 14 months, where after pearls were harvested and nuclei retention and pearl quality traits (nacre deposition/weight, shape, colour, complexion and lustre) recorded. Results showed that xenografts did not significantly affect pearl sac formation and subsequent nuclei retention ( χ 2 = 5.64, df = 3, P > 0.05), but did influence pearl colour, complexion, shape, nacre deposition and nacre weight ( P < 0.05). Nacre deposition and weight were found to be higher in xenografts comprising of a P. maxima donor and P. margaritifera host, than in the reciprocal xenograft and allografts. Pearl colour and complexion were also strongly influenced by the donor oyster species used as xenografts, with P. maxima host oysters implanted with mantle from P. margaritifera producing generally black colour based pearls. Conversely, P. margaritifera hosts implanted with P. maxima mantle produced silver colour based pearls. This study demonstrates the potential of xenografts as a means to improve pearl quality traits such as pearl size, and highlights the role that donor oysters have in the realisation of pearl growth, colour and surface complexion.

Regeneration of excised mantle tissue by the silver-lip pearl oyster, Pinctada maxima (Jameson)

This study investigated the capacity for mantle regeneration in the pearl oyster Pinctada maxima. Oysters were anaesthetised with 2.5 mL L −1 prophylene phenoxetol prior to a piece of tissue (approximately 10 × 30 mm 2) being excised from the ventral region of the mantle. In the first experiment, 56 oysters with mean (±SD) dorso–ventral measurement (DVM) of 125.5 ± 8.9 mm had tissue excised from either the right mantle lobe, left mantle lobe or both mantle lobes. Following a further three month period in suspended culture, oyster survival was recorded and two oysters were selected arbitrarily from each group to be sacrificed for histological examination of healed mantle. In the second experiment 36 oysters with mean (±SD) DVM of 151.6 ± 13.4 mm were used for excision of the distal part of the ventral region of the left mantle lobe. Two oysters were sampled at 1, 3, 6, 12, 24, 36, 48, 72 and 120 h (5 days) after mantle excision, and then at 12, 24, 45, 72 and 90 d after mantle excision for histological and histochemical analysis of mantle regeneration. There was almost 100 percent survival in both experiments. Healing and regeneration of mantle tissue in oysters subject to excision from the left, right or both mantle lobes was evident, with regenerated mantle appearing similar to non-regenerated mantle. All external and internal components of non-regenerated mantle were present in regenerated mantle tissue. Epithelization signifying wound healing occurred within 36–72 h and was characterised by a reduced wound area, haemocyte infiltration and accumulation, and cell dedifferentiation. Within 48 h of mantle excision, the latero-ventral edges of the wound flexed dorsally and attached to the dorsal edge of the wound reducing the wound area. Between five and twelve days after excision, the distal part of the mantle had divided into three small lobes which developed into the outer, middle and inner mantle folds two weeks later. Ninety days after excision the mantle had completely regenerated with histological observations indicating no difference in epithelial structure or in other internal mantle accessories when compared to non-regenerated mantle. Shell material began to be secreted onto the shell by regenerating mantle twelve days after excision. Initially this occurred in a position dorsal to the non-injured mantle edge. However, forty-five days after mantle excision, regenerated mantle had extended ventrally to a position similar to that of non-injured mantle. Nacre deposition by regenerated mantle had now reached the same position ventrally as that of non-injured mantle indicating full acquisition of nacre secreting abilities by regenerated mantle.

Use of anaesthetics with the silver-lip pearl oyster, Pinctada maxima (Jameson)

Mortality, lower pearl retention and low pearl quality can be major problems in cultured pearl production. Anaesthetics may have a role in the pearl seeding process and this aspect was investigated in this study. Seven anaesthetic treatments, 3 mL L−1 2-phenoxyethanol, 500 mg L−1 and 1200 mg L−1 of benzocaine, 1.5 mL L−1 clove oil, 0.25 mL L−1 and 0.4 mL L−1 menthol liquid, and 2.5 mL L−1 propylene phenoxetol were assessed for their ability to relax the silver-lip pearl oyster, Pinctada maxima. Of the 27 oysters exposed to each treatment, the highest proportion of relaxed oysters (96.3, 88.9 and 88.9%) and the shortest exposure times required for anaesthesia (13.8±6.4, 10.5±7.9 and 15±7.1 min), were recorded for the treatments of 3 mL L−1 2-phenoxyethanol, 1200 mg L−1 of benzocaine, and 2.5 mL L−1 propylene phenoxetol, respectively. In contrast, none of the oysters exposed into 0.25 mL L−1 menthol liquid became relaxed and most oysters exposed into 1.5 mL L−1 clove oil died during the experiment. Oysters exposed to 3 mL L−1 2-phenoxyethanol and 1200 mg L−1 benzocaine remained relaxed for up to 30 min while the number of relaxed oysters exposed to 2.5 mL L−1 propylene phenoxetol decreased during that time. With the exception of oysters exposed to clove oil, all relaxed oysters recovered within 2 h of being placed back into seawater and there was close to 100% survival after one month.

Decreased genetic diversity and a reduced effective population size in cultured silver-lipped pearl oysters ( Pinctada maxima)

Before selection programmes for aquaculture species can commence, a fundamental knowledge of how the culture process affects genetic diversity is requisite. “South Sea” pearl production, through the culture of the silver-lipped pearl oyster, Pinctada maxima, stands to gain substantially from genetic selection. Aquaculture techniques for P. maxima have progressed vastly, to a point where the majority of current operations are based on hatchery-propagated stock; however, there has been no investigation on how the culture process is affecting the genetic diversity of this species. To address this deficiency, we investigated the genetic diversity and effective population sizes ( N e) in three wild and five hatchery-produced P. maxima populations. Using six microsatellite DNA markers, cultured populations exhibited low N e (3.5–9.2) and reduced allelic richness (29–44%) compared with their wild progenitors. Observed heterozygosities were not affected greatly, however, an increased mean pairwise genetic relatedness was observed in all cultured populations. The practice of mass spawning was identified as a major factor in the reduction of diversity, although diversity was not necessarily maintained when a more controlled spawning approach was utilised. Pedigree reconstructions revealed genetic diversity and N e is affected by large skews in full-sib family representations (up to 40% from a single family, in a cohort using 28 broodstock), and could be due to differential survival rates amongst communally reared families. In order to maximise future selective breeding efforts, further research should be directed towards identifying critical stages of the culture process in which genetic diversity is lost.

Family by environment interactions in shell size of 43-day old silver-lip pearl oyster ( Pinctada maxima), five families reared under different nursery conditions

To understand the influence the environment and associated genotype by environment interactions will exert on future silver-lip pearl oyster ( Pinctada maxima) selective breeding programs, this study assessed the relative performance in four shell growth traits of spat from five full-sib families, when spat were communally reared at different salinities (29, 34 and 40 ppt), food availability (high, medium and low), food quality (high, medium and low), and in a hatchery vs. ocean environment for 43 days. Rearing environment was found to influence growth expression, with significant differences evident when oysters were grown at different salinities in the ocean instead of hatchery, or when fed algae of differing nutritional quality. As indicated by MANOVA, family comparative growth performances were also altered when the environment changed, with significant environment by family interactions apparent in the food quality, food availability and hatchery vs. ocean rearing treatments. Changes in salinity, however, did not affect relevant family performances. These results indicate that growth and relative family performance in P. maxima may change dependent on local environmental conditions and that genotype by environment effects may need to be considered in breeding programs for this species.

Towards selective breeding of the silver-lip pearl oyster (Pinctada maxima): Understanding genotype by environment (G × E) interactions

Towards selective breeding of the silver-lip pearl oyster (Pinctada maxima): Understanding genotype by environment (G × E) interactions

TRANSPORT AND RECRUITMENT OF SILVER-LIP PEARL OYSTER LARVAE ON AUSTRALIA'S NORTH WEST SHELF

Abstract Silver-lip pearl oyster (Pinctada maxima) spat surveyed in the Eighty Mile Beach section of the North West Shelf have been used in conjunction with outputs from a particle dispersion model to identify likely spawning grounds. The dispersion model consisted of a 3-dimensional regional circulation model in which large numbers of individual particles were tracked over the period 1994 to 1999. From the settlement areas defined by the spat data, larvae were tracked back in time over their estimated pelagic phase of 24–31 days within the main spawning period of mid October to late December. The reverse calculation was also undertaken looking at larval dispersion from known broodstock populations. Results demonstrate that large tidal currents in the region move larvae back and forth across the shelf, whereas lower frequency currents influence their net transport. Whereas some model larvae traveled more than 60 km, most were transported less than 30 km. The model results suggest that spawning in the Eigh...

GROWTH, MORTALITY, RECRUITMENT AND SEX-RATIO IN WILD STOCKS OF SILVER-LIPPED PEARL OYSTER PINCTADA MAXIMA (JAMESON) (MOLLUSCA: PTERIIDAE), IN WESTERN AUSTRALIA

Abstract Growth, mortality, recruitment and sex-ratio of wild stocks of the silver-lipped pearl oyster Pinctada maxima were studied at sites spanning the geographic extent of the commercial fishery using mark-recapture experiments, recruitment cohort analysis and research surveys of stock abundance and reproductive status. Growth parameters (L∞, K) from the von Bertalanffy growth equation were estimated at 210 mm dorso-ventral measurement (DVM) (±16 mm SD) and 0.74 at the Lacepede Islands, L∞ of 199 mm DVM (±6 mm SD) and K of 0.79 on 80 Mile Beach, and L∞ of 194 mm (±6 mm SD), and K of 0.72 at Exmouth Gulf respectively. Estimates of natural mortality (M) by tagging were very low (0.02–0.03), compared with catch-curve analysis, which estimated M to be between 0.1 in deeper (30–34 m) populations and 0.18 in shallow (9–12 m) populations. Settled P. maxima spat (0 + and 1 + age classes) on adult shell were quantified (e.g., 1,317 spat found on 119,000 shell in 2003) to obtain an annual recruitment index, whic...

Excavating sponges that are destructive to farmed pearl oysters in Western and Northern Australia

Species of the family Clionaidae (Porifera: Demospongiae) that excavate shell of the silver-lip pearl oyster, Pinctada maxima, in north Western and Northern Australia are described. Two species belong to the genus Cliona and one species to the closely related genus Pione. Cliona orientalis has only recently been reported from Australia in living and dead coral on the Great Barrier Reef, and this is the first report of this species from north Western and Northern Australia. Cliona dissimilis is reported from Australia for the first time. Pione velans was first described from Shark Bay, Western Australia and this study extends its distribution from Albany, south Western Australia to Port Bremer in the Northern Territory. The most common species found was C. dissimilis. Pione velans and C. orientalis were also present, although the latter species was rare. Cliona dissimilis and P. velans were found to be sexually reproductive in some shells with specimens of C. dissimilis with oocytes in May and P. velans in September 1999. Egg development was synchronous, indicating that the sponges were oviparous and would broadcast gametes in a spawning event.

Effects of mesh covers on the growth and survival of silver-lip pearl oyster ( Pinctada maxima, Jameson) spat

Spat of the silver-lip (or gold-lip) pearl oyster, Pinctada maxima, were re-settled onto PVC slats at a mean density of 340 per 100 cm 2. Spat had a mean (±s.e.) dorso-ventral shell height and antero-posterior shell length of 1.2±0.3-mm and 1.8±0.5-mm, respectively. The PVC slats were either left exposed (control) or covered with a mesh sleeve of varying aperture sizes (0.75, 1.5 or 3.0-mm) before being transferred to an ocean-based suspended nursery culture system. After two weeks of nursery culture, there was no significant difference ( P>0.05) among the number of spat retained on the covered slats; however, all covered slats had significantly greater ( P<0.001) spat retention than the control which had fewer than 1 spat per 100 cm 2. Some of the spat in the control treatment may have been eaten by box fish (Ostraciidae) and file fish (Monacanthidae) which were observed pecking at the exposed PVC slats. Shell height and shell length increased significantly ( P<0.05) with each increase in mesh size. The remaining spat on the control slats were smaller than the mean size of the spat at the start of the trial although this difference was not significant ( P>0.05). This probably resulted from fish and other predators preferentially attacking the larger individuals. There was no advantage in using sleeves with a mesh size small enough to retain dislodged spat. The majority of dislodged spat in the 0.75-mm and 1.5-mm mesh sleeves perished when they fell into the corners of the sleeve whereas most dislodged individuals were small enough to fall through the 3.0-mm mesh sleeve. A 3.0-mm mesh is appropriate to house spat of the size used in this study. Smaller mesh sizes, while not affecting survival, fouled more rapidly and resulted in reduced spat growth.

Assessment of artificial substrates for collection of hatchery-reared silver-lip pearl oyster ( Pinctada maxima, Jameson) spat

This paper reports on three experiments in which artificial substrates were assessed for the collection of hatchery-reared silver-lip (or gold-lip) pearl oyster, Pinctada maxima (Jameson), spat. In the first experiment, pediveliger larvae were settled onto collectors made from a variety of materials: curved PVC slats; polypropylene rope; a combination of PVC slats and polypropylene rope; and monofilament nylon. After 37 days, the rope and the combined PVC slat and rope collectors had significantly higher numbers of spat ( P<0.05) than either nylon or PVC slat collectors. In a second experiment, PVC slat collectors were placed in a larval settlement tank in either a horizontal or vertical orientation. Significantly greater numbers of spat ( P<0.001) were observed on horizontally positioned PVC slat collectors than on collectors positioned vertically. Regardless of orientation, the concave surface of PVC slats had significantly higher ( P<0.001) numbers of spat than the convex surface. In the third experiment, collection of P. maxima spat was compared between PVC slats with or without an epifloral biofilm. Significantly more ( P<0.001) spat attached to PVC slats with a biofilm than clean PVC slats. These results indicate that the choice of collector material, the surface orientation of collectors and method of collector preparation can optimise the collection of hatchery-reared P. maxima spat.

Inducing detachment of silver-lip pearl oyster ( Pinctada maxima, Jameson) spat from collectors

A number of stress factors were assessed for their potential to induce detachment of silver-lip (or gold-lip) pearl oyster ( Pinctada maxima, Jameson) spat from spat collectors. The factors assessed were: increased salinity to 40 parts per thousand (ppt) or 45 ppt, reduced salinity to 30 ppt or 25 ppt, raised (to pH 10) and reduced (to pH 4) pH and exposure to air. All treatments promoted significantly greater ( P < 0.001) percent spat detachment than the control treatment of ‘normal’ sea water (34 ppt, pH 8.0). The pH 10 treatment resulted in heavy mortality (86%) after 1 h and was abandoned. The greatest percentage of detached spat (92.3 ± 0.6%, mean ± s.e.) resulted after 1 h exposure to hypersaline sea water at 45 ppt, this was significantly greater ( P < 0.05) than for any other treatment. The next best treatment was pH 4, which resulted in 85.6 ± 2.3% detached spat after 1 h. Exposure to the treatments beyond 1 h, except in the case of exposure to air, did not yield significant increases ( P > 0.05) in the proportion of detached spat. Spat that had detached in the treatment baths within the first hour began to re-attach during the second hour. With the exception of the pH 10 and air exposure treatments, detached spat in all treatments had firmly re-attached and had apparently adapted to the new environmental conditions after 24 h. Survival of spat left exposed to these treatments for 24 h was 100% as was the survival of spat exposed to air for up to 6 h. No mortality was recorded for any treatment 24 h after the spat were returned to control sea water.

Notes on Animals Attached to the Shells of the Silver-Lip Pearl Oyster, Pinctada maxima (JAMESON), Collected from the “East” Fishing Ground of the Aratura Sea

Notes on Animals Attached to the Shells of the Silver-Lip Pearl Oyster, Pinctada maxima (JAMESON), Collected from the “East” Fishing Ground of the Aratura Sea