ABSTRACT
The production of cupped oysters is an important component of European aquaculture. Most of the production relies on the cultivation of the Pacific oyster Crassostrea gigas, although the Portuguese oyster Crassostrea angulata represents a valuable product with both cultural and economic relevance, especially in Portugal. The authors of the present study investigated the genetic diversity of Portuguese oyster populations of the Sado estuary, both from natural oyster beds and aquaculture facilities, through cox1 gene fragment sequencing. Then, a comparison with a wide dataset of cupped oyster sequences obtained from GenBank (up to now the widest available dataset in literature for the Portuguese oyster) was performed. Genetic data obtained from this work confirmed that the Pacific oyster does not occur in the natural oyster beds of the Sado estuary but showed that the species occasionally occurs in the oyster hatcheries. Moreover, the results showed that despite the founder effect and the bottleneck events that the Sado populations have experienced, they still exhibit high haplotype diversity. Risks are arising for the conservation of the Portuguese oyster reference populations of the Sado estuary due to the occurrence of the Pacific oyster in the local hatcheries. Therefore, researchers, local authorities, and oyster producers should work together to avoid the loss of this valuable resource.
ABSTRACT
Cells of the parasitic, unicellular eukaryote Ichthyodinium chabelardi were isolated from eggs of sardine (Sardina pilchardus) and from a previously unrecognized host, bogue (Boops boops), off the Atlantic coast of Portugal. Immediately after release from the infected fish egg or newly hatched larva, I. chabelardi cells were spherical and non-motile. After few minutes, spherical cells became flagellated and motile. Following 2-3 days of incubation and several divisions, spherical flagellated cells developed a twisted elongate shape and moved vigorously. Sequences of the small-subunit ribosomal RNA gene (SSU rDNA) were identical for I. chabelardi of both hosts and so were sequences of ITS1, ITS2 and the 5.8S rRNA gene. This genetic similarity suggests that eggs of sardine and bogue were infected by one single population of I. chabelardi. The SSU rRNA gene sequence of I. chabelardi was, in turn, 97% similar to those of two identical Asian isolates of Ichthyodinium sp. Phylogenetic analyses showed high support for the inclusion of Ichthyodinium in the so-called Marine Alveolate Group I (MAGI). Two morphologically well-described genera, namely Ichthyodinium and Dubosquella, have now been shown to belong to this group of seemingly exclusively parasitic alveolates.
