PROCESS FOR OBTAINING OYSTERS RESISTANT TO PATHOGENS

Abstract

The present invention relates to a method for obtaining oysters resistant to pathogenic agents and to the oysters thus obtained. The method of the invention consists of the hybridization of a Mediterranean Ostrea edulis oyster resistant to said pathogenic agents and a non-resistant oyster of the opposite sex. The present invention finds particular application in the commercial production of farmed oysters resistant to pathogenic agents such as Bonamia Ostreae and Martelia Refringens.

Description

Technical field The present invention relates to a method for obtaining oysters resistant to pathogenic agents and to the oysters thus obtained. The present invention finds particular application in the commercial production of farmed oysters resistant to pathogenic agents such as Bonamia Ostreae and Martelia Refringens. In the description below, references in brackets ([]) refer to the list of references presented after the examples. State of the art The flat oyster Ostrea edulis is one of the most cultivated oyster species in Europe, but also in the United States and Canada. In the 1970s and 1980s, the appearance of the parasites Martelia refringens and Bonamia ostreae caused a sharp decline in oyster production, forcing oyster farmers to seek ways to combat these parasites. Several measures were taken to limit oyster infection. One measure was to limit the movement of oysters from one hatchery to another and to limit the movement of spat from one region to another. Another measure was to try to select oysters resistant to the parasite Bonamia Ostreae, Naciri-Graven et al. (1998) "Selecting the fiat oyster Ostrea edulis (L.) for survival when infected with the parasite Bonamia ostreae." J.Exp. Mar Biol. Ecol., 224:91-107 [1]. These selections made it possible to highlight oysters tolerant to said parasites but not resistant and caused a weakening of the genetic diversity of cultivated oysters as well as a harmful increase in inbreeding of oysters, N. Taris et al. "Genetic consequences of the production of oyster larvae in hatcheries: study of the processes of drift and selection.", The proceedings of the BRG, 6 (2006) 521-541. [2], Other studies have been conducted to identify uninfected oyster culture areas using susceptible spat from the Atlantic. One such study was conducted in Corsica in the 1980s in the Diana pond, resulting in the classification of this pond as an infected area on the proposal of IFREMER, under European Council Directive 91 / 67 / EEC on the animal health conditions governing the placing on the market of aquaculture animals and products. Zone I, which encompasses all of Corsica, is classified as not free from bonamiosis and marteliosis. These various studies have made it possible to establish a map of areas infected by parasites and even to select oysters by area that are more tolerant to parasites but weaken their genetic diversity. None of these studies have resulted in the production of oysters resistant to these parasites. There is therefore a real need for a process for obtaining pathogen-resistant oysters that overcomes the defects, drawbacks and obstacles of the prior art and allows industrial production to be controlled at reduced costs. This process must be simple to implement. Description of the invention The present invention aims precisely to meet the aforementioned needs and drawbacks by providing a method for obtaining oysters resistant to pathogenic agents. The method of the invention is characterized in that it comprises the hybridization of a Mediterranean oyster Ostrea edulis resistant to said pathogenic agents and a non-resistant oyster. The invention also relates to pathogen-resistant oysters obtainable by the method of the invention. According to the invention, resistant oysters are understood to mean any Mediterranean Ostrea edulis oyster that is resistant to pathogens. The resistant Mediterranean Ostrea edulis oyster can be any resistant wild oyster originating from the Mediterranean. For example, all Mediterranean Ostrea edulis oysters that have not been subjected to anthropogenic selective pressure or genetic contamination, for example by breeding and / or by the transplantation of cultured strains from the Atlantic. The Mediterranean origin of oysters can be verified by molecular analyses of the strains by allozyme markers, microsatellite markers, Launey S. et al. “Geographic structure in the European fiat oyster (Ostrea edulis L.) as revealed by Microsatellite polymorphism.” J Hered. 2002 Sep-Oct;93(5):331-51. (2002) [3], or RNA sequences. For example, a molecular marker that can be used to highlight the Mediterranean origin of the layer corresponds to the 313 base pair sequence of the mitochondrial 12s-rRNA gene of the strains as presented in the scientific article Diaz-Almela et al. “Reduced female gene flow in the European fiat oyster Ostrea edulis”.J Hered. 2004 Nov-Dec;95(6):510-6. (2004) [4], . The resistant oyster may be chosen so as to preferably have technical growth qualities and condition indices, i.e. a proportion of edible flesh relative to the total weight, which are most suitable for the hybridization process. For example, said proportion may be between 0.10 and 0.20, preferably greater than 0.15. The measurement may be carried out, for example, on the largest oysters within an age class and having a suitable shell conformation, i.e. a lower valve convexity. The resistant oyster may be chosen, for example, from young oysters of first maturity, for example weighing less than 80g for the Corsican oyster, larger oysters tending to produce a higher proportion of shell.Among these, we can preferably retain individuals presenting a convexity, defined as being the ratio of the thickness to the average diameter [(length + width) / 2], greater than 0.33. Resistant oysters can be selected based on their phenotypic characteristics such as size, weight etc. For example, the resistant Ostrea edulis oyster from the Mediterranean can be chosen, preferably, with a diameter greater than 60mm. Resistant oysters can also be chosen based on their location in the natural growth environment. For example, between free-living forms, scattered on the surface of the sediment, and oysters attached to rocky parts in their natural environment, free-living forms are preferred because they have characteristics more suited to farming. Oyster collection areas at natural sites are preferably those with the largest population, i.e. with the highest productivity. For free-living forms occupying soft sediment, oysters may be selected, for example, from populations with a density greater than 1 individual per m2, and preferably greater than 2 individuals per m2. The resistant Ostrea edulis oyster can be chosen, for example, from the resistant Ostrea edulis oysters of the Mediterranean, oysters from the lagoons of Corsica, from Morocco to Nador, from Tunisia to Gabes, from Libya, from Greece, from Murcia in the Mar Menor in Spain, from the Aegean region and the Bosphorus in Turkey, from Menorca to the Balearic Islands, from Ukraine to Sevastopol, from the Red Sea and / or from the Baltic Sea. Preferably, for carrying out the method of the invention, the resistant Ostrea edulis oyster is chosen from the group comprising the wild Corsican oyster Ostrea edulis from the Diane ponds, the Urbino ponds, the Gulf of Porto Vecchio, the Gulf of Santa Manza and the lagoons of Sardinia. Preferably, for carrying out the method of the invention, the resistant Ostrea edulis oyster chosen is the wild Corsican oyster Ostrea edulis from the Diane ponds. 2 5 According to the invention, resistant Mediterranean oysters can be oysters from ancient Mediterranean beds. The oysters are preferably wild flat oysters that have not undergone external genetic input from transplantation or farming and / or oysters from geographically limited Mediterranean lagoons. Wild populations 30 established for a long time in Mediterranean lagoons have the genotypic, phenotypic and zootechnical characteristics specific to the contribution of the particular adaptive qualities attached to their biotope, in particular the levels and amplitudes of temperatures, the levels and variations of salinity, the oxygenation of the environment, the trophic qualities of the environment, and the tides and the resistance to possible deflooding of natural deposits. For example, the natural oyster beds of the Nador lagoon in Morocco can be deflooded for several hours at spring tides and subjected to the subtropical sunshine of the region without suffering mortality. The resistant oyster can be a Nador oyster for carrying out the process of the invention, for example to obtain a hybrid suitable for farming on foreshore in the Atlantic. However, resistant Mediterranean strains from open and nutritionally depleted biotopes inherit common adaptive traits that are generally not conducive to hybridization quality. This is the case for resistant strains from the Greek Cyclades islands, Croatia, Calabria, Sicily, and Camargue (Port-Saint-Louis-du-Rhône). The Mediterranean origin of oysters can be verified for example by molecular analyses of strains using allozyme markers, microsatellite markers [3] or RNA sequences [4] as described previously. According to the invention, advantageously the chosen resistant oyster has a level of carbohydrate reserves appropriate for hybridization. These reserves, consisting of glycogen, will gradually give the appearance of a "fat" oyster capable of developing its gonad and producing its gametes. These reserves can be mobilized in the spring for the production of gametes and throughout gametogenesis; thus, the nutrition of the parents conditions fertility and recruitment. The carbohydrate reserves make it possible to promote the expression of full fertility in the oysters and therefore the implementation of the method of the invention. According to the invention, the resistant Mediterranean oyster Ostrea edulis is preferably chosen at a reproductive age, preferably at the age of first reproduction. Choosing the oyster at the age of first reproduction in fact makes it possible to guarantee a maximum survival rate of the gametes for the completion of hybridization. According to the invention, by non-resistant oyster is meant any sensitive oyster, vulnerable to pathogenic agents, whatever its origin or species. The non-resistance of the oyster to pathogenic agents can manifest itself by any alteration of the biological functions of the oyster which can lead for example to a modified, reduced, or stopped growth of the oyster. The non-resistance to pathogenic agents can also lead to the death of the oyster. In the case of bonamiosis, the first indication of infection often occurs following slowed growth, lesions on the gills, opening of the valves, accompanied by high mortality generally appearing from the first sexual maturation.For marteliosis, known as "Abers Disease", the following clinical signs appear in farms in abers or on the foreshore: emaciation and depletion of glycogen reserves, complete discoloration of the digestive gland, cessation of feeding and weakening of the oyster, signs followed by high mortality. According to the invention, the non-resistant oysters that can be hybridized according to the method of the present invention can be chosen from wild oysters, hatchery oysters, native oyster strains, native Mediterranean oysters and oysters of origin outside the Mediterranean. For example, the non-resistant oyster can be an oyster from the Atlantic, the Pacific and / or the Indian Ocean. According to the invention, the non-resistant oyster may be, for example, a Mediterranean oyster degenerated by oyster farming practices or polluted by the transfer of sensitive and / or contaminated oysters from the Atlantic, the Pacific and / or the Indian Ocean. According to the invention, a non-resistant oyster may be of a genus or species identical to or different from those of the resistant Ostrea edulis oyster. For example, non-resistant oyster species which may be used in the invention may belong to the genera and / or species, but not limited to, Ostrea edulis, Ostrea angasi, Ostrea conchaphila, Ostrea. lurida, Ostrea denselamellosa, Ostrea puelchana, Ostrea folium, Ostrea permollis, Ostrea stentina, Tiostrea chilensis, Crassostera virginica, Crassostrea gasar and Crassostrea Rhizophorae, etc. The non-resistant oyster can be chosen, for example, from the group including Crassostrea gasar mangrove oyster, from the estuaries and mangroves of West Africa, Crassostrea Rhizophorae mangrove oyster, Indo-Pacific etc. The non-resistant Ostrea edulis oyster can be chosen, for example, from the group including flat oysters from the Thau lagoon "Bouzigues", oysters from the Venice lagoon: flat Venice oyster, flat "Gravettes" oysters from the Arcachon Basin, Charente and / or Vendée, the flat oyster from South Brittany "Belon" from Abers and the Gulf of Morbihan, "Cancales" from northern Brittany and Normandy, oysters from Galicia in Spain, oysters from Portugal, oysters from Great Britain in Cornwall, oysters from the south and north of Ireland, oysters from the Netherlands, oysters from Denmark, oysters from the USA and Canada from the West Atlantic, from Florida to Quebec, oysters from the East Pacific from the coasts of USA and Canada, oysters from coasts ranging from California to Alaska. The non-resistant oyster may be infected or uninfected, tolerant or non-tolerant to pathogenic agents for the implementation of the method of the invention. Said oyster is said to be tolerant when it is capable of reproducing a first time before having expressed the pathologies that it carries. According to the invention, for the implementation of the method of the invention, the resistant Mediterranean oyster Ostrea edulis and the non-resistant oyster are preferably chosen at the end of the sexual rest period. This period is normally in winter. Said resistant and non-resistant oysters are then preferably conditioned for hybridization, for example in hatchery tanks, for example in increasing photoperiod. According to the invention, the oysters can be individually marked according to their resistance or non-resistance to pathogenic agents. The marking can be carried out by any of the means known to those skilled in the art, for example by scarification or by gluing a label with glue, for example by epoxy glue. This individual marking of the oysters makes it easier to create homogeneous batches of hybrid spat. According to the invention, the oysters used for hybridization are of opposite sex. The flat oyster of the genus Ostrea is an asynchronous bivalve with sexuality consecutive rhythmic. Generally protandrous, it can change sex several times in the same season, which makes sexing difficult because the male and female lines coexist simultaneously. This specific mode of reproduction attached to the genus Ostrea prohibits any control of genetic identities in the case of mass reproduction. It is therefore preferable to isolate the oysters two by two, in the case where hybridization involves resistant and non-resistant oysters of the genus Ostrea. In theory, each pair of isolated oysters should only have a one in two chance of forming the male-female couple. Advantageously in the present invention, fertilization occurs at the level of 70 to 80% of the couples. Indeed, the maturation of the earliest oyster can cause an inverse orientation of the sex of the second oyster. The number of hybridizations obtained by the present invention is therefore higher than the theoretical number assumed. It is noteworthy that oysters are largely eurythermic and euryhaline. These tolerances facilitate the synchronization of maturation and remission of gametes, and the hybridization of two oysters from singular geographical environments. According to the invention, the pathogens can be chosen from the group comprising bacteria, parasites and viruses. According to the invention, the pathogenic agents may be chosen from the group comprising haplosporidia, protozoa, martelias, parasites and external contaminating agents using the general cellular and / or humoral immunity mechanisms of oysters, for example the pathogenic agents Bonamia ostreae and Martelia refringens. According to the invention, said pathogenic agents may be responsible for pathologies, for example, bonamiosis, marteliosis, haplosporidosis, microcytosis, perkinsosis and / or irivovirosis, preferably the pathogenic agents are responsible for bonamiosis and / or marteliosis. Means for implementing the method of the present invention are described below. According to the invention, the hybridization can be carried out in any tank known to those skilled in the art allowing the hybridization of the oysters. For example, the tank may be a hatching tank, an aquarium, any tank, basin, basin made of glass, wood, metal, synthetic material or masonry, or any suitable container. The volume of the tank used to carry out the method of the invention may be, for example, a volume of 1 to 100 liters, preferably 5 to 20 liters. According to the invention, the tank may comprise means for oxygenating the water. For example, the water may be oxygenated using any means known to those skilled in the art, for example by a pump allowing the expulsion of air into the water of the tank. Oxygenation may also be carried out at the water circuit. The water oxygenation flow rate may be adapted during the hybridization, preferably so as to saturate the aquatic environment with dissolved oxygen, whatever the temperature and salinity levels required according to the invention. The oxygen level may be from 5 mg / l to 11 mg / l, preferably greater than 6.5 mg / l. According to the invention, the tank comprising the oysters to be hybridized may be, for example, previously filled with water, supplied continuously or discontinuously by a water circuit. The water circulation flow rate can be between 0 l / h and 100 l / h, preferably between 5 l / h and 20 l / h.The flow rate can be adjusted to the respiration and feeding needs of the oysters and larvae. According to the invention, said water circuit can be isolated from one tank to another. Isolating the water circuit makes it possible, in particular, to avoid external influences on the oysters to be hybridized, and thus to guarantee the purity of the hybrid larvae. This isolation makes it possible, for example, to prevent the production of hybrids with undesirable genetic contamination. According to the invention, the water used in the present invention may be any water suitable for carrying out the hybridization. The water suitable for carrying out the invention may be, for example, water having physicochemical characteristics, for example salinity, pH, temperature, etc., identical, intermediate or different from those of the original environment of the non-resistant oysters and / or those of the environment of the resistant oysters. According to the invention, the water may have a different composition depending on the steps of the method of the invention. According to the invention, the water used may have a salinity of between 3% and 50%, preferably between 12% and 38%. It may have a pH of between 6.5 and 9, preferably between 7 and 8.5. It may be at a temperature of between -8°C and +55°C, preferably between 12°C and 40°C. According to the invention, the nutritional supply for carrying out the invention may consist of any nutritional source known to those skilled in the art for oyster culture and / or for oyster hybridization. Said nutritional supply may consist, for example, of unicellular algae, phytoplankton, benthic bacteria, supply of food microparticles, compound feed, supply of dissolved organic matter such as sugars, proteins, vitamins, etc., or a mixture thereof. Phytoplankton, benthic bacteria, and unicellular algae can be sourced from hatcheries and / or natural oyster growing environments. Microparticles can be of natural or artificial origin, for example, from organic waste and / or aquaculture discharges. Unicellular algae and / or phytoplankton can be, for example, concentrated by centrifugation in the form of refrigerated paste, food microparticles can be, for example, in suspension and / or in emulsions, compound foods can be, for example, dry or hydrated, combining carbohydrate and / or lipid and / or protein materials, possibly extruded, calibrated or in microcapsules. The unicellular algae cultivated in hatcheries and / or in the natural environment may be chosen from the group comprising Isochrysis galbana, Skeletonema costatum, Pavlova lutheri, Chaetoceros calcitrans, Tetrase / mis sp. etc. For example, the phytoplankton may be chosen from the group comprising: Isochrysis galbana, Pavlova lutheri, Chaetoceros forma pumilum etc. The quantity and quality of the phytoplankton and unicellular algae used are preferably adapted to carrying out the method of the invention. Nutrition is an important element for the fertility of the broodstock and the success of recruitment into hybrid larvae and oysters. In this document, the term "hybridization" means all methods known to those skilled in the art for carrying out hybridization between at least one resistant oyster and one non-resistant oyster as described above. Hybridization can also be carried out directly with the gametes of the resistant and / or non-resistant oysters described above by sperm cryopreservation techniques according to the work of Lannan JE, 1971, Experimental self-fertilization of the Pacific oyster, Crassostrea gigas, utilising cryopresen / ed sperm, Genetics, 68: 599-601 [5], Bougrier and Rabedomanana, 1986. Cryopreservation of spermatozoa of the Japanese oyster, Crassostreea gigas. Aquaculture, 58: 277-280 [6], or by means of the multispecific gamete preservation and washing diluents Haffray et al. “Domestication and genetic improvement of fish stocks within the framework of SYSAAF”, INRA Prod. Anim., 2004, 17 (3), 243-252 [7], Zootechnical knowledge can help control the artificial reproduction of identified individuals, by controlling sex, by the individual maturation of the parents, by the synchronization of spawning and by chemical exchanges between parents. This knowledge has been the subject of a scientific synthesis publication: Gérard A., Naciri-Graven Y., Boudry P., Launey S., Heutebise S., Ledu C., Phelipot P., (1997). Control of gametogenesis of cupped and flat oysters. In: The natural and controlled reproduction of Bivalves cultivated in France, Devauchelle N., Barret J., Salaun G., (1997), DRV / RA / RST 97-11, Ifremer Brest, 217 pp. [8], . According to a particular embodiment of the invention, the hybridization can comprise the following steps: (a) provide a Mediterranean oyster Ostrea edulis resistant to said pathogens, (b) providing an oyster not resistant to said pathogens of the opposite sex to said resistant Ostrea edulis oyster, (c) placing said oysters together in a tank containing water having a salinity permitting hybridization, d) maturation of said oysters in said tank, preferably in increasing photoperiod, with sufficient nutritional intake for said maturation, (e) induction of the emission of male gametes by means of an induction agent applied to oysters, (f) fertilization of the female gametes by the male gametes emitted in step (e), g) incubation of the larvae obtained in step f) for 8 to 10 days, h) feeding the larvae from step g) with phytoplankton so as to obtain eyed larvae, (i) harvesting the eyed larvae obtained, and j) fixing said larvae on a development support in order to obtain at least one oyster resistant to said pathogenic agents. According to the method of the invention, the pathogen-resistant Mediterranean Ostrea edulis oyster provided in step a) is a resistant oyster as described above. According to the method of the invention, the non-pathogen-resistant oyster provided in step b) is a non-resistant oyster as described previously. According to the method of the invention, step c) consists of putting together at least one oyster provided in step a) and at least one oyster provided in step b) in a tank. For example, several oysters provided in step a) can be put with one oyster from step b) in a tank and vice versa. Several oysters provided in step a) can also be put with several oysters provided in step b) in a tank. Preferably, said oysters provided in steps a) and b) in the process of the invention are isolated two by two in step c) of the process of the invention, that is to say that each tank contains only two oysters, one corresponding to an oyster provided in step a) and the other corresponding to an oyster provided in step b). The tank used in the method of the invention may be a tank as described above. Steps d) to i) can be carried out with the implementation means described previously. These means can be adapted to each step of the method of the invention. According to the method of the invention, the maturation carried out in step d) of the method of the invention can be carried out by any means known to those skilled in the art allowing the maturation of the oysters. Preferably, the maturation of the oysters is carried out by progressively increasing the photoperiod. This increase can be carried out over a period of one week to 6 months, preferably from 1 month to 3 months. The minimum lighting time is between 1 h and 12 h, the maximum lighting time can be between 12 h and 23 h. The maturation step can be carried out at any temperature allowing the implementation of the method of the invention. Preferably, said maturation can be carried out with a progressive increase in temperature up to a temperature preferably between 20 and 30°C. Preferably, the maturation is carried out at a temperature between 20 and 30°C.The choice of the final maturation temperature depends in particular on the strains used during the hybridization process and their responses to maturation. The temperature can be adapted according to the oysters to be hybridized. The control of the response of the oysters at this stage can be carried out by controlling the maturity of the gonads and the formation of the gametes. The oysters have different stages of maturity numbered from 0, corresponding to sexual rest, to 4b corresponding to the emission of gametes. The control of maturity can be carried out by methods known to those skilled in the art, for example by observing the opening of the valves under anesthetic bathing using magnesium chloride (MgCl2). In the method of the invention, the oyster is considered mature when it has reached stage 3 of maturation of the gonads. During this maturation stage, the nutritional intake may be carried out by any appropriate means known to those skilled in the art. This may be, for example, a nutritional intake as defined above. This may be, for example, example of unicellular algae, phytoplankton, benthic bacteria, food microparticles etc. In a particular embodiment in which the tank is supplied by a water circuit, during the maturation step, said circuit can be isolated from one tank to another. The isolation of the water circuit makes it possible, among other things, to avoid exchanges of water from tank to tank and therefore exchanges of substances, for example proteins and / or pathogens and / or chemical substances that may be emitted by mature oysters cultivated in other tanks. These substances may in fact be capable of directing the sex of the parents. The exchanges of gametes emitted by mature oysters cultivated in other tanks, undesirable for carrying out the invention, may cause untimely self-fertilization between sister lines. According to the invention, the induction of gamete emission as defined in step e) of the method of the invention is preferably carried out on mature oysters, for example oysters at stage 3 of gonad maturation. These mature oysters may be, for example, the oysters obtained in step d) of the method of the invention. The induction agent used in step e) of the method of the invention may be any induction means known to those skilled in the art, for example at least one thermal shock and / or at least one protein, for example a hormone, a chemical substance or a neurotransmitter, for example serotonin. Preferably, the induction agent may be one or more thermal shocks. It corresponds to a successive decrease and increase in temperature, the temperature variation being adapted to the implementation of the method of the invention. For example, the maximum temperatures may be between 25°C and 55°C and the minimum temperatures between 5°C and 20°C. Induction, for example, heat shock, allows the release of male gametes first, which stimulates the spawning of female gametes. The induction of female gamete release is carried out chemically by male gametes. This can be, for example, a hormone or a neurotransmitter, such as serotonin. The induction of the emission of female gametes can also be carried out by any substance known to those skilled in the art inducing the emission female gametes. For example, a chemical, hormone or neurotransmitter, e.g., serotonin, preferably water containing male gametes, filtered water that has contained gametes and / or a dilution medium containing cryopreserved active sperm. In a particular embodiment, step e) of inducing remission of gametes by the oysters is preferably carried out in a tank without water circulation in order to avoid the dispersion of the gametes. In this case, if water circulation takes place in the previous steps, for this step e), the water circuit is cut off. In another particular embodiment of step e), the circulation of water from one tank to another can also be isolated in order to avoid the dispersion of substances such as hormones or male gametes in the other tanks. According to the method of the invention, step f) corresponds to the fertilization of the female gametes by the male gametes, the male gametes being previously filtered by the female oyster. Fertilization takes place in the mantle cavity of the oyster. The means for implementing this step may be those as described previously or any means known to those skilled in the art. These means are, of course, preferably suitable for carrying out fertilization. According to the method of the invention, the incubation of the larvae as defined in step g) can be carried out, preferably in the mantle cavity of the oyster. During this larval incubation step, the means for implementing this step can be those as described previously or any means known to those skilled in the art. These means are preferably suitable for carrying out this incubation. This incubation step can be carried out for 8 to 10 days. During this incubation step, the oysters and larvae can be fed, for example, with phytoplankton as described previously or any other suitable nutrient. After this incubation period, the larvae are released into the environment. According to the method of the invention, steps e) and g) corresponding to the induction of spawning, fertilization and incubation of the larvae can be carried out in vitro, outside the mantle cavity or in vivo inside the mantle cavity of the female. When step g) is carried out in vivo, i.e. in the mantle cavity of the female oyster, the gametes are filtered, fertilized and incubated in the mantle cavity of the female oyster. The incubation is carried out in such a way that it allows the expulsion of larvae in step g). In vitro, gametes are obtained by scarification of the gonads (stripping technique), allowing the stages of development and fertilization to be programmed and controlled. According to the method of the invention, step h) corresponds to the feeding of the larvae released into the medium in step g) in order to obtain eyed larvae. The phytoplankton allowing the feeding of the larvae as described above may be any phytoplankton known to those skilled in the art allowing this step to be carried out. The means for implementing this step may be those as described above or any means known to those skilled in the art / These means are preferably suitable for carrying out the feeding of the larvae. According to the method of the invention, step i) corresponds to the harvesting of the eyed larvae obtained in step h). The harvesting of the eyed larvae can be carried out, for example, 8 to 10 days after expulsion of the larvae. The means for harvesting the eyed larvae can be any means known to those skilled in the art, for example filters, sieves having pores with a diameter allowing the harvesting of the larvae. For example, the sieves can have a pore size ranging from 10 μm to 180 μm, preferably from 50 μm to 150 μm. The pore size can be chosen according to the size of the emitted larvae, this having to be smaller than the size of the emitted larvae. According to the method of the invention, step j) corresponds to the attachment of the larvae to development supports. The attachment can be carried out in tanks as described previously. The means for implementing this step can be those as described previously or any known means of the person skilled in the art. These means are preferably adapted to carry out fertilization. Said tanks may comprise identical or different development supports at their wall. The larval development supports may be any support allowing the method of the invention to be carried out. For example, the development support may be micro-broken oyster shells, mussel shells, micro-broken glass, and / or any material, sieved for example between 250 μm and 500 μm, allowing the attachment of the larvae obtained by the method of the invention and the obtaining of free spat. After the fixation stage, the spat develop in order to obtain at least one hybrid oyster. The means for implementing this development stage may be those described above or any means known to those skilled in the art. These means are preferably adapted to the development of the larvae. According to the invention, hybridization can be carried out, for example, over a single breeding season, for example over a period of six months during the year of first maturity. The temperature and feeding conditions can be chosen to allow each oyster to reverse its sex several times during its first maturity. Said oysters are capable of emitting new gametes at intervals varying from 10 to 70 days. Advantageously, carrying out the process of the invention in the first year of maturity can provide optimal quality of gametes and larvae from young oysters. The hybrid oysters obtained according to the method of the invention are full-sib types, they come only from parents presenting particular genetic polymorphisms resulting from their distinct and complementary ecological and geographical identities added by heterozygosity. This hybridization and this formation of heterozygotes make it possible to obtain hybrids presenting characteristics of resistance to pathogenic agents. Hybridization according to the method of the invention never occurs in nature, in particular due to the reproductive biology of the genus Ostrea and the geographical distance of genetically diverse wild populations. distinct. The breeding system preferably uses only F1 hybrids, the qualities of heterosis being lost very quickly in subsequent generations through inbreeding degeneration to which Ostreidae are particularly vulnerable. The process of the invention therefore makes it possible to obtain resistant first-generation oysters. Resistant hybrid oysters can develop in different conditions. Depending on the hybridization carried out, they can develop in the original environments of the parents. For example, crossing a resistant Ostrea edulis oyster from Corsica with a non-resistant oyster from the Atlantic produces a hybrid resistant to pathogens capable of developing on the Atlantic coasts and also in the Mediterranean. This aspect of the invention has a great advantage over the state of the art, knowing that the resistant oyster from Corsica cannot develop on the Atlantic coasts, Corsican oysters not being adapted, for example, to the tidal phenomenon and therefore to the phenomenon of immersion and emersion, to variations in the environment, for example salinity, temperature. These resistant oysters obtained by hybridization, thanks to their resistance and their ability to adapt to the environment, make it possible to reduce costs and considerably improve oyster production in oyster basins infected by pathogens. In addition, hybrids can exhibit daily growth increases of up to 30% compared to their parent strains. This aspect increases the interest in using resistant hybrids in oyster production basins. These resistant oysters obtained by hybridization can also make it possible to repopulate areas infected by pathogens, imported or not by humans through the cultivation of infected oysters, and to allow the restoration of a marine ecosystem. These resistant oysters obtained through hybridization can also help regenerate the biodiversity of strains cultivated in oyster ponds where inbreeding is becoming increasingly important. Inbreeding is a source of strain degeneration and a cause of the decline in productivity in oyster ponds. Other advantages may still become apparent to those skilled in the art upon reading the examples below given for illustrative purposes. EXAMPLES Example 1: Resistant oyster Ostrea edulis from the Diane pond in Corsica Wild oysters are collected from the Diane pond, a pond classified since the 1980s as contaminated by the parasites Bonamia ostreae and Martelias refringens, and successfully reproduced in a hatchery. The spat cultured at 0.2 g allows for an experimental production of excellent quality in the pond. This success allows the following conclusions to be drawn: - The absence of pathology up to marketing size in areas contaminated by Bonamia ostreae and Martelia refringens suggests resistance to parasitosis linked to a unique genetic polymorphism specific to the Corsican strain of the flat oyster Ostrea edulis. - Obtaining first batches of sizes No. 1 and No. 0 at 18 months from 0.2 g spat demonstrates the high growth potential of the Corsican strain. The duration of the breeding cycle is reduced by more than 50% compared to the duration of breeding Belon in the Atlantic. - The condition index is 16% (weight of edible flesh compared to the total weight), a level higher than that of the Belon from southern Brittany. The convincing taste tests confirm the remarkable quality of the Corsican strain from a commercial point of view. The strain's health status and resistance to pathogens were then tested. These tests were carried out according to the protocols prescribed by the OIE (World Organisation for Animal Health for bonamiosis and marteiliosis): - Cytological examination under the microscope of the tissue imprint of the cardiac ventricle or gills: no observation of small spherical or ovoid organisms of 2 to 5 pm inside the hemocytes after staining (Bonamia). - Histopathological examination under the microscope of tissue sections of Gills, digestive glands, gonads fixed and stained. No observations of parasitic cells of 2 to 5 pm in the free state or inside the hemocytes (Bonamia). No abnormality of the digestive gland, nor presence of spherical organisms of 20 to 30 pm attesting to the presence of Martelia. - Detection by immunofluorescence technique of monoclonal antibodies showing the resistance of the Corsican strain to the existence of Bonamia and Martelia parasites in the natural environment. - Polymerase chain reaction (PCR): no detection of Martelia refringens with the specific DNA probe targeting the ITS1 region of the parasite. - PCR-RFLP (Restriction fragment length polymorphism) analysis: negative control of DNA extracted from oyster tissues targeting the SSU rDNA fragment characteristic of the parasite Bonamia ostreae, attesting to the non-contamination of Corsican strains. - Molecular in situ hybridization (ISH) technique: probes specific to the DNA of Bonamia ostreae, SSU rDNA fragment, and Martelia refringens, ITS1 fragment, are brought into contact with histological sections of oyster tissues. Negative controls carried out by microscopic observation attest to the absence of B. ostreae and M. refringens in the tissues of the Corsican strain. These examinations show that the wild populations of flat oysters in the Diane pond are in contact with B. ostreae and M. refringens Bonamia and are not infected by these parasites in this natural environment. Artificial inoculation of these parasites was then carried out. - Corsican flat oysters were confined for several months in tanks cohabiting with oysters heavily contaminated by Bonamia ostreae. The oysters did not develop the disease and responded negatively to the detection tests described above. - Corsican oysters were injected into the mantle cavity with 50 μl of filtered seawater containing 5 x 106 viable Bonamia ostreae parasites isolated according to the method of Mialhe et al. (1988). Previously, the oysters were anesthetized by bathing with a 3.5% MgCl2-6H2O solution allowing the valves to open. After injection of the contaminating dose inoculum into the mantle cavity, the oysters were kept out of the water for one hour before being returned to the breeding tanks in seawater aerated by bubbling. After one month of breeding, no mortality was observed and the oysters responded negatively to the Bonamia ostreae detection tests described above. This experimental infection technique by bathing or injection into the mantle cavity cannot be used to test resistance to Martelia refringens, in the absence of direct horizontal transmission of this parasite. These experiments show that the wild Corsican-Sardinian flat oyster, from the Etangs de Diane, Urbino, gulfs of Porto Vecchio and Santa Manza, lagoons of Sardinia, is 100% resistant to the parasite Bonamia ostreae, a protozoan of the Haplosporidia family. These experiments carried out formally contradict the state of scientific knowledge, according to which the indigenous strain of Ostrea edulis would be decimated by a disease caused by a protozoan, the erroneous mentions appearing in the literature (MINICONI R., 2000, Les fruits de mer des côtes de Corse, Editions Alain Piazzola, P. 90 [9]) actually referring to breeding trials of imported spat from the Atlantic, which were not resistant and / or infected. The cross-checking of all the observations made on the Corsican flat oyster shows a resistance of the wild strain to haplosporidia, protozoa, martelias, parasites, opportunistic pathogens and external contaminating agents using the general mechanisms of cellular (hemocytes) and humoral immunity of bivalves, whose immune system remains non-adaptive, i.e. devoid of immune memory. Other wild populations of Mediterranean flat oysters were tested using the previous protocol and demonstrated complete resistance to the parasites Bonamia ostreae and Martelia refringens. These are the wild populations of Corsica, Morocco in the Nador lagoon, Tunisia in the Gulf of Gabès, Libya in the lagoons near the Tunisian border, and Greece. Example 2: Resistant oyster Ostrea Edulis from the Etang de Diane in Corsica. Wild oysters were collected from the Diane pond, an area contaminated by the pathogens Bonamia ostrae and Martelia refringens, and bred in a hatchery. Wild oysters are harvested directly from a natural site and are resistant to pathogens. The wild oysters collected are oysters which have a diameter greater than 60mm and which are at the age of first reproduction. Once the oysters have been collected, they are packaged in a container with a volume of 20 l, containing 20 litres of seawater with a salinity of 37%, a temperature of 13°C and a pH of 8.1 and sent to the hatchery. The collected oysters are marked before packaging using labels stuck with epoxy glue. Example 3: Non-resistant oysters In this example, a Belon quality oyster ('Quiberon' strain, South Brittany) from natural capture, with a size of 60 mm, which has not yet matured, was chosen. The oyster used to carry out the process of the invention is an oyster which does not express any pathologies. Example 4: Maturation of oysters for fertilization After collecting the oysters to be hybridized in examples 2 and 3, they are isolated and paired, i.e. a sensitive oyster is paired with a resistant oyster. Twenty pairs are thus formed. The pairs thus formed are placed in 20 previously filled tanks, each with a unit volume of 20 liters. Each tank has been previously filled with 20 liters of seawater with a salinity of 37%. The pH of the water is 8.1. The initial water temperature is 13°C, and brought to 20°C in fifteen days. The water is oxygenated by a pump system with an air flow of 20 l / h for each of the tanks. The water supply during maturation is carried out by a closed and isolated water circuit for each tank. The physicochemical characteristics of the water are kept constant throughout the maturation process. Oyster maturation is achieved over a period of 15 to 90 days by increasing the photoperiod from 9 hours to 15 hours and increasing the water temperature reaching levels of 20 to 30°C. During this maturation period, the nutrient inputs are made by adding unicellular algae of the strain Isochrysis galbana, Skeletonema costatum, Pavlova lutheri, Chaetoceros calcitrans, from the hatchery or refrigerated concentrated pastes from the company SATMAR to the medium. The input is made ad libitum, at a rate of three meals per day, as long as the oysters are feeding. The nutrient input is simultaneously supplemented by inputs of organic matter, notably from fish nursery pond waste. Maturation is verified by observing the stages of maturity of the gonads using techniques known to those skilled in the art under anesthetic bathing with magnesium chloride (MgCh) Gagnaire B., 2005, “Study of the effects of pollutants on the haemocyte parameters of the cupped oyster Crassostrea gigas - Interactions between environment, defence mechanisms and infectious diseases”, doctoral thesis from the University of La Rochelle, 412 pp.

[10] Oysters are mature for induction of gamete spawning when gonad maturation reaches stage 3. Example 5: Induction of gamete emission and fertilization of gametes The induction of gamete emission is carried out on oysters having undergone the maturation of example 4. The induction of gamete emission is carried out under the same conditions, using the same means and with the same pairs of oysters as in example 4. Prior to induction, water circulation is stopped to prevent the gametes from dispersing into the culture medium. Induction of gamete emission is achieved by thermal shock. The temperature is alternately lowered and increased by 4°C to 7°C at minimum values between 23°C and 30°C and maximum values between 30°C and 37°C. Males spawn first, which chemically induces the release of female gametes by female oysters. The sperm released into the environment are filtered by the female. Fertilization takes place in the female's mantle cavity, which incubates the larvae for eight to ten days before expelling them outside at a rate of about one million per female. During the incubation stage of the larvae in the mantle cavity, the water is recirculated. The larvae are fed with phytoplankton. The phytoplankton used to feed the larvae is composed of Isochrysis galbana, Pavlova lutheri, Chaetoceros forma pumilum, from mass cultures carried out in tanks located outside the hatchery, and supplemented if necessary with concentrated algae paste from the company SATMAR. The size of the phytoplankton used is 20 to 40 pm for the larvae in the early stages, 50 to 200 pm at metamorphosis up to the adult stage. The daily quantity of phytoplankton added to the medium is adjusted as desired, observing the filtration of the food inside the tanks, the water circulation being interrupted during meals. Example 6: Harvesting and fixing larvae The harvest of larvae released in a medium of example 5 is carried out using a sieve. The conditions for carrying out the harvest and the fixation of are identical to those of example 3. The sieve used has pores with a diameter of 120 μm. The use of the sieve makes it possible to harvest the larvae present in the culture medium. These are grouped into homogeneous batches according to their parents. The grouping is carried out in tanks having at the bottom micro-broken oysters and mussels crushed and calibrated on sieves between 250 μm and 500 μm. The volume of the tanks is 2 to 5 m3 The tanks are filled with water with a salinity of 37%, a pH of 8.2 and a temperature of 20 to 25 °C. The tanks, in a closed circuit, are oxygenated with a pump with an air flow of 2 to 5 m3 / h. After eight to ten days of incubation, the larvae are then attached to development supports. The method of fixing the larvae used is a classic method of fixing larvae on supports, notably described in the technical documentation of IFREMER, Ifremer, 2007, Aquaculture sheet of March 17, 2007, “Hatcheries: case of the cupped oyster”

[11] and in Helm, MM, 5 Bourne, N., Lovatelli, A., (comp. / ed.) Bivalve Hatcheries, A Practical Manual. FAO Fisheries Technical Paper No. 471. Rome, FAO. 2006. 184 p.

[12] Example 7: Resistant and non-resistant oysters 1 o The tables below represent other examples of resistant oysters and not resistant to the process of the invention; Table 1: Resistant O. edulis from the Mediterranean Table 2: Resistant O. edulis from the Mediterranean Table 3: Non-resistant O. edulis from the Mediterranean Table 4: Non-resistant O. edulis Table 5: other non-resistant Ostreidae Species Origin Strain location Status Ecological characteristics Stage Temperature Salinity Ostrea edulis Mediterranean CORSICA (Diane and Urbino) Wild Infralittoral Warm temperate Normal Ostrea edulis Mediterranean MOROCCO (Nador) Wild Mediolittoral Subtropical High Ostrea edulis Mediterranean LIBYA (lagoons) Wild Infralittoral Subtropical High Ostrea edulis Mediterranean TUNISIA (Gabès, Kerkennah) Wild Mediolittoral Subtropical High Ostrea edulis Mediterranean GREECE (Aegean Sea) Wild + farmed Infralittoral Warm temperate Normal Table 1: Resistant oysters Ostrea edulis from the Mediterranean Z / Species Origin Location Status Ecological characteristics Stage Temperature Salinity Ostrea edulis Mediterranean SPAIN, Murcia, Mar Menor) Wild Infralittoral Warm temperate Normal Ostrea edulis Mediterranean TURKEY (Anatolia, Bosphorus) Wild Infralittoral Temperate Ciiauuc Normal Ostrea edulis Mediterranean UKRAINE, Sevastopol, Crimea Wild + breeding Infralittoral Temperate Normal Ostrea edulis Mediterranean RUSSIA, GEORGIA, ROMANIA Wild Infralittoral Temperate Normal Ostrea edulis Mediterranean CROATIA, East Adriatic Wild Infralittoral Temperate Normal Ostrea edulis Mediterranean SPAIN, Balearic Islands, Minorca Wild Infralittoral Warm temperate Normal Ostrea edulis Mediterranean EGYPT, Alexandria & Wild Infralittoral Subtropical Variable Ostrea edulis Mediterranean France, Camargue, Port St Louis Wild Infralittoral Temperate Variable Table 2: Resistant oysters Ostrea edulis from the Mediterranean Species Origin Location of the strain status Ecological characteristics Stage temperature Salinity Ostrea edulis Mediterranean FRANCE, Thau, Languedoc Wild + breeding Infralittoral Warm temperate Normal Ostrea edulis Mediterranean ITALY, Venice, north Adriatic Wild + breeding Infralittoral Temperate Normal Table 3: Non-resistant oysters Ostrea edulis from the MEDITERRANEAN Species Origin Location of the strain status Ecological characteristics Stage temperature Salinity Ostrea edulis Atlantic FRANCE, Belon, southern Brittany Wild + breeding Mediolittoral Cold temperate Variable Ostrea edulis Atlantic FRANCE, Cancale, Manche Wild + breeding Mediolittoral Cold temperate Variable Ostrea edulis Atlantic SPAIN, Galicia Wild + breeding Mediolittoral Temperate Normal Ostrea edulis Atlantic PORTUGAL Wild + breeding Mediolittoral Temperate Normal Ostrea edulis Atlantic GREAT BRITAIN Wild + breeding Mediolittoral Cold temperate Variable Ostrea edulis Atlantic IRELAND Wild + breeding Mediolittoral Cold temperate Variable Ostrea edulis Atlantic NETHERLANDS Wild + breeding Mediolittoral Cold temperate Variable Ostrea edulis Atlantic DENMARK Wild + farmed Mid-littoral Cold temperate Variable Ostrea edulis Atlantic CANADA and USA (East) Wild + farmed Mid-littoral Temperate Variable Ostrea edulis Pacific CANADA, USA(West) Wild + farmed Mid-littoral Cold temperate Variable. Table 4: Non-resistant oysters Ostrea edulis from the Atlantic, PACIFIC and INDIAN Oceans Species Origin Strain location Status Exploitation status Ostrea denselamellosa Pacific CHINA, KOREA, JAPAN Wild + farming Endangered species Exploitation in decline Ostrea puelchana Atlantic BRAZIL, ARGENTINA Wild + farming Exploitation threatened in Argentina Ostrea folium Atlantic 0. Indian From MOROCCO to GABON, INDIA AUSTRALIA, MALAYSIA Wild + farming Experimental farms in Malaysia Ostrea permollis Atlantic WEST INDIES, USA (Florida, North Carolina) Wild + farming Ostrea stentina Atlantic 0. Indian AFRICAN COASTS + SOUTHERN MEDITERRANEAN Wild + farming Too small for commercialization Ostrea angasi Pacific AUSTRALIA Wild + farming Exploitation trials in Australia Ostrea conchaphila Pacific USA, CANADA (from California to Alaska) Wild + breeding Exploitation trials Tiostrea chilensis Pacific CHILE, NEW ZEALAND Wild + breeding Breeding in decline (parasites) Crassostrea virginica Atlantic CANADA and USA(East) Wild + breeding Parasitosis Breeding and exploitation in decline Crassostrea gasar Atlantic WEST AFRICA Wild + breeding Unsuccessful domestication attempts Crassostrea rhizophorae 0. Indian EAST AFRICA Wild + breeding Unsuccessful domestication attempts. Table 5: Non-resistant oysters of different genera or species of Ostrea edulis 8. Other examples of hybridization: The tables below show other examples within the framework of the present invention. Carrying out the hybridization of the invention allows the acquisition of resistance to pathologies, with a view to the sustainable exploitation of domestic oysters whose characteristics have been previously chosen in order to satisfy the physical, biological and commercial constraints of the breeding environments concerned. Table 6: examples of crosses for obtaining resistant oysters 10 according to the method of the invention. Oysters Ostrea edulis vulnerable to parasites Ostrea edulis ATLANTIC- EAST France Ostrea edulis THAU (France) Ostrea edulis VENICE Italy Ostrea edulis ATLANTIC- WEST Canada USA Ostrea edulis PACIFIC- EAST Mediterranean oysters resistant to parasites. Ostrea edulis CORSICA + + + + + Ostrea edulis MOROCCO + ? ? + + Ostrea edulis MURCIA ? ? + ? ? Ostrea edulis TURKEY ? ? + ? ? Table 6: examples of crossbreeding to obtain resistant oysters according to the method of the invention +: hybrids ?: not yet tested Oysters Ostrea edulis susceptible to parasites Ostrea edulis SOUTH BRITAIN Ostrea edulis CHANNEL Ostrea edulis GALICIA Ostrea edulis Portugal Ostrea edulis GREAT BRITAIN Ostrea edulis Ireland Ostrea edulis NETHERLANDS Ostrea edulis DENMARK Oysters resistant to parasites in the Mediterranean.___ Ostrea edulis CORSICA ? ? + + ? ? ? ? Ostrea eduiis MOROCCO + + ? ? + + + + Ostrea edulis MURCIA ? ? + ? ? ? ? ? ? ? Ostrea edulis BALEARIC ISLANDS ? ? + ? ? ? ? ? ? Ostrea edulis UKRAINE ? ? ? ? ? + + + + Ostrea edulis TURKEY ? ? + ? ? ? ? ? Table 6 (continued): examples of crossing to obtain resistant oysters according to the method of the invention + : hybrids ?: not yet tested The hybrids obtained by the process of the invention as presented above have particular characteristics acquired by this hybridization which meet the needs of traditional flat oyster production. The hybrids are resistant to bonamiosis and marteliosis. In addition, they are resistant to opportunistic pathogens. The hybrids have hardiness and tolerance to the amplitude of environmental variations, for example, flooding or submersion by tides, temperature, salinity. They have a high growth potential. They are suitable for cultivation in intertidal zones, in waters rich in nutrients and organic matter, and to the constraints of global warming of coastal waters. Finally, the hybrids are tolerant to anoxia, desiccation and transport constraints. Example 9: Hybridization between wild oysters from the ponds of Corsica and oysters from the Nador lagoon in Morocco. Wild oysters from the Corsican ponds and oysters from the Nador lagoon were crossed using the method of the invention. In this case, it is a cross between two resistant oysters. The proximity of Nador to the Strait of Gibraltar is the cause of tides that can reach two meters in the lagoon, causing temporary flooding of the natural Moroccan oyster beds. The hybridization of Diane oysters with those of Nador makes it possible to create hybrids that are resistant to lethal pathologies, with strong growth, adapted to the constraints of the tides encountered in the Atlantic, tolerant of increasing temperatures linked to global warming, and resistant to desiccation during dry transport for marketing. The production of hybrid spat was compared to that of Nador oyster spat produced simultaneously in a hatchery. The hybrid showed an average daily growth 30% higher than that of the control batch of Moroccan spat, in the month following metamorphosis. Furthermore, the relative sizes of domestic hybrid spat were much more homogeneous than those of the control, which appeared very heterogeneous. The heterosis effect (hybrid vigor) induced by controlled hybridization is thus confirmed in the context of the production of domestic flat oysters with high zootechnical potential. The domestic F1 hybrid thus created therefore responds to the problem of degeneration of the flat oyster "belon" in the shellfish basins of the Atlantic coast. 5 The very broad adaptations acquired by this hybridization according to the The process of the invention therefore meets the needs of traditional flat oyster production in Portugal, Galicia, Brittany, Normandy, Ireland, and the Netherlands. The hybrids are resistant to bonamiosis and marteliosis. They are also resistant to opportunistic pathogens. The hybrids are hardy and tolerant to tidal range and environmental variations, such as temperature and salinity. They have high growth potential. They are suitable for cultivation in intertidal zones (farming on foreshores), in waters rich in nutrients and organic matter (fining in abers, fining in claires), and to the constraints of global warming of coastal waters. Finally, the hybrids are tolerant to anoxia, desiccation, and transportation constraints, a resistance observed when sending packages from Corsica to Breton markets. List of references [1] Naciri-Graven et al. (1998) « Selecting the fiat oyster Ostrea edulis (L.) for survival when infected with the parasite Bonamia ostreae ». J.Exp. Mar Biol. Ecol.,224 :91-107. [2] N. Taris et al. “Genetic consequences of hatchery oyster larvae production: a study of drift and selection processes. » , Les actes du BRG, 6 (2006) 521-541. [3] Launey S. et al. « Géographie structure in the European fiat oyster (Ostrea edulis L.) as revealed by Microsatellite polymorphism ». J Hered. 2002 Sep-Oct;93(5):331-51 (2002). [4] Diaz-Almela et al. « Reduced female gene flow in the European fiat oyster Ostrea edulis ». J Hered. 2004 Nov-Dec;95(6):510-6. (2004). [5] Lannan JE, 1971, «Experimental self-fertilization of the Pacific oyster, Crassostrea gigas, utilizing cryopreserved sperm », Genetics, 68 : 599-601. [6] Bougrier and Ralbedomanana, 1986. “Cryopreservation of spermatozoa of the Japanese oyster,” Crassostreea gigas. Aquaculture, 58: 277-280. [7] Haffray et al. “Domestication and genetic improvement of fish stocks in the framework of SYSAAF”, INRA Prod. Anim., 2004, 17 (3), 243-252. [8] Gérard A., Naciri-Graven Y., Boudry P., Launey S., Heutebise S., Ledu C., Phelipot P., (1997). Control of gametogenesis in cupped and flat oysters. In: Natural and controlled reproduction of bivalves cultivated in France, Devauchelle N., Barret J., Salaun G., (1997), DRV / RA / RST 97-11, Ifremer Brest, 217 pp. [9] MINICONI R., (2000) Seafood from the coasts of Corsica, Editions Alain Piazzola, p 90.

[10] Gagnaire B., 2005, “Study of the effects of pollutants on the haemocyte parameters of the Pacific oyster Crassostrea gigas - Interactions between environment, defence mechanisms and infectious diseases”, doctoral thesis from the University of La Rochelle, 412 pp.

[11] Ifremer, 2007, Aquaculture sheet of March 17, 2007, “Hatcheries: case of the cupped oyster”.

[12] Helm, MM, Bourne, N., Lovatelli, A., (comp. / ed.) Bivalve Hatcheries, A Practical Manual. FAO Fisheries Technical Paper No. 471. Rome, 5 FAO. 2006. 184 p.

Claims

CLAIMS 1. Method for obtaining an oyster resistant to pathogenic agents, characterized in that it comprises the steps of: (a) provide a Mediterranean oyster Ostrea edulis resistant to said pathogens, b) supply an oyster not resistant to said pathogens from the Atlantic, Pacific and / or Indian Ocean chosen from Ostrea edulis, Ostrea angasi, Ostrea conchaphila, Ostrea lurida, Ostrea denselamellosa, Ostrea puelchana, Ostrea folium, Ostrea permollis, Ostrea stentina, Tiostrea chilensis, Crassostrea virginica, Crassostrea gasar and Crassostrea Rhizophorae of the opposite sex to said resistant Ostrea edulis oyster, (c) placing said oysters together in a tank containing water having a salinity permitting hybridization, d) maturation of said oysters in said tank, in increasing photoperiod with sufficient nutritional intake for said maturation, (e) induction of the emission of male gametes by means of an induction agent applied to oysters, f) fertilization of the female gametes by the male gametes emitted in step e), g) incubation of larvae for 8 to 10 days, h) feeding the larvae from step g) with phytoplankton so as to obtain eyed larvae, (i) harvesting the eyed larvae obtained, and j) fixing said larvae on a development support in order to obtain at least one oyster resistant to said pathogenic agents, in which steps e) to g) are carried out in vitro, the gametes being obtained by scarification of the gonads.

2. Method according to claim 1, in which said tank is continuously supplied by a circuit of said water and in which for the implementation of step e) said water circuit is interrupted.

3. Method according to claim 2, wherein said water circuit is isolated.

4. Process according to any one of claims 1 to 3, wherein the maturation in step d) is carried out at a temperature of 20 to 30°C.

5. A method according to any one of claims 1 to 4, wherein said tank is a hatching tank.

6. Method according to any one of claims 1 to 5, in which the induction means as defined in step e) is a thermal shock and / or at least one protein.

7. Method according to claim 6 in which the thermal shock is carried out by successively lowering and increasing the temperature to values between 5 and 55°C.

8. A method according to any one of claims 1 to 7, wherein said nutritional supply consists of live unicellular algae cultivated in a hatchery.

9. The method of claim 8, wherein the unicellular algae are selected from the group comprising Isochrysis galbana, Skeletonema costatum, Pavlova lutheri, Chaetoceros calcitrans, Tetraselmis sp.

10. Method according to any one of claims 1 to 9, in which step i) is carried out 8 to 10 days after expulsion of the larvae.

11. Method according to any one of claims 1 to 10, in which the development support of step i) is chosen from the group comprising micro-breaks and / or a sieved material between 250 and 500 pm.

12. A method according to any one of the preceding claims wherein the resistant Mediterranean oyster Ostrea edulis is of the age of first reproduction and has a diameter greater than 60mm.

13. Method according to any one of the preceding claims in which the resistant Ostrea edulis oyster and the non-resistant oyster are chosen at the end of the sexual rest period.

14. A method according to any one of the preceding claims wherein the hybridization takes place over a single breeding season.

15. A method according to any one of the preceding claims wherein the non-resistant oyster is a strain of oyster from the Atlantic, Pacific or Indian Ocean.