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Reproduction de la palourde Ruditapes decussatus, en milieu naturel (sud Tunisie) et en milieu contrôlé (écloserie expérimentale) : relation avec le système immunitaire

Abstract : The aim of this study was to describe and compare the gametogenic activity of Ruditapes decussatus in situ and in hatchery. Criteria of maturity were characterized and the positive role of conditioning in the success of artificial reproduction was underlined. Specimens sampled in the South of Tunisia were conditioned at the experimental station of Monastir (Tunisia). The parameters studied were the variation of the condition index and the frequency distribution of oocyte diameters. Results showed that the reproductive cycle was continuous in situ. Gametogenesis started in January and February. Gonadic activity increased from March to November – December. Spawning events occurred irregularly from June to December. In winter conditioning, mature oocytes were produced from March and spawning began in April. The increase in temperature and food abundance shortened the gametogenesis duration; ripe gametes were produced two months earlier compared to natural environment. In summer conditioning, the reproductive cycle was the same as that in the natural site, maturation and spawning occurred simultaneously. In bivalves, the blockage of oocytes at prophase I is released only during the egg-laying period. The second blockage occurs during metaphase I and is released by fertilization. In the case of the venerid Ruditapes decussatus, when we dissect the gonad we obtain oocytes which are blocked at prophase I and so cannot be fertilized. In order to release this blockage, we used serotonin (5-HT). This study is the first to scrutinise the maturation of oocytes induced by serotonin in R. decussatus. We have thus demonstrated that adding 20 µM of serotonin in an external application allows the recovery of meiosis and the passage of oocytes from germinal vesicle (G.V.) to germinal vesicle break down (GVBD) in approximately 90 minutes at a temperature of 20°C. The highest percentage of oocytes obtained in GVBD was 67%. We have also evaluated the competence of oocytes in GVBD during fertilization, and found the greater the degree of reproductive condition, the higher is the percentage of oocytes that can undergo GVBD. From an estimated threshold of 53% of oocytes capable of GVBD, broodstock placed in a controlled environment are liable to spawn when they undergo thermal shocks. This allows us to consider this percentage as a criterion for the evaluation of oocytes during fertilization
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Submitted on : Monday, June 20, 2005 - 11:53:34 PM
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Leila Hamida. Reproduction de la palourde Ruditapes decussatus, en milieu naturel (sud Tunisie) et en milieu contrôlé (écloserie expérimentale) : relation avec le système immunitaire. Immunologie. Université de Bretagne occidentale - Brest, 2004. Français. ⟨tel-00009544⟩

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