Comparison of the growth of the eastern oyster Crassostrea virginica (Gmelin) in low and high salinity and its relationship with the turbellarian Urastoma cyprinae (Graff) (French and English text)

The Turbellarian Urastoma cyprinae (Graff) occurs on the gills of various bivalves species, including the mussel Mytilus galloprovincialis, where it is known to cause serious damage. More recently, it has been shown that the worms are strongly attracted to the gills of the American oyster (Crassostrea virginica) and are capable of inducing changes to the composition of the proteolytic enzyme of the host mucus. Such changes may be attributable to secretory products released by the worms. This work attempts to gain a better appreciation of the secretory structures associated with the worm tegument, focusing primarily on the widespread mucous and rhabdoid glands. Mucous glands assume different forms and consist of minute spherules tightly bound together that range between 0.7 and 0.9 μm in diameter. The glands occupy a volume of approximately 20% of the body cavity and are the most voluminous secretory organs in the worm. The considerably smaller rhabdoid glands are unevenly distributed throughout the peripheral parenchyma and contain secretory granules ranging in form and size between 0.35 and 1.2 μm in diameter. The latter occur most prominently along the distal margins of the epithelium. The frontal pole of U. cyprinae consists of a complex assembly of mucous and rhabdoid gland cells as well as other glandular structures. Collectively, these bodies release their contents to the outside via a network of narrow channels. The overall organization is consistent with the frontal gland previously described for other free living Turbellarians such as the Rhabdocoeles.; Aside from any damaging effects to oysters, the aesthetic impact on consumers due to the presence of the worms on the gills, may have a negative impact.; Depuration methods for the elimination of microbial organisms or toxic products are used extensively in aquaculture. Furthermore, information related to salinity tolerance has previously been combined with depuration techniques to eliminate unwanted organisms from commercially important finfish and shellfish species. Interestingly, this parasite is absent in low salinity waters of the Atlantic coast. The current work take into consideration the above approach by focusing on salinity tolerance levels of U. cyprinae as a possible means of eliminating the gill worms from oysters. (Abstract shortened by UMI.)...