Data/hora: 01/06/2024 04:32:20

Provedor de dados: 	5	
País: 	France	
Título: 	Conditionnement artificiel de l'huître Crassostrea gigas	
Autores: 	Jorge Eduardo, Chávez Villalba.	
Data: 	2001-11-26	
Ano: 	2001	
Palavras-chave: 	Water temperature; Biochemical studies; Gametogenesis; Breeder conditioning; Larval rearing.	
Resumo: 	In France, 90% of the annual cup oyster (Crassostrea gigas) production comes from larvae caught in the Arcachon and Marennes-Oléron basins. However, the spat catch shows many interannual irregularities and oyster farmers increasingly say they need spat outside of the reproductive period. Thus, the role of hatcheries in Japanese oyster spat production in France is becoming increasingly evident. However, the current state of knowledge about cup oyster reproduction in controlled conditions is limited, and hatchery professionals must confront various problems to optimise treatment of genitors so as to obtain larval breeds in good health and a lengthening of the reproductive season. To respond to this, we have carried out a study on three aspects that seem fundamental: i) the inability to produce viable gametes and larvae during a refractory period, known as "sexual repose", that takes place in the fall in our part of the world; ii) the lack of knowledge of the effect of environmental parameters on the gametic development of C. gigas in the laboratory, among which are temperature and the circadian light cycle; iii) the influence of the reproducer's place of origin (what is their physiological state?) used for the gamete production and the impact of the season during which the experiments are performed. These studies have made it possible for us to establish that the internal clock that regulates gametogenesis in C. gigas can be modified by the influence of environmental factors, in particular by temperature. In this way, the production of viable ovocytes and larvae is possible during this species' period of "sexual repose". The resumption of gametogenesis occurs when the temperature is again in a decreasing phase, approximately at 12o C, and we have observed that the circadian light cycle does not play a major role in the resumption of gametic activity. Studying several different batches of animals from the Atlantic coast (Bay of Les Veys, Aber Benoît, Baden, Bouin, La Tremblade and Arcachon) enabled us to observe that oysters display a very significant adaptation to the environmental conditions peculiar to each farming site, and that this adaptation is not of genetic origin since the oysters used in our research were all caught in the same locality (Arcachon basin). This adaptation is expressed as well by a different response from the oysters of each region to treatment experiments in the laboratory. The individuals from the most northerly regions, Bay of Les Veys and Aber Benoît, have a greater stock of reserves and show the best performance in the laboratory: A higher proportion of mature ovocytes at the end of the treatments and a greater production of ovocytes after scarification of the gonad. The biochemical study showed that the oysters from the Bay of Les Veys use glucides as gametogenesis support, while those from the south (La Tremblade), besides the glucides, use their proteins as the main source for the development of the ovocytes. The oysters from the Bay of Les Veys and Aber Benoît kept without food show a gametogenetic evolution identical to that of the animals that were fed. Nonetheless, the oysters that were fed produce significantly more ovocytes than the ones that were not fed. It seems that the quantity of ovocytes produced in artificial conditions depends directly on the food offered during treatment. However, for larval breeding, there are no significant differences in the larval yield rates ("D" larvae) between the batches of fed and the non-fed oysters. Thus, the quality of the ovocytes seems linked not only to the quantity and the quality of the food provided during the treatment, but also to the quantity and quality of reserves accumulated by the oysters during their stay at sea. The resumption of C. gigas' gametogenesis seems to respond to two factors: the availability of food and a minimal temperature specific to each batch of oysters that can vary according to the geographical location. The results of our study indicate that C. gigas in France shows a flexible reproductive cycle that adapts to the various environmental conditions found in each farming site and that it is these conditions that regulate the onset and duration of each batch's gametogenesis.	
Tipo: 	Text	
Idioma: 	Francês	
Identificador: 	http://archimer.ifremer.fr/doc/2001/these-1456.pdf	
Editor: 	Université de Bretagne Occidentale	
Relação: 	http://archimer.ifremer.fr/doc/00000/1456/	
Formato: 	application/pdf