Evaluation des conséquences d'une situation hypoxique simulée sur la Capacité Osmorégulatrice des crevettes d'élevage, Penaeus stylirostris et Penaeus vannamei

Les résultats exposés dans ce rapport apportent des informations sur la Capacité Osmorégulatrice des crevettes d'élevage, Penaeus stylirostris et P. vannamei, face à un abaissement de l'oxygénation ambiante. Ces résultats s'appliquent à des juvéniles placés dans des conditions optimum en laboratoire mais à niveau métabolique bas : animaux à jeun, en stade d' intermue C, adaptés après dissipation du stress induit par la pêche et le transfert dans un nouvel environnement. Les mesures ont confirmé que les crevettes présentent une zone d'indépendance osmorégulatrice au-dessus de 3 mg O2.11 et· une zone de dépendance osmorégulatrice qui commence au-dessous de cette valeur. Ces résultats vont également dans le sens de ceux obtenus sur les tests de croissance et de survie (Aquacop, 1988) qui ont montré qu'une influence s'exerçait sur les gains de poids et la survie au-dessous de la même valeur. Au total, les juvéniles de crevettes de P. stylirostris et de P. vannamei présentent une bonne tolérance à l'hypoxie ambiante, que celle-ci résulte d'une exposition accidentelle de courte durée ou bien d'un traitement à longue durée qui semble par ailleurs la renforcer. Les résultats de croissance obtenus à long terme chez P.stylirostris sur la capacité osmorégulatrice et la croissance à une concentration moyenne de 2 mg O2.1-1 semblent repousser au-dessous de 3 mg O2.1.1  la limite adaptative des crevettes à l' hypoxie.

Rapport de la mission effectuée du 12 au 19/12/97en Nouvelle-Calédonie : - Ecophysiologie et Pathologie

Ecophysiologie L'outil Capacité Osmorégulatrice (CO) mis au point ces dernières années est devenue un moyen performant et largement exploité en routine dans nos programmes de recherche en environnement, en pathologie-immunologie, en génétique et en physiologie de la nutrition. La mise en oeuvre de cet outil nous a permis de répondre à un certain nombre de questions posées dans le cadre de nos objectifs de recherche. Il s'agissait dans un deuxième temps d'éprouver et d'adapter cet outil à des études in situ (dans les bassins d'élevages). C'est dans ce cadre qu'une action a été menée en Nouvelle-Calédonie avec nos collègues de la SASV. En Nouvelle-Calédonie, la chute de température préside à une dégradation du milieu et des conditions d'élevage et provoquerait de plus une diminution de la résistance immunologique des crevettes. Cette diminution déboucherait sur le syndrôme 93. L'effort de recherche de l'équipe Ecophysiologie en appui à la Nouvelle-Calédonie s'inscrit dans cette hypothèse. Au cours de cette mission, par la mesure de la CO des animaux en liberté dans les bassins, il a été montré que ceux-ci subissent un stress significatif lorsqu'ils sont exposés à un milieu défavorable en contact avec un sédiment réduit. Au vu de nos résultats obtenus in situ nous envisageons d'appliquer à terme l'outil CO dans le suivi de l'état physiologique de l'ensemble des crevettes du bassin. Une telle application apporterait aux producteurs calédoniens un outil supplémentaire d'aide à la décision dans la conduite de leurs élevages. Pathologie Un diagnostic de V. penaeicida, bactérie pathogène impliquée dans le Syndrôme 93 en NouvelleCalédonie, a récemment été mis au point au COP à Tahiti, utilisant la technique d'amplification en chaîne par la polymérase (PCR). Cette technique a été transférée avec succès en Nouvelle-Calédonie lors de cette mission, et ceci permet donc le lancement d'une vaste enquête épidémiologique qui se déroulera sur l'année 98. Des prélèvements d'hémolymphe et d'eau pourront être traités selon cette méthode ainsi probablement que des échantillons de boue de bassins nécessitant cependant quelques recherches complémentaires de mise au point du test sur ce type de prélèvements

Expériences préliminaires sur le conditionnement de géniteurs d'huÎtres perlières, Pincfada margarififera. Rapport final de la Convention N° 40440 Service de la Perliculture - Ifremer

En Polynésie française, la perliculture s'est développée à partir de naissain de captage. Les transferts de juvéniles entre les îles ont conduit à une certaine uniformisation des populations mais l'huître perlière reste essentiellement un animal sauvage (Arnaud et al. ,2003). Une des voies d'amélioration de la qualité des perles et de la rentabilité de la perliculture repose sur la sélection d'individus intéressants et/ou plus performants en particulier comme donneurs de greffons (couleur). L'étape qui consiste à multiplier les animaux sélectionnés passe nécessairement par le contrôle de la reproduction. Les travaux menés dans le cadre de précédentes conventions sur la triploïdisation, la cryoconservation et la maturation ovocytaire (Te Reko Parau N°16 et 17) montrent l'importance décisive de l'état de maturité des reproducteurs pour toutes les opérations de croisements dirigés. Il n'est pas possible de sélectionner des individus intéressants ou de préserver efficacement le patrimoine génétique de l'espèce sans un contrôle efficace de la gamétogenèse et du développement gonadique en laboratoire. A titre d'exemple, au cours de l'année 2004, 33 essais de déclenchement d'émission de gamètes ont été réalisés au COP sur des animaux élevés dans le lagon de Vairao. Ils ont concerné 1641 individus au total. Sept de ces essais se sont révélés totalement infructueux, seuls 41 individus ont émis des ovocytes, 274 du sperme. Le conditionnement des reproducteurs doit amener simultanément à maturité la plus grande partie de la population avec une production de gamète

Low energy cost for cultured pearl formation in grafted chimeric Pinctada margaritifera

The pearl oyster is one of the rare animal models that support two distinct genomes,  through the surgical graft process operated for culture pearl production. This grafted  organism is assimilated to a chimera whose physiological functioning remains poorly known.  The question of the energy expenditure comparison between chimera and non-chimera  animals arises. To answer this question, grafted and non-grafted pearl oysters were  evaluated for their energetic needs by the indirect calorimetry method. This method made it  possible to measure the energy expenditure based on the respiration rate (RR)  measurement, reflecting the basal metabolism. The results showed that the RR values for  grafted and non-grafted pearl oysters were not significantly different (p < 0.05). The  estimated cost of pearl calcification including CaCO3 and proteins synthesis was 0.237 ±  0.064 J h-1, representing 0.64 % of the total energy expenditure of grafted pearl oysters. This  study made it possible, for the first time, to see the energy cost of cultured pearl formation  in P. margaritifera and the little impact in the energetic metabolism of the chimera  organism

Physiological responses of female and male black-lip pearl oysters (Pinctada margaritifera) to different temperatures and concentrations of food

This study was designed to measure responses of four-year-old black-lip pearl oysters (Pinctada margaritifera) to different temperatures and food concentrations and to identify the energy requirements of each sex. Oysters were fed a monospecific microalgal diet of Isochrysis affinis galbana (T-iso). Measurements of oxygen consumption and ingestion rates were carried out at 24 degrees C and 27 degrees C and at two algal (T-iso) concentrations: 5000 and 30 000 cell ml(-1). Glycogen content in adductor muscle, absorption efficiency and scope for growth were also estimated. Females and males responded differently to environmental factors, with food level being the most influential parameter. Oxygen consumption and absorption efficiency were significantly higher in females than in males, but males had significantly higher glycogen content than females. At high food concentration, glycogen content, ingestion rate, oxygen consumption, and scope for growth were significantly higher than at the low food concentration. Only absorption efficiency was significantly higher at the low food concentration. Oxygen consumption was significantly higher at 27 degrees C than at 24 degrees C. These results indicate that females and males have different bioenergetic functioning and that energy demands for reproduction are higher in females

Microplastics Affect Energy Balance and Gametogenesis in the Pearl Oyster Pinctada margaritifera

Plastic pollution in the environment is increasing at global scale. Microplastics (MP) are derived from degradation of larger plastic items or directly produced in microparticles form (<5 mm). Plastics, widely used in structures and equipments of pearl farming, are a source of pollution to the detriment of the lagoon ecosystem. In order to evaluate the impact of MP on the physiology of Pinctada margaritifera, a species of ecological and commercial interests, adult oysters were exposed to polystyrene microbeads (micro-PS of 6 and 10 μm) for 2 months. Three concentrations were tested: 0.25, 2.5, 25 μg L-1 and a control. Ingestion and respiration rate and assimilation efficiency were monitored on a metabolic measurement system to determine the individual energy balance (Scope For Growth, SFG). Effects on reproduction were also assessed. The assimilation efficiency decreased significantly according to micro-PS concentration. The SFG was significantly impacted by a dose-dependent decrease from 0.25 μg L-1 (p < 0.0001). A negative SFG was measured in oysters exposed to 25 μg L-1. Gonads may have provided the missing energy to maintain animals’ metabolism through the production of metabolites derived from germ cells phagocytosis. This study shows that micro-PS significantly impact the assimilation efficiency and more broadly the energy balance of P. margaritifera, with negative repercussions on reproduction

Phenome of pearl quality traits in the mollusc transplant model Pinctada margaritifera

Abstract The bivalve Pinctada margaritifera exhibits three main transplant phenotypes derived from the donor (from which a mantle graft tissue, the saibo, is excised), the recipient (into which the saibo is implanted with a nucleus, leading to the formation of a pearl sac “chimera”) and the cultured pearls themselves. This first phenome study on the species derived from a large experimental graft. Transplant phenotype was assessed at three scales: 1) macro, pearl size, colour, grade, 2) micro, pearl surface microstructure, and 3) molecular, biomineralisation gene expression level in saibo and pearl sac tissues. From donor to pearl, the phenome revealed fine variations of quality traits dependent on the position on the mantle where the saibo was cut, whose variation could overlap with inter-individual donor phenotype differences. A single donor phenotype could therefore produce multiple pearl phenotypes at the scale of the saibo position, mirroring its original activity at the mantle position level and the colour and shape of the shell. This phenome study provides essential information on phenotypic trait architecture enabling us to explore and explain the main biological functions and pave the way for a phenomic project on P. margaritifera that could benefit the pearl industry

Feeding the pearl oyster Pinctada margaritifera during reproductive conditioning

This study aimed to model the food intake of P. margaritifera in order to examine the relationship between food level and reproductive activity. The effect of microalgae concentration on ingestion rate and assimilation efficiency was studied over a broad concentration range, using a mixture of Isochrysis galbana and Chaetoceros gracilis. Reproductive effort was assessed using three microalgae concentrations of 0.5, 7 and 18 cell μL-1. Reproductive status was assessed by gonad development index (GDI) – the ratio of the gonad surface to the visceral mass surface – and histological analysis of the gonad based on the presence (continuous or discontinuous) or the absence of gonial cells (GC). Ingestion is a saturating function of seston concentration for bivalves modeled with an adapted Michaelis- Menten function. The maximum ingestion rate of P. margaritifera adults was 193.50 106 cell.h-1.g-1 dw and the half saturation coefficient was 15 cell.μL-1. The concentration of 18 cell μL-1, supplied for 45 days induced a significantly higher GDI than the other treatments. GC decreased significantly and even stopped when pearl oysters were under-fed, suggesting that the mitotic process of the germinal stem cells was altered. Differentiation of germinal stem cells, therefore, appears to be controlled by food availability

Cryogrinding and sieving techniques as challenges towards producing controlled size range microplastics for relevant ecotoxicological tests

The impact of microplastics (MP) has attracted much attention from the scientific community and many laboratory assessments have been made of their effects on aquatic organisms. To produce MP from real environmental plastic waste, which would enable more realistic experiments, we used plastic pearl farming equipment from French Polynesian lagoons. Here, the pearl oyster Pinctada margaritifera could encounter MP coming from their breakdown in its surrounding environment. We tested an established method based on mechanical cryogenic grinding and liquid sieving. Our desired size range was 20–60 μm, corresponding to the optimal particle size ingested by P. margaritifera. The protocol was effective, generating MP particles of 20–60 μm (∼17,000–28,000 MP μg−1), but also produced too many smaller particles. The peak in the desired size range was thus flattened by the many small particles <3 μm (∼82,000–333,000 MP μg−1; 53–70% of total analysed particles), visible at the limit of Coulter counter analysis (cut-off point: 2 μm). Laser diffraction analysis (cut-off point: 0.4 μm) provided greater detail, showing that ∼80–90% of the total analysed particles were <1 μm. Diverging particle size distributions between those expected based on sieving range and those really observed, highlight the need to perform fine-scaled particle size distribution analyses to avoid underestimating the number of small micro- and nanoplastics (MNP) and to obtain an exact estimation of the fractions produced. Size and microstructure characterization by scanning electron microscopy suggested spontaneous particle self-assembly into crystal superstructures, which is the supposed cause of the divergence we observed. Overall, our results emphasize that particle self-assembly is a technical hurdle requiring further work and highlight the specific need to finely characterize the size distribution of MNP used in ecotoxicological experiments to avoid overestimating effects

Determination of gender in the pearl oyster pinctada margaritifera

The pearl industry in French Polynesia is based on exploitation of natural stocks of the black-lip pearl oyster (Pinctada margaritifera); it generates an annual turnover of 90 million euros. Improvements in pearl quality need genetic studies to improve the populations. This pearl oyster is a protandric species, where the sex-ratio normally is biased towards males. There is an increasing interest in gender control to find the mechanisms to augment female proportions for management purposes. This review summarizes information on exogenous and endogenous factors regulating gender in this and other bivalves and concludes that P. margaritifera is a protandric hermaphrodite, developing as a male during the first two years and without evidence of an effect from abiotic and biotic factors on gender during this phase. Later, pearl oysters progressively change to females, reaching a sex ratio close to 1:1 in specimens &gt;8 years; at this stage, gender is apparently influenced by environmental parameters, but particularly by stress. Future research should seek to accurately determine the effect of temperature and food on sex ratios. Studies should be performed to characterize genes responsible for expression of gender. The use of hormones is a path that might be explored to influence the gender of pearl oysters