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The production of Venerupis decussata relies on wild seed collection, which has been recently compromised due to recruitment failure and severe mortalities. To address this issue and provide an alternative source of seed, artificial spawning and larval rearing programs were developed. However, hatchery-based seed production is a relatively new industry and it is still underdeveloped. A major hurdle in the European clam seed production is the control of spawning and reproduction, which is further hindered by the impossibility of obtaining fertile gametes by gonadal “stripping”, as meiosis re-initiation is constrained to a maturation process along the genital ducts. In the present study, oocytes were collected from 15 females and microarray analyses was performed to investigate gene expression profiles characterizing released and stripped ovarian oocytes. A total of 198 differentially expressed transcripts between stripped and spawned oocytes were detected. Functional analysis carried out on these transcripts highlighted the importance of a few biological processes, which are most probably implicated in the control of oocyte competence. Significant differences were observed for transcripts encoding proteins involved in meiosis progression (e.g. dual specificity phosphatase CDC25), WNT signalling (e.g. frizzled class receptor 8, wingless-type MMTV integration site family member 4), steroid synthesis (e.g. progestin and adipoQ receptor family member 3, cytochrome P450-C17), mRNA processing (e.g. zinc finger protein XlCOF28), calcium regulation (e.g. regucalcin, calmodulin) and ceramide metabolism (ceramidase B, sphingomyelinase). This study provides new information on transcriptional profiles putatively associated with ovarian egg infertility, and suggests potential mechanisms regulating early oocyte development in clams. Genes which were differentially expressed between stripped and spawned oocytes might have a pivotal role during maturation process in the gonadal duct and could be interesting targets for further functional studies aiming to make ovarian oocytes fertilizable. [ABSTRACT FROM AUTHOR]

The clam Ruditapes decussatus is commercially important in the south of Portugal. The random amplified polymorphic DNA (RAPD) technique was applied to assess the genetic diversity and population structure of two Portuguese populations occurring in the Ria Formosa (Faro) and the Ria de Alvor, respectively. Twenty-five individuals of each population were investigated by RAPD profiles. Genetic diversity within populations, measured by the percentage of polymorphic loci ( %P), varied between 68.57% (Alvor) and 73.88% (Faro). Shannon's information index ( H) and Nei's gene diversity ( h) were 0.281 and 0.176, respectively, for the Alvor population and 0.356 and 0.234 for the Faro population. Overall, genetic variation within R. decussatus populations was high. The total genetic diversity ( H) was explained by a low variation between populations ( G = 0.145), which is consistent with high gene flow ( N = 2.9). The analysis of molecular variance (AMOVA) showed that 65% of variability is within populations and 35% between populations (Φ = 0.345; P ≥ 0.001). The value of Nei's genetic distance was 0.0881, showing a low degree of population genetic distance, despite the different geographic origin. This is the first study on the population genetics of R. decussatus by RAPD technique. The results may be useful for restocking programs and aquaculture. [ABSTRACT FROM AUTHOR]

Successful larval growth and development of bivalves depend on energy derived from internal (endotrophic phase) and external (exotrophic phase) sources. The present paper studies survival, growth and biochemical changes in the early developmental stages (from egg to pediveliger) of the clam Ruditapes decussatus in order to characterize the nutritional requirements and the transition from the endotrophic to the exotrophic phase. Three different feeding regimes were applied: starvation and two mono-specific microalgal diets ( Isochrysis aff galbana and Chaetoceros calcitrans). A comparison between fed and unfed larvae highlighted the importance of egg lipid reserves, especially neutral lipids, during a brief endotrophic phase of embryonic development (first 2 days after fertilization). Egg reserves, however, may energetically contribute to the maintenance of larvae beyond the embryonic development. In fed larvae, the endotrophic phase is followed by a mixotrophic phase extending to days 5-8 after fertilization and a subsequent exotrophic phase. Metamorphosis starts around day 20. The intense embryonic activities are supported by energy derived from lipids, mainly from neutral lipids, and the metamorphic activities are supported by energy derived essentially from proteins accumulated during the planktonic phase and depend on the nutritional value of diets. The diet of I. aff galbana proves to be more adequate to R. decussatus larval rearing. The results provide useful information for the successful production of R. decussatus aquaculture. [ABSTRACT FROM AUTHOR]

Abstract: The carpet shell, Ruditapes decussatus is a species with a high commercial importance in Portugal and other Southern European countries. However, high growth rate variability is a major problem in the aquacultural production of this species. The objective of this work was then to study the possible differences between fast-, medium- and slow-growing individuals at three times of sampling, of a same cohort of R. decussatus in terms of eventual numerical chromosomal changes, aneuploidy, but also the level of physiological capacity, by assessing the condition index and the biochemical composition: proteins, total lipids, neutral lipids, phospholipids, carbohydrates, free reducing sugars, polysaccharides and total energy. Hypoploid cells of 2n=37, 36, 35 or 34 were observed in all groups of individuals. The aneuploidy values observed ranging from 19% to 79%, were substantially higher than those observed in previous studies for other bivalve species. The differences in the observed aneuploidy between fast- and slow-growing clams were highly significant and a negative correlation was also observed between the level of aneuploidy and length. In general, the synthesis of the evaluated biochemical components showed no significant differences among groups suggesting that this synthesis could be related to extrinsic factors or that the analyzed biochemical components were not specific to detect the lack of certain aminoacids and enzymes involved in growth. The only exception was for total lipids, which were significantly lower in the medium and slow growing groups relative to the fast growing group. The evaluation of the relationships between all the studied parameters was performed through a principal component analysis (PCA). The results of this study demonstrate the existence of a negative correlation between somatic aneuploidy and growth in the carpet shell, as previously reported for other bivalve species. Moreover, for the first time in this study, this negative correlation is confirmed over time in a same cohort of the clam R. decussatus. [Copyright &y& Elsevier]

Abstract: Aneuploidy is a cytogenetic phenomenon known as an abnormal diploid chromosome number. A negative relationship between growth rate, one of the biggest problems faced by bivalve producers, and this phenomenon was already verified for two oyster species, the Japanese oyster Crassostrea gigas, the Portuguese oyster Crassostrea angulata and their interspecific hybrids and, more recently, in the carpet shell clam Ruditapes decussatus. The main objective of this study was to assess whether chromosome losses in aneuploid situations could be explained by differential chromosomal susceptibility, as previously reported in the oyster C. gigas. Thereby, we applied the restriction enzyme (RE) digestion chromosome banding technique to aneuploid karyotypes of R. decussatus and C. angulata, in order to identify the missing chromosomes. The results of this study showed that 4 out of the 19 chromosome pairs (viz. 1, 6, 12, and 19) of R. decussatus and 3 out of the 10 chromosome pairs (viz. 1, 9, and 10) of C. angulata were preferentially affected by the loss of one homologous chromosome. The chromosomal loss in C. angulata was very similar to the one previously observed in C. gigas. These results open a new field for further research in order to have a better understanding of the aneuploidy phenomenon in bivalves and particularly its negative relationship with growth rate. [Copyright &y& Elsevier]