Emmanuel Goyard

Pearl Formation: Persistence of the Graft During the Entire Process of Biomineralization

Most bivalves species of the genus Pinctada are well known throughout the world for production of white or black pearls of high commercial value. For cultured pearl production, a mantle allograft from a donor is implanted into the gonad of a recipient oyster, together with a small inorganic bead. Because of the dedifferentiation of cells during the first steps of the host oyster’s immunological reaction, so far the fate of the graft and its exact role in the process of pearl formation could not be determined via classical histological methods. Here we report the first molecular evidence of the resilience of the graft in the recipient organism by showing that cells containing genome from the donor are still present at the end of pearl formation. These results suggest the existence of a unique biological cooperation leading to the successful biomineralization process of nacreous secretion in pearl formation.

Selection for better growth of Penaeus stylirostris in Tahiti and New Caledonia

Abstract The penaeid shrimp, Penaeus stylirostris , has been domesticated in French Polynesia and New Caledonia for 20 years and was used in an experimental mass selection for better growth. The population under selection was graded once or twice each generation, which induced a selection rate fluctuating between 4% and 18% from 1 year to the next. At each generation, 24 to 32 individuals were used as parents (Ne=21–32) in the selected line and in the control line. The injection of colored elastomer in the two populations allowed an assessment of the genetic progress in earthen rearing ponds. The fifth generation demonstrated an increase of growth rate of 21% when compared to the nonselected control line. The optimization of the selection schemes and their integration into the production hatcheries is discussed with a special focus on the optimization of the age of grading.

A relationship between antimicrobial peptide gene expression and capacity of a selected shrimp line to survive a Vibrio infection

Understanding of antimicrobial defence mechanisms of penaeid shrimp should help in the design of efficient strategies for the management and disease control in aquaculture. In this study, we have specifically analysed the expression in circulating hemocytes of antimicrobial peptides (AMPs) encoding genes, such as PEN2 and PEN3, ALF, crustin, lysozyme and a putative cysteine-rich peptide. We evidenced a relationship between the level of expression of some AMPs and the successful response of the shrimp, Litopenaeus stylirostris, to circumvent a pathogenic Vibrio penaeicida infection. Additionally, significant differences in some AMP transcript amounts are evidenced between control, non-selected shrimp line and the third generation breeding of shrimp selected for their survival to natural V. penaeicida infections. On the basis of these results, it will now be of great interest to determine if these AMPs are directly involved in the resistance of shrimp to infection or if they only reflect other acquired defence mechanisms which can confer a resistance.

Spatio‐temporal variation in the genetic composition of wild populations of pearl oyster (Pinctada margaritifera cumingii) in French Polynesia following 10 years of juvenile translocation

The genetic impact of the cultural practice of spat collection and translocation between genetically distinct stocks of black‐lipped pearl oyster, Pinctada margaritifera cumingii, was studied by comparing samples collected in the 1980s and 2000s from seven atolls in French Polynesia. An amova revealed homogenization of the previously genetically distinct wild stocks of Tuamotu‐Gambier and Society archipelagos (the indices of genetic differentiation among archipelagos and among populations within archipelagos, respectively, ΦCT and ΦST, decreased from 0.032* and 0.025*, respectively, to 0.006NS and 0.007NS). These results suggest high success of spontaneous reproduction in farms, probably due to the very high density of cultivated pearl oysters, and underline the importance of genetic monitoring of future hatchery produced stocks.

Spat collection of the pearl oyster (Pinctada margaritifera cumingii) in French Polynesia: an evaluation of the potential impact on genetic variability of wild and farmed populations after 20 years of commercial exploitation

Pearl production, based on the aquaculture of the blacklipped pearl oyster Pinctada margaritifera, is an essential economic activity in French Polynesia. Production relies almost exclusively on the collection of wild spat, which makes the activity very dependent on natural resources. A good knowledge of these resources is thus essential for the rational management of farmed and wild populations. In this study, we analysed the structure of genetic variability, in wild and farmed populations distributed on four atolls from the Tuamotu–Gambier archipelago using four anonymous nuclear loci. No genetic difference was observed among samples from wild populations collected from Northern Tuamotu to Southern Gambier. This suggests that large-scale dispersal, either due to the absence of barriers to natural larval migration, or to the transport of collected spat for pearl production. No significant differences were found between wild and adjacent farmed populations for the number of alleles and observed heterozygosity, which supports the conclusion

Recent improvements in broodstock management and larviculture in marine species in Polynesia and New Caledonia: genetic and health approaches

Abstract Aquaculture production in French Polynesia and New Caledonia relies upon domesticated broodstock of two introduced species (the shrimp Litopenaeus stylirostris , and the fish Lates calcarifer ) and on natural stock of the local pearl oyster Pinctada margaritifera . For L. stylirostris , refrigeration of shrimp sperm lowers the sanitary risk linked to the re-introduction of variability in Tahiti that is proved necessary by microsatellite markers. They also allow paternity controls that will improve future genetic management. Selective breeding programs for shrimp are underway in Tahiti and under assessment at pilot scale in New Caledonia. Conservation strategies are under elaboration for local populations of P. margaritifera that have been proven genetically differentiated. The recent development of pearl oyster hatcheries is the first step towards genetic improvement of this species. Thanks to geographical isolation and sanitary regulations, French Polynesia and New Caledonia are not affected by the viral outbreaks affecting shrimp elsewhere in the world (e.g., white spot and Taura syndrome viruses) and the pearl oyster in Japan (Akoya virus). Furthermore, a zoosanitary surveillance network of pearl oyster stocks is coming up in order to detect the emergence of any pathogen. Recently, alternative methods for antibiotherapy in shrimp larval rearing have been tested using probiotic bacteria, and could find an application in pearl oyster larval rearing.