The effects of bioflocs in the diet of Pacific oysters Crassostrea gigas

Introduction and evaluation on the US West Coast of a new strain (Midori) of Pacific oyster (Crassostrea gigas) collected from the Ariake Sea, southern Japan

Reproductive cycles of the Pacific oyster Crassostrea gigas (Thunberg) from the Marlborough Sounds, New Zealand, were followed between June 1998 and January 2000. Histological examination of the gonad confirms an annual cycle with a winter inactive period followed by rapid gonad development and a single short spawning period. The population gonad index correlated with seawater temperature and changes in tissue dry weight, condition index, and biochemical components. In winter, few individuals with early gametogenic stages were present and rapid development of primary oocytes (diam. 11 μm) occurred during spring (September‐November). The developmental rate and the diameter of mature oocytes (37 μm) was similar for the 1998 and 1999 seasons. For a standard 110‐mm‐length oyster, maximal tissue body weight and condition index were recorded in December. Rapid weight loss in January was length dependent and was attributed to spawning. Temperature was the environmental variable which best correlated with the timing of gametogenesis. Food availability (phytoplankton biomass) may have been responsible for inter‐annual variations. The biochemical composition (% glycogen, lipid, protein) of separated gonad and somatic tissues were variable seasonally and annually. Gametogenesis (oocyte diameter) was associated with increased gonad protein and glycogen and a decrease in lipid concentrations. These changes are similar to those in Pacific oyster populations from other parts of the world.

BackgroundAlthough bivalves are among the most-studied marine organisms because of their ecological role and economic importance, very little information is available on the genome sequences of oyster species. This report documents three large-scale cDNA sequencing projects for the Pacific oyster Crassostrea gigas initiated to provide a large number of expressed sequence tags that were subsequently compiled in a publicly accessible database. This resource allowed for the identification of a large number of transcripts and provides valuable information for ongoing investigations of tissue-specific and stimulus-dependant gene expression patterns. These data are crucial for constructing comprehensive DNA microarrays, identifying single nucleotide polymorphisms and microsatellites in coding regions, and for identifying genes when the entire genome sequence of C. gigas becomes available.DescriptionIn the present paper, we report the production of 40,845 high-quality ESTs that identify 29,745 unique transcribed sequences consisting of 7,940 contigs and 21,805 singletons. All of these new sequences, together with existing public sequence data, have been compiled into a publicly-available Website http://public-contigbrowser.sigenae.org:9090/Crassostrea_gigas/index.html. Approximately 43% of the unique ESTs had significant matches against the SwissProt database and 27% were annotated using Gene Ontology terms. In addition, we identified a total of 208 in silico microsatellites from the ESTs, with 173 having sufficient flanking sequence for primer design. We also identified a total of 7,530 putative in silico, single-nucleotide polymorphisms using existing and newly-generated EST resources for the Pacific oyster.ConclusionA publicly-available database has been populated with 29,745 unique sequences for the Pacific oyster Crassostrea gigas. The database provides many tools to search cleaned and assembled ESTs. The user may input and submit several filters, such as protein or nucleotide hits, to select and download relevant elements. This database constitutes one of the most developed genomic resources accessible among Lophotrochozoans, an orphan clade of bilateral animals. These data will accelerate the development of both genomics and genetics in a commercially-important species with the highest annual, commercial production of any aquatic organism.

BackgroundDuring electricity generation of nuclear power plant, heat energy cannot be completely converted into electrical energy, and a part of it is lost in the form of thermal discharge into the environment. The thermal discharge is harmful to flora and fauna leading to environmental deterioration, biological diversity decline, and even biological extinction.ResultsThe present study investigated the influence of thermal discharge from a nuclear power plant on the growth and development of Pacific oyster Crassostrea gigas which is widely used as bio indicator to monitor environmental changes. The growth of soft part and the gonad development of oysters were inhibited due to thermal discharge. During winter season, temperature elevation caused by thermal discharge promoted the growth of oyster shells. During summer season, the growth rate of oysters in thermal discharge area was significantly lower than that of the natural sea area.ConclusionsThe results of this study provided a better understanding of assessing the impact of thermal discharge on the marine ecological environment and mariculture industry. It also provided a scientific basis for defining a safe zone for aquaculture in the vicinity of nuclear power plants.

First report of a putative involvement of the NMDA pathway in Pacific oyster (Crassostrea gigas) development: Effect of NMDA receptor ligands on oyster metamorphosis with implications for bivalve hatchery management

Triploidy was induced in the Pacific oyster Crassostrea gigas by treating newly fertifiized eggs with cytochalasin B in July 1987 and 1988. Growth, survival, glycogen content, and moisture content of triploid oysters cultured in the waters of Hiroshima were investigated. In the spawning season (July to September) shell height, total weight and soft body weight of diploids decreased or failed to increase, while those of triploids continued to increase. At the end of September the mean values of shell height, total weight and soft body weight of triploids were 1.0 to 1.2, 1.4 to 1.9, and 1.8 to 2.5 times respectively as much as those of diploids. The difference of soft body weight between diploids and triploids suggests that diploids lost 44 to 60% of wet soft body weight or 56 to 67% of dry soft body weight as gametes spawned. Condition index, which means the ratio of soft body weight against total body weight including shells, decreased sharply in diploids in the spawning season owing to mass spawning, while this sharp decrease was not observed in triploids. In diploids, the moisture content of the soft body, which was around 80% before the spawning season, increased 83 to 84% in the spawning season. But in the case of triploids, moisture content was at a low level of 77 to 82%. The glycogen content of diploids decreased to a low level of 2.7 to 5.4% on a dry basis according to gametogenesis, while that of triploids was at a high level of 8.5 to 16.9%. These results are due to the retardation of gonado- and gametogenesis. Mortality of triploids was about half of diploids from September to November, which suggests that the decrease in physiological activities must be smaller in triploids than in diploids because of the retardation of gonado- and gametogenesis.

The Pacific oyster Crassostrea gigas was introduced in northwestern Mexico for aquaculture purposes. Although its cultivation has been successful, this species has shown high mortalities during summer. To mitigate this problem, producers have resorted to biotechnology (triploidy), whose performance -regarding diploid seedling- depends on site conditions and stocking time. Hence, uncertainty exists on its benefits under real production conditions. This research evaluates triploidy performance by implementing a dynamic simulation model considering environmental effects (temperature and chlorophyll) on culture production. The dynamic simulation was based on systems theory, dividing the productive system into two sub-models (environmental and biological), including temperature and chlorophyll effects, growth, mortality, and condition index parameterized in the function of the environmental parameters. The dynamic simulation results suggest that implementing triploid culture is advantageous in zones under high stress associated with high temperature and low productivity; likewise, triploid spat tends to show better performance independently of the site. Nevertheless, performance by ploidy varies depending on the environmental conditions of the sites.

This study investigates the vulnerable period in postspawning Pacific oysters (Crassostrea gigas) through physiological and immunological assessments. After spawning, the oyster condition index reduced by 50% and required 70 days to recover to the prespawning level. The mantle glycogen reduced quickly while the reduction in tissue protein occurred slowly. The mantle tissue also lost more protein than gills. The analysis of adenylate energy charge indicated that oysters were stressed in the first 8 days after spawning. As a result of spawning, haemocyte phagocytosis was reduced and remained at a low level for 3 days. In contrast, the reduction of haemolymph antimicrobial activity did not occur until 3 days after spawning and continued to decline until day 8. This immunesuppression was not directly correlated to the changes in haemocyte density. Our study suggests that the first 8 days after spawning are a critical period for oyster survival due to the loss of energy and low immunity. This study further improves our understanding of the coincidence between spawning and summer mortality in oyster aquaculture.

Genome-wide analysis of the cytochrome P450 gene family in Pacific oyster Crassostrea gigas and their expression profiles during gonad development

Simple SummaryThis study reveals the expression profiles of lncRNA in the gonads of the Pacific oyster Crassostrea gigas. The potential function of lncRNAs was predicted in the case of antisense and cis-regulatory mechanisms based on their physical positions and their coexpression relationships in the case of trans regulation. Sterility-related DEGs and DELs were chosen for subsequent analysis, demonstrating that trans-regulatory lncRNAs might play a vital role in the gametogenesis of C. gigas. We constructed core networks of lncRNAs–mRNAs for triploid sterile females and hermaphrodites based on pathway results, in which 28 lncRNAs and their 54 trans-regulatory genes were detected. Among 28 sterility-specific lncRNAs, MSTRG.79882.3 and MSTRG.79882.4 for triploid sterile females and MSTRG.33704.1, MSTRG.63844.1, and MSTRG.5675.1 for hermaphrodites play the most significant role.Long noncoding RNA (lncRNA), a type of non-protein-coding transcript, is emerging as a crucial regulator of gene expression. However, few roles of lncRNA in the reproductive process of the Pacific oyster (Crassostrea gigas) have been defined, especially in the regulatory mechanism of sterile triploids gametogenesis. To uncover the potential role of lncRNA, the gonads of diploids, sterile triploids, and partially sterile triploids underwent RNA sequencing. A total of 9618 reliable lncRNAs were identified. The target relationship between lncRNA and mRNA was predicted based on cis, trans, and antisense regulation with bioinformatic software. We chose differentially expressed lncRNAs and mRNAs when sterile triploids were compared to partially sterile triploids and diploids for subsequent functional enrichment analysis. Findings revealed that trans-regulatory lncRNAs might play a significant role in the gametogenesis of C. gigas. Combining pathway results, we constructed core networks of lncRNAs–mRNAs for triploid sterile females and hermaphrodites. Fifty-four genes related to cell division, germline-cell maintenance, and glycogen metabolism were found to be associated with sterility. A total of 28 candidate lncRNAs were predicted to trans-regulate these genes. We speculated that MSTRG.79882.3 and MSTRG.79882.4 for triploid sterile females and MSTRG.33704.1, MSTRG.63844.1, and MSTRG.5675.1 for hermaphrodites were highly important as they were predicted to regulate more sterility-specific genes than others. Our work collectively identified sterility-related lncRNAs and implicated the potential mechanism of lncRNA-mediated regulation in the gametogenesis of sterile triploid oysters.

64. Comparative cryopreservation study of trochophore larvae from two species of bivalves: Pacific oyster (Crassostrea gigas) and blue mussel (Mytilus galloprovinciallis)

Since the late 1990s, the Pacific oyster (Crassostrea gigas) has spread into the East Frisian Wadden Sea (Germany). This invasion provided an opportunity to study the population dynamics and the patterns of spread during the initial bioinvasion process. With its source area in The Netherlands, the bioinvasion continues in an eastward direction, as documented by a gradient of high abundances in the west and low abundances in the east during the first study year. One year later, abundances of the Pacific oyster were more heterogenic and differed between adjacent tidal basins. The increase in population sizes at all study sites was very high, reaching levels similar to native occurrence populations. The growth constant (K) varied between 0.300 and 0.990 year−1. The mussel bed with the highest densities had a mean abundance of >300 ind. m−2, and a maximum of 1,460 ind. m−2. Furthermore, the bioinvasion was facilitated by a low mortality (Z) found for populations between 0.5 and 1.5 years old (Z = 0.03–0.13 year−1). At present, Pacific oysters are well established at several locations in the East Frisian Wadden Sea and may become with these reproductive potential self-sustaining populations.

Nutritional contribution of seaweed Ulva lactuca single-cell detritus and microalgae Chaetoceros calcitrans to the growth of the Pacific oyster Crassostrea gigas

Proteomic identification of protein associated to mature spermatozoa in the Pacific oyster Crassostrea gigas

Norgestrel shows androgenic properties and triggers reproductive neuroendocrine toxicity in the testes of Pacific oysters (Crassostrea gigas).