Reproduction

The wild breeders from the four targeted species can be collected at maturity in natural environments during the period preceding their reproductive season, but this period is limited to 2-3 months. It is an important aim of hatchery research to extend this period of reproductive maturity and thus to produce conditioned hatchery broodstock throughout the year by following controlled procedures.

Year-round artificial reproductive conditioning of oysters in commercial hatcheries is now relatively well understood, but the quality of the resulting gametes is still highly variable. However, for the mussels M. edulis/galloprovincialis and the clam R. decussatus, conditioning remains poorly controlled. The conditioning method for king scallop P. maximus requires improvement, specifically during the period after its natural spawning season, but this last point has been studied in another European project recently carried through called 'SETTLE' and thus it won't be considered in REPROSEED. However, strong links would be established between both projects.

Broodstock conditioning

In artificial reproduction, maintaining optimal environmental conditions is needed for best development of bivalve in hatcheries. Temperature and specific food diet for each species are also managed but for the European clam species, an effective broodstock conditioning methodology is still lacking. Moreover, food diet seems to have a major influence on R. decussatus maturation, food being a limiting factor for clams reproduction.

REPROSEED will study the influence of food quantity and quality on maturation and will establish quality indices based on the physiological condition of the wild broodstock and larval viability, during reproductive cycle. At a more basic level regulation of gene expression during initiation of gametogenesis in C. gigas will be investigated in relation with nutritional conditions.

Quality of gametes

A high variability in reproductive success is commonly observed in most bivalve hatcheries. It has been shown to be partly attributable to gamete quality and differential larval survival. The purpose of the present task is to improve the knowledge on gamete quality. We aim to determine the genes, the proteins and the signaling molecules involved in gamete maturation and to identify new markers of gamete quality.

REPROSEED will compare dissected and spawned gametes as well as their position in the genital ducts in oyster to understand processes of gamete maturation. Gamete quality will be assessed and genomic and proteomic approaches will be used to screen for markers of gamete quality. Knowledge gained will assist our understanding of gamete competence and lead to improve gamete quality and robustness of seed.

Gamete release

In oysters, the successive steps leading to spawning are clearly identified (Galtsoff, 1964). Spawning induction in both sexes has been achieved using various stimuli such as temperature shocks, but at the molecular level, aspects of its regulation have not been investigated tasks in other mollusc classes.

REPROSEED will investigate the effects of different spawning inducers to achieve better gametes release synchronization.