Insights on the association between somatic aneuploidy and ostreid herpesvirus 1 detection in the oysters Crassostrea gigas,C. angulata and their F1 hybrids

Cytogenetic abnormalities associated with viral infections, including from viruses of the Herpesvirales order, have been reported in vertebrate species. Ostreid herpesvirus 1 (OsHV‐1) has been detected worldwide during mortality outbreaks of the Pacific oyster Crassostrea gigas. On the other hand, a high proportion of aneuploid cells in somatic tissues have been observed in C. gigas. In this study, we analysed the putative association between aneuploidy levels and the detection of OsHV‐1 in gills of C. gigas, the Portuguese oyster C. angulata and their F1 hybrids cultured in Ria Formosa (Portugal). OsHV‐1 was detected by PCR in 5.4% of the total of oysters analysed (n = 111) namely in 11.1%, 8.0% and 1.7% of C. gigas, C. angulata and F1 hybrid respectively. Sequencing analysis of a viral fragment amplified with the C2/C6 primer pair revealed a high similarity with the OsHV‐1 reference type. Moreover, in situ hybridization confirmed the presence of OsHV‐1 in gill tissue. Oysters where OsHV‐1 was detected had a significantly higher mean percentage of aneuploid cells (25%) than the ones where the virus was not detected (18%). However, the overall low percentage of positive samples contrasted with the high mean percentage of aneuploidy observed, with 50% of the oysters analysed showing a percentage of aneuploid cells between 20% and 30%. We hypothesize that somatic aneuploidy may adversely affect oysters making them more prone to OsHV‐1 infection, but the virus is unlikely to be the cause of somatic aneuploidy.     

Is fertility of hybrids enough to conclude that the two oysters Crassostrea gigas and Crassostrea angulata are the same species?

The distinction of the two cupped oysters Crassostrea gigas (Thunberg, 1793) and Crassostrea angulata (Lamark, 1819) into two species was chiefly due to their differing geographical distributions, C. gigas being present in Asia and C. angulata in Europe. Today it is commonly accepted that C. angulata and C. gigas are a single species according to morphological, genetic and F1 hybridization data. However, the demonstration of the fertility of their hybrids and the absence of any reproductive isolation remained to be investigated. Consequently, we studied the fertility of hybrids and sperm competition by performing three different experiments and producing G1 and G2 hybrid progenies between wild populations of C. angulata and C. gigas. Progenies showed very close developmental yields, at 24 hours after fertilization, according to dam taxa suggesting a strong maternal transmission of oocyte quality, but no reproductive isolation was observed between the two taxa. Significant decreases of developmental yields were noticed in C. angulata females with sperm competition, most probably due to early larval mortality. The fertility of hybrids C. angulata × C. gigas was demonstrated, which is further evidence that they are the same species. To definitively state the precise taxonomic classification of C. angulata and C. gigas, further studies are needed to (i) identify geographical zones where these taxa are in contact and (ii) assess their level of hybridization in these zones.     

Phenotypic trait of Crassostrea hongkongensis♀× C. angulata♂ hybrids in southern China

The Hong Kong oyster (Crassostrea hongkongensis) and the Portuguese oyster (Crassostrea angulata) are important aquaculture species in southern China. To understand the potential feasibility of hybridization between the two species, two‐by‐two factorial cross‐experiments were conducted in Shenzhen (Guangdong province). An asymmetry in fertilization was revealed: C. hongkongensis eggs could be fertilized by C. angulata sperm, but the reciprocal cross was not possible. The fertilization and hatching success in the C. hongkongensis females × C. angulata males (HA) cross was lower than the two intraspecific crosses. Moreover, hybrid larvae had a slower growth rate than those from parental progenies due to genome incompatibility. However, the size of the spat and adult growth were greater than those of the two parental progeny, with obvious heterosis during the grow‐out stage. The survival advantage of hybrids was examined at all times. The surprising finding was that all hybrids were completely fertile, meaning they could produce normal and functional gametes. Genetic analysis by molecular markers was applied to confirm that the HA spat were true hybrids. Our results revealed that the interspecific hybridization between C. hongkongensis and C. angulata is completely successful in one direction. Furthermore, hybrids are viable, fast growing and completely fertile, which provides a promising method for the genetic improvement of oysters as a new aquaculture stock in southern China.     

Mitochondrial DNA barcoding for Okinawan oysters: a cryptic population of the Portuguese oyster Crassostrea angulata in Japanese waters

We used mitochondrial (mt) DNA barcoding to evaluate the species diversity of oysters sampled from the coast of Okinawa Island, Japan. Our analysis revealed the presence of a hitherto-unrecognized population of the Portuguese oyster Crassostrea angulata, a putative species closely related to the Pacific oyster C. gigas. Forty-eight Okinawan oyster specimens were collected and subjected to species diagnosis trials based on mtDNA barcodes. Of the 30 Crassostrea specimens, 17 were identified as C. angulata, seven as C. gigas and six as C. bilineata (syn. C. iredalei). The remaining 18 Saccostrea specimens formed several divergent clades in phylogenetic trees, although they could not be identified to species level because of the confounding taxonomy of the Saccostrea species complex. Our results stress the necessity for reviewing the species diversity of Okinawan oysters.     

The effects of dietary supplements of polyunsaturated fatty acid on pearl oyster,Pinctada margaritifera L., gonad composition and reproductive output

Black‐lip pearl oyster, Pinctada margaritifera broodstock was collected from the wild. Egg production, hatching rate and larval development were compared between oysters induced to spawn within 2 days after collection in the wild (T1), oysters fed a pure microalgae diet during 24 days before spawning (T2) and oysters fed the same microalgal diet in which 10% of the algae were replaced with 2 μm polyunsaturated fatty acid (PUFA)‐rich microspheres (T3). Administration of lipid microspheres resulted in larger sized eggs, a higher percentage of D‐larvae and larger sized 48‐h‐old larvae (P<0.05). The total and neutral lipid contents of the gonad increased after oysters were fed with microalgae only or with supplementary diet. The major neutral and polar fractions of saturated fatty acid (SFA) were 16C and 18C fatty acids, and not influenced by the diet (P>0.05). The gonads of oysters fed supplementary PUFA contained more docosahexaenoic acid (DHA) and less monounsaturated fatty acids. Higher level of DHA in gonads of T3 was associated with oogenesis and embryogenesis success. The n‐3/n‐6 ratio in the neutral lipid fraction provides a good indication of the spawning condition and predicting egg size and hatching rate.     

The effect of temperature on physiological energetics of a fast‐growing selective strain and a hatchery population of the Pacific oyster (Crassostrea gigas)

Growth is an important aquaculture trait, which has been one of the most important traits for genetic improvement in aquatic species. Numerous fast‐growing domesticated aquaculture organisms are being cultured, but the physiological processes underlying growth remain largely unexplored. The Pacific oyster (Crassostrea gigas) is one of the most widely farmed bivalves. In order to improve the productivity traits, a fast‐growing selective strain of C. gigas was established. In this study, we compared physiological energetics of the fast‐growing selective strain and an unselected hatchery population of C. gigas under different conditions of temperature. Components of energy gain (clearance rates, ingestion rates, absorption efficiency and absorption rates), energy loss (metabolic rates) and resulting energy budget (scope for growth) were analysed at four temperatures (15, 20, 25 and 30°C). The results indicated that selective breeding oysters had a higher energy gain compared to unselected oysters, but the selected strain and hatchery population of oysters did not significantly differ in metabolic rates at all tested temperatures (p > 0.05). The enhanced energy gain resulted in almost two times higher scope for growth in selective breeding oysters compared with unselected oysters. Physiological characteristics of C. gigas were greatly affected by temperature and showed a fluctuation with the increase in temperatures. The selective breeding oysters outperformed those of hatchery population in growth performance by an increased energy gain along with a similar energy loss. This study provided insight into physiological energetics accounting for growth improvements in fast‐growing selective strain of C. gigas.     

Broodstock conditioning of the Portuguese oyster (Crassostrea angulata,Lamarck, 1819): influence of different diets

The Portuguese oyster Crassostrea angulata shows great potential in oyster farming. The conservation of pure populations of this species is important for production diversification and biodiversity preservation. In this way, the zootechnological development for seed hatchery production is extremely important. Broodstock conditioning is a key step in the process of rearing bivalves in a hatchery. Many factors regulate the reproductive cycle, being food one of the most important ones. To evaluate the effect of different diets on C. angulata reproductive performance, broodstock were conditioned with different food regimes formulated fundamentally by flagellates (Diet 1 – Pavlova lutheri and Isochrysis galbana clone T‐ISO; Diet 2 – P. lutheri, T‐ISO and Skeletonema costatum) and constituted fundamentally by diatoms (Diet 3 – S. costatum and Chaetoceros calcitrans; Diet 4 – P. lutheri, S. costatum and C. calcitrans). During conditioning, samples of oysters were collected to evaluate condition index, gonadal development and biochemical composition. At the end of the conditioning period, oysters were induced to spawn to evaluate reproductive output (fecundity, fertilization rate and D‐larvae development). The diets had an impact on the gametogenesis process, energy storage and reproductive output performance, being the best results those obtained in broodstock fed with the diatoms‐predominant diets. However, those fed with diets majority flagellates had an unsuccessful performance. Holistic approaches incorporating all results in this study reveal and reinforce the idea that the diatom species used presented the nutritional requirements to C. angulata broodstock, being essential in the conditioning phase.     

Molecular species diagnosis confirmed the occurrence of Kumamoto oyster <Emphasis Type="Italic">Crassostrea sikamea</Emphasis> in Korean waters

In order to develop an appropriate natural resource management policy, it is important to elucidate the cryptic habitats of species. Oyster species are likely to have such unrecognized habitats owing to the difficulty involved in morphological species identification. In this study, we discovered a novel cryptic habitat of the Kumamoto oyster Crassostrea sikamea, a sibling species of the Pacific oyster C. gigas, in Korean waters. We collected 50 oyster samples from Suncheon Bay, located in the southern Korean Peninsula, among which 20 individuals of C. sikamea, 29 of C. gigas, and one C. sikamea/C. gigas hybrid were identified based on mitochondrial and nuclear DNA markers. There were no significant differences in shell morphology between the two species, which is consistent with how difficult it is to delineate them based on their shell features. Our identification of this novel C. sikamea habitat should help to improve the resource management of East Asian oysters.     

Growth performance and biochemical composition of the oysters Crassostrea sikamea,Crassostrea angulata and their hybrids in southern China

The Kumamoto oyster (Crassostrea sikamea) and the Portuguese oyster (C. angulata) are important aquaculture species which naturally coexist along the southern coast of China. To understand the potential feasibility of hybridization between the two species, we conducted two‐by‐two factorial cross‐experiments in Beihai (Guangxi province), and also compared the survival and growth of the hybrids to that of the two parental progenies during the grow‐out period from July 2014 to July 2015. Genetic analysis confirmed that the hybrid spats were true hybrids. Additionally, the biochemical composition of the 1‐year‐old oyster progenies was determined. In July 2015, the mean shell height of the hybrids was 42.98 ± 6.29 mm, which was higher than that of the Kumamoto oyster progeny. The cumulative survival rate of the hybrids was 26.37 ± 1.32%, which was higher than that of the progeny of the Portuguese oyster. Mean lipid content of the hybrids was 13.65 ± 1.63% of dry weight, which showed obvious heterosis compared to those of the two parental progenies. Observation of gonads revealed that all hybrids were completely fertile. Furthermore, relative expression of the lipid homeostasis genes, SREBP (sterol regulatory element‐binding proteins), PPARα (peroxisome proliferator‐activated receptor) and INSIG (insulin‐induced gene) were found to vary between parental progenies and the hybrids, thus providing a possible reason for difference in the lipid contents of these experimental groups. Overall, the hybrids were viable, rich in lipid and completely fertile and thus could serve as a promising aquaculture stock for oyster breeding in southern China.     

Effect of starvation on biochemical composition and gametogenesis in the Pacific oyster <Emphasis Type="Italic">Crassostrea gigas</Emphasis>

The effects of starvation on biochemical composition and gametogenesis were investigated in the Pacific oyster Crassostrea gigas. Histological analysis, combined with oocyte examination and measurements of protein, glycogen and lipid levels and RNA/DNA ratio from gonad, adductor muscle and mantle tissue of each sex were performed. In the starved groups, C. gigas showed gonad development, but the progress was delayed during the experiment. Glycogen was the first substrate used by C. gigas for dealing with lack of food. While glycogen was rapidly consumed, protein and lipid contents decreased gradually. A decrease in the RNA/DNA ratio in the starved groups in all the body components was found during starvation, illustrating that RNA/DNA ratio was a valid indicator of nutritional condition in C. gigas. A significant increase in water and ash contents and a corresponding decrease in condition index were observed in the starved groups, showing that the water and ash content and condition index were related to the usage of glycogen, lipid and protein reserves in body composition. During starvation, energy reserves were mobilized for survival and gonad development, but spawning was arrested. The information obtained in this study is useful for broodstock management in the Pacific oyster industry.     

Proximate and fatty acid composition of the gonads of wild versus hatchery‐conditioned Pinctada margaritifera broodstock

The composition of protein, carbohydrate, lipid and fatty acids of the gonad of wild female broodstock of black‐lip pearl oyster, Pinctada margaritifera, was compared with oysters fed on a ternary combination of microalgae in hatchery. Artificial feeding was found to be as good as natural feeding in terms of number and size of released eggs. Lipid, protein and carbohydrate reserves of unfed oysters were found to be insufficient to complete oogenesis. The proportions of saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) of the neutral and polar lipids extracted from female gonads were not influenced by variations in the fatty acid composition of the natural food and ternary combination of microalgae in hatchery. T‐Iso, Chaetoceros calcitrans and Chaetoceros muelleri were able to provide sufficient 22:6n‐3 (DHA) and 20:5n‐3 (EPA), two of the most important essential fatty acids required for gametogenesis. The n‐3/n‐6 and 22:5n‐3/20:4n‐3 ratios were consistently higher in the neutral lipids than in the polar lipids. Conversely, the ratio of 20:4n‐3/20:5n‐3, 22:6n‐3/20:5n‐3 and PUFA/SFA was higher in the polar lipids.     

Effects of alternative dietary lipid sources on growth performance,health status and fillet fatty acid composition of hybrid sturgeon (Acipenser baeri Brandt ♀ × Acipenser schrenckii Brandt ♂)

An 8‐week trial was conducted to determine the effects of total replacement of 12.9% fish oil (FO) with soybean oil (SBO), peanut oil (PNO), sunflower seed oil (SFSO), corn oil (CO) and canola oil (CNO) on growth performance, health status and fillet fatty acid composition of hybrid sturgeon (194.28 ± 0.14 g). Compared to the FO group, dietary SBO decreased growth performance (p < .05), increased serum glucose and hepatic lipid content (p < .05). No obvious adverse effects on growth performance and health status were observed in PNO, SFSO and CO groups (p > 0.05). The fish fed with CNO had increased growth performance (p < .05), reduced serum ALT, AST, LDL‐C (p < .05) and enhanced serum GSH‐Px, T‐AOC, and LZM, MPO, C4 (p < .05). The contents of C18:1n9, C18:2n6, and ∑n‐3 PUFA and ∑n‐6 PUFA in fillets showed a positive linear correlation with the diets (p < .05). In summary, PNO, SFSO and CO are probable alternative lipid sources to fully replace FO. Hybrid sturgeon prefers to use CNO as a lipid source with improved growth performance and health status. The fillet fatty acid composition mirrors the dietary fatty acid composition.     

A comparison of the gametogenic cycle between the Pacific oyster Crassostrea gigas and the Suminoe oyster Crassostrea rivularis in Washington State

The gamotogenic cycle of the Suminoe oyster, Crassostrea rivularis, was compared with that of two groups of Pacific oysters (Crassostrea gigas) on an intertidal oyster bed in Oakland Bay, Washington. The Pacific oysters exhibited an earlier and more extensive development of gonad relative to C. rivularis. Resulting carbohydrate depletion was much greater in C. gigas relative to C. rivularis. Both groups of Pacific oysters spawned completely in mid-August. C. rivularis did not spawn but, rather, initiated phagocytosis of gametes by leucocytes. The implications of the results on the development of a marketable “summer” oyster are discussed.     

Folic acid and cyanocobalamin effects on the expression of genes involved in DNA methylation of the oyster Crassostrea gigas

The microalga Chaetoceros calcitrans was cultured with three concentrations of vitamin B12 (cyanocobalamin) to supplement the feed for the oyster Crassostrea gigas. In two additional assays, vitamins B12 and B9 (folic acid) were dissolved in the water to increase the methyl donors necessary for the one‐carbon cycle and DNA methylation. Microalgae did not present differences in their concentration of vitamins, and no correlation was found between the concentration of vitamin supplement and the vitamin concentration in oysters; however, changes in the expression of genes involved in the DNA methylation were found. The expression of proton‐coupled folate transporter (PCFT) was lower in oysters supplemented with Vit. B9. The expression of proton‐coupled folate transporter (PCFT) was lower in oysters supplemented with Vit. B9., however, the expression of genes implicated in the release of the methyl used to maintain methylation such as methionine synthase (MS) and DNMT1 expression was high, suggesting faster transportation of Vit. B9. The methylenetetrahydrofolate reductase (MTHFR), implicated in the reduction of folic acid, was lower in oysters supplemented with Vit. 9 and B12 dissolved in the water. DNA methyltransferase DNMT1A, involved in DNA maintenance, was higher in oyster supplemented with Vit. B9, but the expression of DNMT1B was not different. In conclusion, the supplementation with folic acid increases the expression of genes implicated in the maintenance of DNA methylation in C. gigas.     

Comparative analysis of Vibrio splendidus-related strains isolated during Crassostrea gigas mortality events

French mollusc production is based mainly on the Pacific cupped oyster, Crassostrea gigas. Since 1991, annual mass mortality of juveniles has been reported during summer months. These recurring episodes concern professionals who fear that like Portugese oyster, C. angulata, C. gigas could in turn disappear following one of these epizooties. Previously, bacteriological analysis of moribund oyster juveniles yielded an isolate of a Vibrio splendidus biovar II strain, named TNEMF6. This isolate was demonstrated to be pathogenic to Crassostrea gigas spat by experimental challenge. To study the association between summer oyster mortality and presence of TNEMF6 cluster strains, Vibrionaceae fauna were isolated from infected spat along the French Atlantic coast between 1997-1998. Strains related to V. splendidus biovar II were selected. Comparison with TNEMF6 was performed by classical biochemical tests and polymerase chain reaction – restriction fragment length polymorphism (PCR-RFLP) of SSU rDNA, rpoD, and gyrB genes. Genomic similarities were confirmed by DNA/DNA hybridization. Only one strain out of 14, TNNIII7, was found to be closely related to the pathogenic bacteria. Neither the phenotypic nor the genotypic markers used in this study were able to distinguish pathogenic from non-pathogenic strains of the widespread V. splendidus. However, future genetic comparisons of TNEMF6 and TNNIII7 is likely to reveal genes involved in pathogenicity.     

Comparative study on nutrient composition and quality evaluation in a new variety and wild‐typed ridgetail white prawn (Exopalaemon carinicauda)

Kesuhong No. 1 with high concentration of astaxanthin was a newly approved aquaculture variety of ridgetail white prawn (Exopalaemon carinicauda) in China, and the information on the nutrient composition and quality evaluation of this new variety is insufficient. Thus, the proximate composition, amino acid and fatty acid profiles were analysed and compared between the new variety and the wild‐typed prawn in the present study, for its better application of the new variety. It showed that there were no significant differences (p > 0.05) of the proximate composition, essential amino acid and saturated fatty acid (SFA) of muscle tissue between the wild‐typed prawn and the new variety. However, for the content of some delicious amino acids (Ala and Tyr), it was significantly higher (p < 0.05) than that in the wild‐typed prawn. Similarly, for some ω3 polyunsaturated fatty acids (ω3 PUFA), such as docosahexaenoic acid (DHA) and eicosapntemacnioc acid (EPA), it was also significantly higher (p < 0.05) than that in the wild‐typed prawn. In addition, higher PUFA/SFA ratio and lower ω6/ω3 ratio also improved muscle quality in the new variety. Information obtained in the present study indicates a promising natural source of ω3 PUFA with high nutritional value, and has strong potential application value in this new variety of E. carinicauda.     

Suspended culture evaluation of Pacific oyster Crassostrea gigas in a tropical estuary

The growth and survival of Crassostrea gigas were evaluated in hanging culture in the Chone River estuary (Bahía de Caráquez), Manabí province, Ecuador. Oyster seeds (~10 mm) were confined in lantern nets at a density equal to the occupation of half the surface of the basket base, until reaching commercial size (80 mm). A sample for oyster biometric, parasitic and bacterial analysis was obtained monthly. Temperature, salinity, oxygen concentration, seston and phytoplankton biomass were determined. At the end of the study, the oysters were analysed for heavy metal concentration. The commercial oyster production was extrapolated to estimate the possible economic performance of a family production module (a 7 × 7 m bamboo raft). The results show a great biological feasibility of culture of C. gigas with harvests of commercial size oysters in only 5 months and acceptable survivals (accumulated >70%, after 3 weeks of crop seed selection). The heavy metal concentrations and the parasitological and bacteriological analyses did not indicate levels of contamination. The economic projections suggest that, even with a profitability of 57%, the initially invested capital could be recovered within the first harvest.     

三种水族馆珍贵鱼类的营养成分分析及脂肪酸营养评价

睛斑鳗狼鱼、巨巴西骨舌鱼和锥齿鲨是水族馆中珍贵的展示鱼类,但是有关这3种鱼类成体的营养生理研究却十分缺乏。本研究对从水族馆获得的成年睛斑鳗狼鱼、巨巴西骨舌鱼和锥齿鲨的肌肉和肝脏组织进行了常规营养成分(水分、灰分、粗蛋白和粗脂肪含量)和脂肪酸组成测定分析,并进一步将3种鱼类所食饵料与其肝脏和肌肉中的脂肪酸相对含量进行了比较。结果显示,在3种鱼中,锥齿鲨肌肉和肝脏中的蛋白质含量最高,分别为26.84%和24.03%;睛斑鳗狼鱼的肌肉和肝脏中的脂肪含量最高,分别为41.96%和32.27%;巨巴西骨舌鱼的肌肉和肝脏中的灰分含量最高,分别为4.95%和5.51%。锥齿鲨肌肉和肝脏中饱和脂肪酸(SFA)含量高于睛斑鳗狼鱼,睛斑鳗狼鱼肌肉和肝脏中单不饱和脂肪酸(MUFA)含量高于巨巴西骨舌鱼和锥齿鲨,巨巴西骨舌鱼肌肉和肝脏中多不饱和脂肪酸(PUFA)含量及其肌肉中UFA/SFA值高于睛斑鳗狼鱼和锥齿鲨。研究表明,锥齿鲨所食饵料与其体内脂肪酸组成最为相似,其肌肉和肝脏与饵料的相关系数分别为0.972和0.861,其次是巨巴西骨舌鱼(0.912和0.846),而睛斑鳗狼鱼肌肉和肝脏中脂肪酸组成与所食饵料的相关系数仅分别为0.760和0.681。从脂肪酸营养的角度分析,在当前水族馆养殖条件下,锥齿鲨饵料较为合适,巨巴西骨舌鱼的饵料中应注意添加EPA和DHA,而睛斑鳗狼鱼饵料中则需提高MUFA比例。本研究首次阐明了3种珍贵的水族馆鱼类成体的营养组成,并为水族馆相应的饲料配制提供了重要的参考依据。     

Two epizootic Perkinsus spp. events in commercial oyster farms at Santa Catarina,Brazil

Perkinsus spp. have been detected in various bivalve species from north‐east Brazil. Santa Catarina is a South Brasil state with the highest national oyster production. Considering the pathogenicity of some Perkinsus spp., a study was carried out to survey perkinsosis in two oyster species cultured in this State, the mangrove oyster Crassostrea gasar and the Pacific oyster Crassostrea gigas. Sampling involved eight sites along the state coast, and oyster sampling was collected during the period between January 2013 and December 2014. For the detection of Perkinsus, Ray's fluid thioglycollate medium (RFTM) and histology were used, and for the identification of the species, PCR and DNA sequencing were used. Perkinsus spp. was found by RFTM in C. gigas and C. gasar from São Francisco do Sul. This pathology was also detected in C. gasar from Balneário Barra do Sul both, by RFTM and histology. Perkinsus marinus was identified in C. gigas and C. gasar from São Francisco do Sul and Perkinsus beihaiensis in C. gasar from Balneário Barra do Sul. This is the first report of P. marinus in C. gigas from South America. Results of this preliminary study suggest that both oyster species tolerate the species of Perkinsus identified, without suffering heavy lesions.     

In search of the Kumamoto oyster <Emphasis Type="Italic">Crassostrea sikamea</Emphasis> (Amemiya, 1928) based on molecular markers: is the natural resource at stake?

A cornerstone in conserving wildlife is to resolve taxonomic uncertainties over organisms so that conservationists can define the entity that should be conserved. This is the case for two closely related Crassostrea oysters inhabiting the Ariake Sea (Kyushu, Japan) in sympatry, the kumamoto oyster C. sikamea and Pacific oyster C. gigas, where molecular markers have shed light on their taxonomic separation and species diagnosis. In the past, there was a concern that Kumamoto oysters may be at risk of extinction. However, several field surveys equipped with species-diagnosis molecular markers have provided solid evidence that this perception is incorrect. Nevertheless, previous studies have sometimes given conflicting results, throwing us into confusion about the resource status. Research on natural Kumamoto oysters that the author hopes could help to enhance our understanding of the conservation of this invaluable oyster is reviewed here.