Résumé : The New-Caledonian shrimp industry is based on the controlled reproduction of the shrimp Litopenaeus stylirostris, a species which was introduced in the 80s. The major difficulty to which the industry has been faced for 10 years is the occurrence of the “Syndrome 93”, which corresponds to mortality phases when the temperature falls down in April-May-June. This mortality is associated to the pathogenic bacteria Vibrio penaecida. An experiment of genetic selection based on the criterion ofsurvival to Syndrome 93 has been conducted at the Laboratory of Aquaculture of New Caledonia. The 3rd selected generation had demonstrated very encouraging results (survival rates improved by around 20% in experimental infections with V. penaeicida). These results have not been confirmed at the 4th generation and no difference in terms of physiology and immunology appears between the selected population and the non-selected control population. The potential causes of these results are examined and proposals for protocol improvements are given.
La filière crevette de Nouvelle-Calédonie reposesur la maîtrise de la reproduction contrôlée de la crevette Litopenaeus stylirostris, espèce introduite dans les années 1980. La difficulté majeure que rencontre la filière depuis une dizaine d’années est la récurrence du « Syndrome 93 », qui s’exprime sous forme d’épisodes de mortalités lors des baisses de température aux intersaisons. Ces mortalités sont associées à la bactérie pathogène Vibrio penaeicida Une expérience de sélection sur un critère de survie à des épisodes de Syndrome 93 a été menée au Laboratoire Aquacole de Calédonie. La 3èmegénération sélectionnée avait montré des résultats très encourageants (survies améliorées de l’ordre de 20% lors d’infections expérimentales à V. penaeicida). Ces résultats ne sont pas confirmés en 4ème génération et aucune différence en termes physio-et immunologique n’apparaît entre la population sélectionnée et la population témoin non sélectionnée. Les causes potentielles de ces résultats sont examinées et des propositions d’amélioration de protocoles sont avancées.

Droits : 2004 Université de la Rochelle, Ifremer
http://archimer.ifremer.fr/doc/00204/31527/29943.pdf
http://archimer.ifremer.fr/doc/00204/31527/

Éditeur(s) : Elsevier
Résumé : Two populations of the Latin American shrimp Penaeus (Litopenaeus)stylirostris domesticated in Hawaii and in New Caledonia were previously shown to be genetically differentiated and proven highly inbred. In New Caledonia, where different Vibriosis affect shrimp production and antibiotic use is banned in growing ponds, the Hawaiian population was introduced to increase the allelic variability available for local shrimp farmers and start a genetic improvement program. Growth and survival rates of the two pure populations and the two-way F-1-hybrids obtained by breeding Hawaiian animals with New Caledonian animals were assessed in several simple experiments (earthen ponds, floating cages and experimental infection challenges) during two years on two successive generations. Results were very consistent: F-1-hybrids growth rates in earthen ponds were 37% (+/-7% SD) higher than for pure populations. Cage experiments demonstrated no competition between the different populations when reared together or separately in a common environment. The F-1-hybrids also showed better survival rates in all experiments. Combining the results on growth and survival rates leads to the conclusion that biomass production is much higher with F-1-hybrid populations than with pure populations using the same quantity of juveniles stocked: biomass production in ponds was increased 1.4 and 2.3 times on year I and year 2 respectively, and 1.9 times in floating cages. The advantage of growing F-1-hybrids appeared proportionally higher when environmental and sanitary conditions led to poorer survival (34% in year 2 vs. 56% in year 1). These results are a good example of performance improvement by heterosis effect and/or of performance loss due to inbreeding in the pure populations. This study demonstrates that aquaculture industries which cannot afford large selection programs may benefit from using two different inbred parental stocks to produce F-1-hybrids for each commercial growout. This is notably true when only inbred populations are available, or when introduction of genetic variability from the wild or from other genetic resources represents a zoo-sanitary risk. In our case, the expected increase in L stylirostris production could be around 85% (according to our average results) if producers keep stocking their ponds at their current densities using F-1-hybrids. However, for sustainability reasons, it is advisable to stock F-1-hybrid animals at lower densities, the gain in performance allowing producing the same amount of biomass with less input. (C) 2008 Elsevier B.V. All rights reserved.
Aquaculture (0044-8486) (Elsevier), 2008-06 , Vol. 278 , N. 1-4 , P. 43-50

Droits : 2008 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/2008/publication-4316.pdf
DOI:10.1016/j.aquaculture.2008.03.018
http://archimer.ifremer.fr/doc/00000/4316/

Éditeur(s) : Elsevier
Résumé : In a previous study, we demonstrated the existence of an emerging cluster of Vibrio nigripulchritudo that proved to be associated with shrimp mortality events in New Caledonia. Using sequence polymorphisms evidenced in this previous MultiLocus Sequence Typing study, we developed two new quantitative PCR assays permitting the detection and quantification of V. nigripulchritudo at the genospecies level using SYBR Green I chemistry and at the emerging cluster level using Fluorescence Resonance Energy Transfer technology with hybridization probes. The use of this molecular diagnostic tool evidenced the colonization of the shrimp pond ecosystem by the pathogenic cluster at least at the onset of the disease. This new tool will allow better investigation of the dynamics of this bacterial pathogen in the shrimp farm ecosystem. (C) 2007 Elsevier B.V. All rights reserved.
Journal of Microbiological Methods (0167-7012) (Elsevier), 2007-07 , Vol. 70 , N. 1 , P. 30-38

Droits : 2007 Elsevier B.V. All rights reserved
http://archimer.ifremer.fr/doc/2007/publication-2729.pdf
DOI:10.1016/j.mimet.2007.03.007
http://archimer.ifremer.fr/doc/00000/2729/

Éditeur(s) : Elsevier
Résumé : Because Vibrio aestuarianus is known to cause serious infections in Pacific oyster Crassostrea gigas, a real-time PCR assay was developed targeting the dnaJ gene of this bacterium. Only V. aestuarianus strains isolated from C. gigas mortality events in different geographic areas and the reference strain tested positive, whereas no amplification products was obtained with type strains belonging to 23 other species of Vibrio. Sensitivity and reproducibility of the method were assessed using either seawater or oyster homogenate samples spiked with one V aestuarianus strain. All these samples were stored at -20 degrees C in order to mimic retrospective or grouped natural sample analysis without quantification bias due to prolonged freezing. Analysis of standard curves revealed excellent correlation values between light microscopy cell enumerations and PCR Threshold Cycle (Ct) values, and acceptable PCR reaction efficiencies for all type of samples. Quantification curves of both sample types were equivalent, with a detection level as low as 1.6 V. aestuarianus cells in the PCR reaction tube, corresponding to 1.6.10(2) cells ml(-1) and 1.6.10(2) cells mg(-1) in seawater and entire oyster samples, respectively, taking into account the dilution factor used for appropriate template DNA preparation. Comparison of PCR assay reproducibility according to the complexity of samples revealed that seawater samples gave more reproducible quantification measures than samples from oyster homogenate, with precision of measured Ct values inferior to 0.4 and 0.6 respectively at 99% confidence. Use of the real-time PCR assay allowed us to monitor V. aestuarianus load in oysters naturally infected with this pathogen. Furthermore, we were able to detect V aestuarianus in samples of seawater in which oysters had been reared and in algal cultures used for feeding oysters. Because of the rapidity and reliability of the real-time PCR assay method used in this study, just a few hours are needed compared with the two days required using the classic culture method, this technique will be particularly valuable in mollusc pathology laboratories, for monitoring the source and course of infections by V. aestuarianus in pathogenesis and epidemiologic studies, as well as for designing appropriate prophylactic control measures. (C) 2009 Elsevier B.V. All rights reserved.
Journal of Microbiological Methods (0167-7012) (Elsevier), 2009-05 , Vol. 77 , N. 2 , P. 191-197

Droits : 2009 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/2009/publication-6447.pdf
DOI:10.1016/j.mimet.2009.01.021
http://archimer.ifremer.fr/doc/00000/6447/

Éditeur(s) : Academic Press Inc Elsevier Science
Résumé : Several Vibrio species are known to be pathogenic to the Pacific oyster Crassostrea gigas. Survival varies according to pathogen exposure and high mortality events usually occur in summer during gametogenesis. In order to study the effects of gametogenetic status and ploidy (a factor known to affect reproduction allocation in oysters) on vibriosis survival, we conducted two successive experiments. Our results demonstrate that a common bath challenge with pathogenic Vibrio splendidus and Vibrio aestuarianus on a mixture of mature, spawning and non-mature oysters can lead to significant mortality. Previous bath challenges, which were done using only non-mature oysters, had not produced mortality. Immunohisto-chemical analyses showed the affinity of Vibrio for gonadic tissues, highlighting the importance of sexual maturity for vibriosis infection processes in oysters. Mortality rate results showed poor repeatability between tanks, however, in this bath challenge. We then tested a standardized and repeatable injection protocol using two different doses of the same combination of two Vibrio species on related diploid and triploid oysters at four different times over a year. Statistical analyses of mortality kinetics over a 6-day period after injection revealed that active gametogenesis periods correspond to higher susceptibility to vibriosis and that there is a significant interaction of this seasonal effect with ploidy. However, no significant advantage of triploidy was observed. Triploid oysters even showed lower survival than diploid counterparts in winter. Results are discussed in relation to differing energy allocation patterns between diploid and triploid Pacific oysters. (C) 2010 Elsevier Inc. All rights reserved.
Journal Of Invertebrate Pathology (0022-2011) (Academic Press Inc Elsevier Science), 2011-02 , Vol. 106 , N. 2 , P. 179-191

Droits : 2010 Elsevier Inc. All rights reserved.
http://archimer.ifremer.fr/doc/00030/14108/11368.pdf
DOI:10.1016/j.jip.2010.09.003
http://archimer.ifremer.fr/doc/00030/14108/

Résumé : Schemes optimisation for genetic improvement for growth of Penaeus stylirostris requires the development of technologies for grading shrimps easily. This work shows that bar and mesh graders are very suitable for early selection at post-larval stages, as long as early growth is heritable. Experimental data sets lead to the equations which give the grading weight as a function of the dimensions of the graders. Mesh graders which allow an earlier selection than bar graders (PL19 instead of PL25) open a new way to implement experimental selection into production hatcheries.
L’optimisation des schémas d’amélioration génétique de la croissance de Penaeus stylirostris, passe nécessairement par la mise au point des techniques de tri rapide et facile à mettre en oeuvre par les acteurs de la filière. Ce travail montre que les trieurs à barreaux ou à maille sont des outils adaptés à une sélection précoce en sortie d’écloserie, dans la mesure où la croissance précoce s’avèrerait héritable. Les tris expérimentaux ont permis d’établir les formules permettant de calculer les poids de tris en fonction des dimensions des trieurs. Les trieurs à maille qui permettent de trier les crevettes dès PL19 ouvrent des perspectives intéressantes pour intégrer une démarche de sélection expérimentale au sein des écloseries de production.

Droits : 2000 Ifremer
http://archimer.ifremer.fr/doc/00203/31439/29836.pdf
http://archimer.ifremer.fr/doc/00203/31439/

Résumé : Selective breeding of shrimp for viral resistance is established for species like L. vannamei and L. stylirostris. However, selection for bacterial infection resistance is not documented. In New Caledonia, "Syndrome 93" is a vibriosis that affects cultured shrimps during the cool season with survival from 15 to 30%. Current practises for breeders rearing at low densities do not improve the resistance of the offsprings mainly because selection pressures for "Syndrome 93" are low. Even after the fifth generation, survival improvement is not significant.
La sélection génétique de lignées de crevettes résistantes à certains virus a démontré son efficacité en particulier chez L. vannamei et L. stylirostris. En revanche, la sélection de crevettes résistantes à une bactérie du genre Vibrio est peu documentée. En Nouvelle-Calédonie, le « Syndrome 93 », vibriose à V. penaeicida, affecte toutes les fermes de crevettes L. stylirostris lors des élevages de saison fraîche. Les survies en bassins de grossissement, de l’ordre de 40 à 60% dans un élevage sain, tombent à des valeurs de 15 à 30%. L’élevage de géniteurs à faible densité, s’il maximise les performances de reproduction, ne semble pas optimiser la qualité de la descendance du fait des faibles pressions de sélection qui s’exercent vis-à-vis du syndrome 93. Les améliorations significatives du nombre d’animaux survivant aux infections et aux épisodes de mortalité en bassin restent faibles en valeur absolue à la 5ème génération de sélection expérimentale en conditions d’élevage, mais sur le long terme la stratégie testée pourrait se révéler économiquement efficace.

Droits : 2005 Ifremer
http://archimer.ifremer.fr/doc/00117/22848/20658.pdf
http://archimer.ifremer.fr/doc/00117/22848/

Éditeur(s) : Academic Press Ltd- Elsevier Science Ltd
Résumé : The understanding of reciprocal interactions between Crassostrea gigas and Vibrio sp., whether these be virulent or avirulent, is vital for the development of methods to improve the health status of cultured oysters. We describe an original non-invasive experimental infection technique using cohabitation, designed to explore these interactions. Using real-time PCR techniques we examined the dynamics of virulent and avirulent Vibrio sp. in oyster hemolymph and tank seawater, and made a parallel study of the expression of four genes involved in oyster immune defense: Cg-BPI, Cg-EcSOD, Cg-IκB, Cg-TIMP. No mortality occurred in control animals, but oysters put in cohabitation for 2–48 h with animals previously infected by two Vibrio pathogens suffered mortalities from 2 to 16 days post-cohabitation. Our results show that virulent Vibrio infect healthy individuals after only 2 h of cohabitation, with values ranging from 4.5×102 to 2×104 cells ml−1 hemolymph. Simultaneously, an approximate ten-fold increase of the total Vibrio population was observed in control animals, with a 6.6–78.5-fold up-expression of targeted genes. In contrast, oysters exposed to harmful bacteria had mean expression levels strongly down-regulated by a factor of 9.2–29 (depending on the gene) compared with control animals. Although oysters were still found to be infected by virulent Vibrio after 6–48 h of cohabitation, no significant differences were noted when comparing levels of each transcript in control and infected oysters at the same sampling times during this period: the important differences were noted before 6 h cohabitation. Taken together, our data support (1) the hypothesis that virulent Vibrio disturbs the immune response of this invertebrate host both rapidly and significantly, although this occurs specifically during an early and transient period during the first 6 h of cohabitation challenge, and that (2) expression of targeted genes is not correlated with vibriosis resistance.
Fish & Shellfish Immunology (1050-4648) (Academic Press Ltd- Elsevier Science Ltd), 2011-02 , Vol. 30 , N. 2 , P. 691-699

Droits : 2011 Elsevier Ltd All rights reserved.
http://archimer.ifremer.fr/doc/00025/13604/10681.pdf
DOI:10.1016/j.fsi.2010.12.017
http://archimer.ifremer.fr/doc/00025/13604/

Éditeur(s) : Elsevier
Résumé : A collection of 57 isolates of Vibrio nigripulchritudo from either diseased or healthy shrimp and from shrimp farms environment was studied in order to gain a better understanding of the epidemiology of this pathogen, notably isolated from two distinct shrimp disease complexes. Molecular typing using two different techniques, arbitrarily primed PCR (AP-PCR) and multi-locus sequence typing (MLST), studied together with experimental pathology data allowed a relevant epidemiological insight into this possibly emerging pathogen. Additionally, results obtained with the two molecular typing techniques were congruent and allowed discriminating the strains associated with the "Summer Syndrome" from strains isolated from other contexts, especially the other shrimp vibriosis "Syndrome 93". These results highlight that the "Summer Syndrome" is most probably caused by an emergent clonal pathogen that therefore deserves surveillance and that AP-PCR can satisfactorily be used for that purpose
Systematic and Applied Microbiology (0723-2020) (Elsevier), 2006-11 , Vol. 29 , N. 7 , P. 570-580

Droits : 2005 Elsevier
http://archimer.ifremer.fr/doc/2006/publication-1913.pdf
DOI:10.1016/j.syapm.2005.12.005
http://archimer.ifremer.fr/doc/00000/1913/

Résumé : L’élevage des crevettes pénéides a connu un développement spectaculaire à l’échelle mondiale depuis les années soixante-dix, en particulier grâce à la maîtrise de l’ensemble du cycle biologique en captivité de plusieurs espèces d’intérêt aquacole (Aquacop, 1979). Elle a en effet permis de s’affranchir de l’approvisionnement aléatoire en juvéniles de pêche et en géniteurs sauvages, et par voie de conséquence de domestiquer ces espèces, c'est-à-dire de les sélectionner spontanément pour de meilleures aptitudes à l’élevage. Cette évolution est similaire à celle de filières piscicoles. Cependant les pathologies infectieuses représentent un frein important au développement ultérieur de ces activités. De manière générale, une pathologie infectieuse est la conséquence d’une rupture d’équilibre entre un hôte, son environnement et un ou plusieurs pathogènes (Lightner & Redman, 1998). Toute tentative de lutte contre une pathologie nécessite une meilleure connaissance de ces 3 compartiments ainsi que leurs interactions. Le présent rapport vise à synthétiser les informations scientifiques essentielles utiles à la mise au point de stratégies de lutte contre ces pathologies en pénéiculture. Un premier point sur les pathogènes sera développé avant d’évoquer les principaux descripteurs de la santé de la crevette. Enfin, les différentes possibilités de gestion des pathologies en crevetticulture, dont l’une est la sélection génétique, seront passées en revue.

Droits : 2004 Université de la Rochelle, Ifremer
http://archimer.ifremer.fr/doc/00204/31528/29944.pdf
http://archimer.ifremer.fr/doc/00204/31528/

Éditeur(s) : Elsevier
Résumé : The Summer Syndrome is a new shrimp disease that has been affecting a shrimp growout farm in New Caledonia since end of 1997. It was recognized to be caused by a systemic vibriosis due to Vibrio nigripulchritudo. This new disease turned out almost immediately enzootic in the shrimp farm involved and has affected all its crops ever since. Since the year 2000, V. nigripulchritudo strains have been found in several shrimp farms, although Summer Syndrome is still limited to one particular area, affecting, since 2003, two adjoining farms. As part of a multidisciplinary research program, a high-frequency survey was carried out during the summer 2002-2003 in two shrimp farms: one affected farm and another one in which pathogenic strains could be isolated but without any disease event. It permitted a good description of V. nigripulchritudo dynamics in shrimp and the ecosystem in both farms. The study of virulence characteristics of some isolates showed that pathogenic and non-pathogenic strains occur in the shrimp farms environment and that both may be found at the same time in one farm. Our results strongly suggest a persistence of pathogenic strains in wet zones of the pond sediment at low concentrations between crops in the affected farm, and their development during the rearing cycle as a cause of shrimp infection.
Aquaculture (0044-8486) (Elsevier), 2006-03 , Vol. 253 , N. 1-4 , P. 105-113

Droits : 2005 Elsevier B.V. All rights reserved
http://archimer.ifremer.fr/doc/2006/publication-1110.pdf
DOI:10.1016/j.aquaculture.2005.07.031
http://archimer.ifremer.fr/doc/00000/1110/