37 research outputs found
Mise en place d'un Réseau de Veille Zoosanitaire des hußtres perliÚres Pinctada margaritifera en Polynésie Française
Lâimportance socio-Ă©conomique de lâactivitĂ© perliĂšre justifie que le Service de la Perliculture mette en place un rĂ©seau de surveillance pathologique de lâhuĂźtre perliĂšre Pinctada margaritifera en PolynĂ©sie française. Les objectifs de ce rĂ©seau sont de prĂ©venir lâintroduction ou lâapparition dâagents infectieux, de prĂ©venir leur propagation Ă lâintĂ©rieur dâune zone dâĂ©levage, dâĂ©tudier les moyens de limiter leur impact, de surveiller leur Ă©volution et enfin de garantir les Ă©changes entre les zones dâĂ©levage.
Cette premiĂšre annĂ©e a permis dâĂ©laborer le schĂ©ma de fonctionnement du rĂ©seau et de vĂ©rifier sa faisabilitĂ©. Cinq zones de prĂ©lĂšvements ont Ă©tĂ© dĂ©finies en fonction de critĂšres dâaccessibilitĂ© Ă la zone et de facilitĂ© dâacheminement des Ă©chantillons, de lâimportance du collectage, de la densitĂ© des Ă©levages et de la gĂ©omorphologie. Il sâagit de Makemo, Fakarava, Tahaa, Takaroa et Rikitea. Par zones, deux Ă trois sites sont suivis. Ainsi, pour 2003, 406 huĂźtres, P. margaritifera, 21 P. maculata (pipi), 11 S. cucullata (kapi kapi) et 1 Chama sp. ont Ă©tĂ© analysĂ©s. Les analyses histologiques effectuĂ©es ne font apparaĂźtre aucun agent pathogĂšne Ă dĂ©claration obligatoire Ă lâOffice International des Epizooties. Les huĂźtres dâĂ©levage examinĂ©es prĂ©sentent un degrĂ© plus ou moins important dâatteinte parasitaire par des sporozoaires de type grĂ©garine et des parasites de type Rickettsia-like. De mĂȘme, lâespĂšce P. maculata (pipi) est affectĂ©e par des grĂ©garines. Des zones dâenkystement de mĂ©tazoaires ont Ă©tĂ© Ă©galement observĂ©es chez P. margaritifera et Saccostrea cucullata.
Ces parasites ne sont pas associĂ©s Ă des maladies. Toutefois leur prĂ©sence entraĂźne des dĂ©sordres tissulaires plus ou moins importants qui peuvent rendre lâhuĂźtre plus sensible au stress de la greffe. Dans ces conditions il paraĂźt utile dâeffectuer un nombre plus Ă©levĂ© dâanalyse afin de mieux dĂ©crire ce phĂ©nomĂšne et dâapprofondir les investigations dans les Ăźles les plus sensibles.
Un schĂ©ma dâorganisation Ă mettre en place en cas dâĂ©pisodes de mortalitĂ© ou de morbiditĂ© dĂ©clarĂ©es est proposĂ©. Il est en effet important de dĂ©finir dĂšs aujourdâhui la procĂ©dure afin de mobiliser les compĂ©tences et les informations le plus rapidement possible. Les informations recueillies lors de ces situations de crise apporteront les Ă©lĂ©ments nĂ©cessaires Ă la prise de dĂ©cision en matiĂšre de rĂ©glementation et/ou dâinformations auprĂšs des services compĂ©tents du territoire et des professionnels
Bilan 2005-2006 du Réseau de Veille Zoosanitaire des hußtres perliÚres, Pinctada margaritifera, en Polynésie française
En 2005 et 2006, un total de 1333 analyses réparties en 1109 hußtres perliÚres, P. margaritifera, 93 pipi, P. maculata, 27 chama, Chamidae sp, 46 kapi kapi, Saccostrea cucullata et 58 Isognomon sp. ont été effectuées dans le cadre du REseau de PAthologie des hußtres perliÚres (REPANUI). Les analyses histologiques ont révélé comme les années précédentes la présence de sporozoaires de type grégarine, des parasites de type Rickettsien, des kystes de cestodes (Tylocephalum sp.). Une infection par des vers trématodes a été détectée chez S. cucullata.
Depuis la mise en place de cette surveillance active en 2003, aucun agent pathogĂšne Ă dĂ©claration obligatoire de la liste de lâOffice International des Epizooties (OIE) nâa Ă©tĂ© diagnostiquĂ©, confirmant le bon Ă©tat sanitaire des mollusques bivalves analysĂ©s en PolynĂ©sie française. En outre, aucun Ă©pisode de mortalitĂ© ni de morbiditĂ© anormale nâa Ă©tĂ© relatĂ© depuis le dĂ©but de la mise en place de ce rĂ©seau.
Lâeffort analytique consenti depuis 2003 a permis de dĂ©terminer les taux de prĂ©valence, dâinfection, la rĂ©partition gĂ©ographique et temporelle des principaux organismes dĂ©crits chez P. margaritifera (protozoaires et mĂ©tazoaires). Toutes ces analyses ont permis de dĂ©velopper une base de donnĂ©es informatiques et une «bibliothĂšque » de lames histologiques de rĂ©fĂ©rence des tissus sains et parasitĂ©s des mollusques bivalves en PolynĂ©sie française. Ces donnĂ©es permettront de mobiliser le plus rapidement possible toutes les informations nĂ©cessaires pouvant aider Ă la gestion de situations de crise liĂ©es Ă des mortalitĂ©s anormales et/ou Ă la dĂ©tection de nouveaux agents pathogĂšnes
Characterization of two new genes implicated in mineralization process of Pinctada margaritifera
A transplant is a complex surgical procedure performed to obtain a pearl after about 12 to 18 months. One of the key steps in this procedure is the transfer of the graft (piece of mantle) from the donor oyster. A functional relationship exists between the coating nature of the pearl and the cellular structure of the pearl bag portion of the graft. We have identified two genetic markers of biomineralisation in Pinctada margaritifera, the pearl oyster: Perline and Calcine, responsible for secretion of aragonite and calcite, respectively. After isolating and sequencing a portion of each of these genes, we verified the specificity of these sequences using molecular methods (RT-PCR, in situ hybridisation) and biocomputing methods (alignments, phylogenetic trees, amino-acid composition). We have attempted to make a graft cartography to distinguish zones coding for expression of Perline and Calcine mRNA. The goal of this research is to define precisely the zone for selection of a graft (in a non empiric way) to achieve a desired balance between Perline and Calcine
Bilan final 2004-2007 du Réseau de Veille Zoosanitaire REPANUI des hußtres perliÚres Pinctada margaritifera en Polynésie francaise
De nombreuses pathologies affectent les mollusques, dont les huĂźtres perliĂšres. Celles-ci peuvent ĂȘtre sensibles Ă des maladies, ce qui peut entraĂźner parfois de fortes mortalitĂ©s au sein dâune population. La prĂ©sence de certains agents pathogĂšnes dans la rĂ©gion Asie-Pacifique ainsi que les fortes mortalitĂ©s dans les annĂ©es 1985 sur le cheptel de Pinctada margaritifera en PolynĂ©sie française, permet de se rendre compte de la vulnĂ©rabilitĂ© de la filiĂšre perlicole.
De part lâimportance socio-Ă©conomique de la perliculture en PolynĂ©sie française, le Service de la Perliculture, en collaboration avec lâIfremer de Tahiti, a mis en place en 2003 un rĂ©seau de surveillance Ă©pidĂ©miologique des pathologies de lâhuĂźtre perliĂšre P. margaritifera (REPANUI). AprĂšs cinq annĂ©es de fonctionnement, le rĂ©seau a permis de dĂ©terminer les organismes prĂ©sents sur le territoire. Un bilan des rĂ©sultats obtenus par le REPANUI est proposĂ© afin dâĂ©valuer la situation Ă©pidĂ©miologique actuelle. Une validation du fonctionnement du rĂ©seau est Ă©galement proposĂ© (CES dâĂ©pidĂ©miologie de lâEcole VĂ©tĂ©rinaire de Maison Alfort) avant le transfert de lâanimation et de la gestion opĂ©rationnelle de REPANUI le 26 mai 2008.
Le rĂ©seau a permis dâeffectuer 2797 analyses dâhuĂźtre perliĂšres et 493 analyses dâautres mollusques sauvages. Les analyses histologiques effectuĂ©es dans le cadre du REPANUI ont permis de dĂ©terminer les agents pathogĂšnes prĂ©sents sur le Territoire de PolynĂ©sie française : grĂ©garines, rickettsie-like, kyste de Tylocephalum. Des tendances ont Ă©tĂ© dĂ©gagĂ©es parmi les agents pathogĂšnes prĂ©sents :
- les parasites de type grĂ©garines sont prĂ©sents avec une frĂ©quence de dĂ©tection Ă©levĂ©e de lâordre de 70 Ă 90 %;
- les rickettsie-likes prĂ©sentent une frĂ©quence de dĂ©tection de lâordre de 5 Ă 10 % ;
- les kystes de Tylocephalum correspondent Ă une frĂ©quence de dĂ©tection de lâordre de 5 Ă 10 %.
Depuis la mise en place de ce rĂ©seau, aucun agent infectieux Ă dĂ©claration obligatoire de la liste de lâorganisation mondiale de la santĂ© animale (OIE) nâa pus ĂȘtre mis en Ă©vidence. Ceci confirme le statut indemne de la PolynĂ©sie française par rapport aux pathologies des huĂźtres perliĂšres. Seule une dĂ©claration de mortalitĂ©, dĂ©mentie ensuite, a Ă©tĂ© enregistrĂ©e au Service de la Perliculture en 2008. Ces rĂ©sultats seront Ă confirmer dans les annĂ©es Ă venir
A histological examination of grafting success in pearl oyster
Pearl oyster grafting is a complex surgical operation that should lead to pearl formation after approximately eighteen months. Although this technique has been used for many years in French Polynesia, the grafting process is still not standardised. While studies have been carried out in order to improve graft performance and yield, these remain highly variable due to post-grafting mortality, nucleus rejection and unreliable pearl quality, all of which constrain pearl farm profitability. The present study uses histological analysis to monitor oysters that either rejected or retained their nuclei. Both groups of oysters are compared in terms of evolution of the graft, which could influence retention, and the development of a pearl sac in cases where grafting was successful. Data show that rejection phenomena are linked to a number of causes, notably an inflammatory reaction in the âreceivingâ oyster, the presence of numerous tissue lesions and the
quality of the grafted tissue. These results suggest that study is needed on the different concomitant elements of the grafting process: the graft âdonorâ oysters, the nucleus and the âreceivingâ oyster and their interactions
Biofouling development and its effect on growth and reproduction of the farmed pearl oyster Pinctada margaritifera
In bivalve aquaculture, dominant fouling organisms are filter feeders which can compete for food with reared bivalves, sometimes causing mortality or reducing their growth rate. This study investigated the effect of biofouling on the farmed pearl oyster Pinctada margaritifera in two lagoons of French Polynesia. Survival, growth and reproduction of 2 year-old pearl oysters were monitored with regular sampling schedules, from the initial stage of colonization up to 20 months of biofouling accumulation. Control groups of pearl oysters were kept free of biofouling as is the current practice in pearl farms. After more than a year of monitoring, no significant difference was recorded in shell growth rate between pearl oysters reared with epibionts and the control group of pearl oysters, at both sites. Mean annual shell growth rate (height) was 30.5 ± 9.2 mm in Tahiti and 24.8 ± 7.7 mm in Mangareva. Neither the survival nor the reproduction indices were negatively affected by biofouling. In Mangareva, where biofouling development was quantified during 1 year, the rate of colonization appeared to be high during the first 3 months before slowing down. These results raise questions about the necessity of removing biofouling at this stage of pearl oyster production (i.e. before grafting)
Molecular Signatures Discriminating the Male and the Female Sexual Pathways in the Pearl Oyster Pinctada margaritifera
The genomics of economically important marine bivalves is studied to provide better understanding of the molecular mechanisms underlying their different reproductive strategies. The recently available gonad transcriptome of the black-lip pearl oyster Pinctada margaritifera is a novel and powerful resource to study these mechanisms in marine mollusks displaying hermaphroditic features. In this study, RNAseq quantification data of the P. margaritifera gonad transcriptome were analyzed to identify candidate genes in histologically-characterized gonad samples to provide molecular signatures of the female and male sexual pathway in this pearl oyster. Based on the RNAseq data set, stringent expression analysis identified 1,937 contigs that were differentially expressed between the gonad histological categories. From the hierarchical clustering analysis, a new reproduction model is proposed, based on a dual histo-molecular analytical approach. Nine candidate genes were identified as markers of the sexual pathway: 7 for the female pathway and 2 for the male one. Their mRNA levels were assayed by real-time PCR on a new set of gonadic samples. A clustering method revealed four principal expression patterns based on the relative gene expression ratio. A multivariate regression tree realized on these new samples and validated on the previously analyzed RNAseq samples showed that the sexual pathway of P. margaritifera can be predicted by a 3-gene-pair expression ratio model of 4 different genes: pmarg-43476, pmarg-foxl2, pmarg-54338 and pmarg-fem1-like. This 3-gene-pair expression ratio model strongly suggests only the implication of pmarg-foxl2 and pmarg-fem1-like in the sex inversion of P. margaritifera. This work provides the first histo-molecular model of P. margaritifera reproduction and a gene expression signature of its sexual pathway discriminating the male and female pathways. These represent useful tools for understanding and studying sex inversion, sex differentiation and sex determinism in this species and other related species for aquaculture purposes such as genetic selection programs
Identifying Robust Proxies of Gonad Maturation for the Protandrous Hermaphrodite Tridacna maxima (Röding, 1798, Bivalvia) from Individual to Population Scale
Monitoring gonadmaturation for protandrous and functional hermaphrodite species such as the giant clamTridacna maxima is difficult due to the juxtaposition and relative proportion ofmale and female tissues in the gonad [gonadal sex ratio (GSR)]. Here, the relevance of the widely used gonadosomatic index (GSI) as proxy of giant clam gonad maturation is tested with a large dataset (n = 265). Gonadosomatic index is compared with other indices, namely the proportion of the male part harboring spermatozoids, the proportion of empty oocyte follicles, the mean oocyte diameter, and the oocyte elongation. At gonad scale, high index variability highlighted partial spawning. At individual scale, male and female maturation proxies were contrasted, showing either asynchronous emissions of male and female gametes or contrasted spermatogenesis and oogenesis duration. The GSI was mostly driven by the number and diameter of oocytes and therefore it is recommended here as primary proxy for female maturity. Except for the oocyte elongation, all indices were affected by the GSR, which ruled out drawing conclusions at population scale. These results highlight the need for maturation stage proxies that are optimized for functional hermaphrodite species