The latest information on pearl farming in Tahiti

The sterility and faster growth of triploid individuals, commonly used in aquaculture, present a major advantage for the pearl industry. Their use could shorten the grow-out cycle and facilitate grafting operations.

Experiments aimed at producing triploid oysters using cytochalasin B were carried out at the hatchery of the Pearl Farming Service on the atoll of Rangiroa, as well as at IFREMER’s aquaculture station in Vairao (Tahiti).

Ploidy Analysis and Larval Rearing

Zygotes and embryos, stained with Hoechst 33258, were observed under epifluorescence microscopy to determine their ploidy. The larvae were reared using techniques developed at the Rangiroa hatchery. For the settlement phase, artificial collectors were submerged in tanks containing the oyster larvae.

Ten days later, the collectors containing the spat were suspended from a longline in the lagoon for the grow-out phase, which lasts from three months to one year. This step made it possible to study the chronology of embryonic development.

On average (n = 17), the expulsion of the first polar body occurred 12.2 minutes after fertilization. The second polar body was expelled after 27.3 minutes, and the two-cell stage appeared after 55.5 minutes.

Results Obtained

In 2003, the experiments aimed at retaining the second polar body produced 95% triploid embryos before the first cell division. The survival rate at the straight-hinge larval stage reached 65% in the diploid control larvae.

Up to 40% of the larvae displayed morphological abnormalities, but these had no significant effect on growth or survival rates.

After one year, gill samples were analyzed to confirm ploidy. Result: 98% of the treated individuals were triploid, with only two juveniles out of 130 remaining diploid.

The mean shell diameter was 59.9 mm for triploid oysters and 63.9 mm for diploid controls, likely due to the higher density of triploid spat in the collectors.

Outlook

The growth and gonadal development observed after two months of treatment in the hatchery are detailed in this article. These results confirm the potential of triploid oysters to improve productivity and efficiency in Polynesian pearl farming.

The value of a pearl increases exponentially with its quality. Among the evaluation criteria, shape plays a decisive role: perfectly round pearls are by far the most sought after and command the highest prices.

Thus, the primary objective of any pearl farmer is to increase the percentage of round pearls in their production. To determine whether genetic lineage influences pearl quality, two groups of Pinctada maxima were monitored over four years, from hatchery to harvest.

Two Groups, Two Origins

Group A came from the spawning of gold-lipped oysters selected in the Aru Islands, southeast of Indonesia.

Group B consisted of oysters bred from individuals originating in the Raja Ampat Islands, northeast of Indonesia, all of which had gold- or yellow-lipped nacre.

Both groups were raised under identical conditions at a commercial pearl farm located in Alyui Bay, West Papua.

Results: Lineage Makes a Difference

At harvest, researchers observed significant quality differences, particularly regarding shape.

Oysters from Group A produced a higher percentage of round pearls than those from Group B, demonstrating that lineage plays an important role in the final quality of pearls.

Toward More Efficient Selective Breeding

These results suggest that selective breeding could become a key tool for improving the quality and, consequently, the value of the pearls produced.