Oyster Culture Research Articles

Marker-assisted selection in a Pacific oyster population for an antiviral QTL conferring increased survival to OsHV-1 mortality events in Tomales Bay

Aquaculture of Pacific oysters (Crassostrea gigas) around the world is stymied by mortality events triggered by Ostreid herpesvirus 1 (OsHV-1). In Tomales Bay, California, where OsHV-1 is endemic, breeding through family-based pedigree selection has achieved considerable genetic gains in survival to mortality events. In this study, a genome-wide association study with unselected and selected oyster families was performed that led to the detection of one quantitative trait locus (QTL) on chromosome 8 of the Pacific oyster genome that was associated with survival to mortality events in Tomales Bay and explained 13% of the phenotypic variance. RT-qPCR was used to determine that the basal upregulation of two antiviral genes, IRF2 and Viperin, was also associated with this QTL. Marker-assisted selection for this QTL was performed and families selected in this manner had 47% greater survival breeding values than families selected using pedigree selection alone. Future fine-mapping of this QTL could potentially provide a mechanistic understanding of OsHV-1 tolerance in Tomales Bay.

Artificial weathering of plastics used in oyster farming

With the omnipresence of plastic litter from oyster farming in marine coastal areas, the objective of this work was to better understand the weathering of plastics used in this field, focusing on oyster spat collectors. During their use, around fifteen years, collectors made of polypropylene (PP) undergo numerous degradations, alternatively submerged, emerged in seawater, and stored outdoor until the next cycle. They weaken, crack, break, end up fragmenting and disseminated in the environment as microplastics associated to persistent organic pollutants. In this work, a comparison of 55 months of in situ weathering with five months of artificial weathering in air or in artificial seawater in a homemade UV chamber was conducted to better understand the mechanisms involved. Chemical, thermal and surface characterizations of virgin and weathered samples were conducted using Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and Environmental Scanning Electron Microscopy (ESEM). After 55 months of in situ weathering, collectors were notably damaged with large fissures and loss of microplastics (MPs) associated with an increase of carbonyl index values and a decrease of melting temperatures and crystallinity rates. Considering only UV irradiation, five months of artificial weathering at 30 °C under continuous irradiation of 6.9 W/m2 under UV lamps (295–400 nm) reproduced approximately 4.4 months of natural sunlight. Artificial weathering confirmed that photooxidation by combined effects of UV rays and oxygen was the main weathering mechanism and was reduced in seawater. These results help to understand the mechanisms involved in the weathering of these collectors in the marine environment and provide valuable information for industrials and professionals. Our study suggests a better storage away from UV rays and a reduction of the duration of use compared to current practices.

Development and Evaluation of High-Density SNP Arrays for the Eastern Oyster Crassostrea virginica.

The eastern oyster Crassostrea virginica is a major aquaculture species for the USA. The sustainable development of eastern oyster aquaculture depends upon the continued improvement of cultured stocks through advanced breeding technologies. The Eastern Oyster Breeding Consortium (EOBC) was formed to advance the genetics and breeding of the eastern oyster. To facilitate efficient genotyping needed for genomic studies and selection, the consortium developed two single-nucleotide polymorphism (SNP) arrays for the eastern oyster: one screening array with 566K SNPs and one breeders' array with 66K SNPs. The 566K screening array was developed based on whole-genome resequencing data from 292 oysters from Atlantic and Gulf of Mexico populations; it contains 566,262 SNPs including 47K from protein-coding genes with a marker conversion rate of 48.34%. The 66K array was developed using best-performing SNPs from the screening array, which contained 65,893 oyster SNPs including 22,984 genic markers with a calling rate of 99.34%, a concordance rate of 99.81%, and a much-improved marker conversion rate of 92.04%. Null alleles attributable to large indels were found in 13.1% of the SNPs, suggesting that copy number variation is pervasive. Both arrays provided easy identification and separation of selected stocks from wild progenitor populations. The arrays contain 31 mitochondrial SNPs that allowed unambiguous identification of Gulf mitochondrial genotypes in some Atlantic populations. The arrays also contain 756 probes from 13 oyster and human pathogens for possible detection. Our results show that marker conversion rate is low in high polymorphism species and that the two-step process of array development can greatly improve array performance. The two arrays will advance genomic research and accelerate genetic improvement of the eastern oyster by delineating genetic architecture of production traits and enabling genomic selection. The arrays also may be used to monitor pedigree and inbreeding, identify selected stocks and their introgression into wild populations, and assess the success of oyster restoration.

Oregon shellfish farmers: Perceptions of stressors, adaptive strategies, and policy linkages

In the United States, domestic oyster aquaculture production is insufficient to meet national demand, thus creating a reliance on international oyster imports for consumption. West coast shellfish farmers are threatened by climate change, including ocean acidification as well as socioeconomic challenges such as labor availability. To expand and enhance United States oyster production, and support domestic food security and livelihoods, a better understanding of the limitations that oyster farmers’ experience, and corresponding pathways forward for adaptation is needed. Through semi-structured interviews conducted with commercial Oregon shellfish farmers, we assess the environmental, economic, social and regulatory stressors impacting oyster growing operations, and the corresponding adaptive strategies employed or envisioned by aquaculture farmers. We find farmers are most impacted by environmental stressors (nuisance species that interact with oysters or oyster habitat negatively), followed by regulatory and economic stressors (permitting and regulations and labor availability). Farmers perceived ocean acidification as a risk, but primarily at the oyster larva stage rather than the juvenile or adult grow-out stage. Examples of farmer-identified adaptive strategies included streamlining permitting and regulations, incentivizing employee retention, and having flexibility in culture type to avoid nuisance species and other environmental stressors. An increase in targeted outreach related to aquaculture policies and engagement with industry, scientists, managers, and policy-makers could facilitate policies that support these and other adaptive strategies.

Socioeconomic adaptation to geomorphological change: An empirical study in Cigu Lagoon, southwestern coast of Taiwan

Coastal erosion in the lagoon systems is concerned as they are dynamic landscapes, often highly productive and beneficial to humankind. Cigu Lagoon contains rich and diverse ecosystems ranging from mangroves to salt fields, and from fish to birds (e.g., endangered black-faced spoonbill). As well as forming part of the country’s natural defenses against typhoons and storm surges, it is also economically important for oyster farming, fish-pond aquaculture and ecotourism. However, with the construction of reservoir, fishery harbors and breakwaters, sediment transport decreases and sand barrier islands have eroded, narrowed, lowered and moved landwards. Cigu is a rural area with decreasing, aging population, becoming a “super-aged society” as defined by World Health Organization. Therefore, it is imperative to study the socioeconomic impacts of these changes, and then to explore critical adaptation factors and potential adaptation strategies. In this research, we conducted interviews and a fuzzy analytic hierarchy process survey. Diverse stakeholders were identified and mapped using a stakeholder rainbow diagram and a power–interest grid. The results show that stakeholders consider the economy to be the most important adaptation factor, especially in relation to the employment opportunities. There are some forms of livelihood diversification in Cigu. Collaboration among young entrepreneurs is the key to socioeconomic adaptation. These factors and strategies may foster socioeconomic adaptation to coastal erosion or geomorphological change, to be aggravated by climate change and other stressors.

Nekton use of co-occurring aquaculture and seagrass structure on tidal flats

On the extensive tidal flats of Willapa Bay (Pacific coast, USA), oyster culture, seagrass, and mudflats create a mosaic of intertidal habitats. Structured habitats are generally considered to increase abundance and diversity of associated species, but less attention has been paid to roles of different kinds of structure (seagrass meadows, reefs, farm infrastructure) or co-occurring structure in shaping nekton assemblage structure. Here, we investigated the effects of different oyster culture methods (suspended culture and bottom culture) on nekton communities and abundance across a gradient of seagrass habitats, during multiple seasons, and using both seine and video sampling methods. Of 23 major estuarine taxa, 2 were generally associated with vertical structure (eelgrass or suspended culture), 3 were seagrass specialists, and 3 primarily used habitats lacking vertical structure (mudflats and bottom culture). Where oyster culture was present, 5 taxa associated with on-bottom and 2 taxa associated with suspended culture. Assemblage structure responded to co-occurring structure as expected from responses to each structure type independently (i.e. additive effects of seagrass and oyster culture). In contrast to much empirical evidence in structured habitats, seagrass density was a poor predictor of overall fish abundance. These findings together suggest that maintaining a mosaic of available habitats is favorable for promoting diversity in Willapa Bay.

The Effect of Starvation on the Antioxidant Complex of the Bivalve Mollusk <i>Anadara kagoshimensis</i> (Tokunaga, 1906) from the Black Sea

The effect of 30-day starvation on the state of the antioxidant complex and lipid peroxidation in the tissues of the Black Sea bivalve mollusks Anadara kagoshimensis (Tokunaga, 1906) was studied. Mollusks were collec-ted on a mussel and oyster farm near the village Katsiveli (the Southern coast of Crimea, the Black Sea) on April 2020. The mollusks were kept in aquariums with a closed water exchange system with biofiltration of water. The mollusks of the experimental group were not fed for 30 days. The activity of glutathione peroxidase, glutathione reductase, superoxide dismutase, catalase, the content of reduced glutathione and TBA-reactive products were determined. It was found that under fasting conditions the content of TBA-reactive products decreased in the hepatopancreas and the foot of the mollusk, and did not change in the gills. The most pronounced changes in the AO complex – an increase in all the studied parameters – were detected in the hepatopancreas. An increase only in the parameters of the antioxidant glutathione system was found in the foot, and an increase only in the activity of glutathione peroxidase and in the content of reduced glutathione was found in the gills. The results obtained in the study have shown a stable antioxidant-prooxidant ba-lance in the bivalve mollusk A. kagoshimensis under starvation conditions.

THE EFFECT OF THE SOAKING PERIOD IN NATURAL FEED TATTS of Chaetoceros sp. ON THE GROWTH AND VIABILITY OF PEARL CLASS (Pinctada maxima) SEEDS

Pearl oysters are a marine aquaculture commodity with high economic value. However, there are still many obstacles in pearl oyster cultivation activities, such as the need for quality seeds. This study aims to determine the effect of immersing pearl seeds in natural feed tanks of Chaetocheros sp. with different immersion periods on the growth and survival rate of pearl oyster (Pinctada maxima) seeds. The method used in this study is an experimental method using a completely randomized design (CRD), with 5 treatments and 3 replications, namely A (control/without immersion), B (0.5 hours), C (1 hour), D (1, 5 Hours) and E (2 Hours). The results showed that soaking the seeds in natural feed tanks had a significant effect on the growth of the shell (dorsal-ventral) of the pearl oyster Pinctada maxima (p<0.05). The highest growth was achieved in the 2-hour immersion period with an absolute growth value of 1.67 mm, a relative growth of 68.49% from the initial size, and a daily specific growth rate of 3.31% per day. This method must be tested on larger pearl oyster seeds and using other natural feed species and various natural mixes (multi-species).

Effect of waste oyster shell powder on the properties of alkali-activated slag–waste ceramic geopolymers

The ceramic and oyster farming industries produce large amounts of waste ceramics and oyster shells. Meanwhile, alkali-activated materials are less environmentally impacted materials with the potential to replace Portland cement. Adding ceramic powder (CP) and waste oyster shell powder (WOS) to alkali-activated materials can relieve the pressure on landfills and protect the environment, thereby having important implications. This study aims to add WOS to alkali-activated adhesives and investigate their effects on the properties of the samples. The blast furnace slag and ceramic powder were partially replaced by 0–20 wt% WOS. The specimens for control, 10% WOS, and 20% WOS are named as WOS-0, WOS-10, and WOS-20, respectively. Experimental studies on the compressive strength testing, heat of hydration, ultrasonic pulse velocity (UPV), thermogravimetric (TG) analysis, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and electrical resistance rate were performed. The experimental results are as follows: (1) An increase in the WOS substitution rate increased the hydration heat release rate and decreased the compressive strength. At 3 days of age, the compressive strength of the WOS-20 sample decreased by 4.3 MPa compared with the WOS-0 sample. (2) UPV and resistivity decreased with increasing WOS substitution. At 3 days of age, the UPV of the WOS-20 sample decreased by 0.11 km/s compared with the WOS-0 sample. (3) The TG results showed that WOS participated in the alkali-activated reaction. For the WOS-20 sample, the amount of calcium carbonate decreased by 2.9% as the age increased from 3 days to 28 days. (4) XRD and FT-IR spectra showed the intensified carbonate peak with the increase in the WOS content. These findings suggest that CP and WOS can be used as complementary gelling agents for alkali-activated materials.

Don't go breaking apart: Anthropogenic disturbances predict meadow fragmentation of an endangered seagrass

Abstract Although it is well established that human activities are linked to the loss of seagrasses worldwide, the influence of anthropogenic disturbances on the habitat fragmentation of seagrass meadows is less understood. This information is essential to identify how humans are modifying seascapes and what disturbances pose the greatest risk to seagrasses, which is pertinent given the rapid urbanization occurring in coastal areas. This study examined how the habitat fragmentation of an endangered seagrass Posidonia australis varied in relation to several anthropogenic disturbances (i.e. human population, marine infrastructure, terrestrial run‐off and catchment land‐usage) within 10 estuaries across 620 km of coastline in New South Wales, Australia. When comparing between estuaries, the fragmentation of P. australis meadows was significantly greater in estuaries adjacent to highly populated metropolitan centres – generally in the Greater Sydney region. At sites within estuaries, the density of boat moorings was the most important predictor of habitat fragmentation, but there was also evidence of higher fragmentation with increased numbers of jetties and oyster aquaculture leases. These results suggest that the fragmentation of seagrass meadows will become more pervasive as the human population continues to grow and estuarine development increases. Strategies to mitigate anthropogenic disturbances on seagrass meadow fragmentation could include prohibiting the construction of boat moorings and other artificial structures in areas where seagrasses are present or promoting environmentally friendly designs for marine infrastructure. This knowledge will support ongoing management actions attempting to balance coastal development and the conservation of seagrasses.

Pollution sources and ecological risks of potentially toxic metals in sediments from a multi-functional Hsingda Harbor in southwestern Taiwan

Sediment metal pollution was assessed in a multi-functional harbor in southwestern Taiwan, Hsingda Harbor, which was developed from a traditional fishing port. Contamination level and ecological risks were identified using multiple sediment pollution indices referenced from the total metal contents (Cu, Zn, Pb, Cr, Ni, Hg, and Ag) and their chemical partitioning factions. This study used local background, normalization with Fe content, and correlation with total organic carbon to differentiate between natural and anthropogenic sources. Results showed that fisheries-related activities and the nearby coal-fired power plant primarily contributed to potentially toxic metal pollution. Remarkably, Cu, Zn, Pb, Cr, and Hg contents in the sediments along the nearshore fishing port (77.7, 270, 50.4, 99.1, and 0.31 mg/kg) were up to 2.1–9.5 times higher the background site. Significant Cu and Pb enrichment (EF: 5.4–6.6) may be attributed to antifouling paints and coal ashes. The adjacent oyster farm sediments were enriched with Cu and Zn (EF: 2.5–4.5), potentially threatening the oyster quality and public health. Moderate–high and low ecological risks were obtained from the assessments of total metal contents (PERI: 116–340) and extractable fractions (GRI: 9.0–28.6), respectively. Using total metals and chemical partitioning data provides a better understanding of potential ecological risks in sediments. Our results provide valuable information for environmental pollution control and mitigation during harbor development and management.

Using the roughness height and manning number in hydrodynamic model to estimate the impact of intensive oyster aquaculture by floating & fixed rafts on water exchange with an application in Qinzhou Bay, China

This study mainly addressed the methodology issue of how to model the hydrodynamic drag effects of aquaculture facilities and activities. Here, firstly, surface shear stress was determined by roughness height for characterizing the drag from floating aquaculture activities, while bottom shear stress was determined by the Manning number for characterizing the drag caused by bottom fixed aquaculture activities. Then, by taking Qinzhou Bay as a typical case, the two-dimensional model was established by integrating the multiple drag coefficients to quantify the impacts of the oyster cultivation activities on the water exchange capability (tidal prism and half-life time). The results showed that: (1) Cultivation activities would reduce the average tidal prism by 6.4% in Qinzhou Bay; (2) 10 averages longer day of half-life time was estimated to be resulting from the cultivation drag.

New records of invasive tubeworms (Ficopomatus, Serpulidae) in Mexico

AbstractFicopomatus Southern, 1921 is a serpulid genus currently composed of six species, two of which (F. enigmaticus and F. miamiensis) are reef-builders. The former has invaded subtropical and warm-temperate estuaries worldwide, causing environmental and economic harm. In this study, Ficopomatus miamiensis and F. uschakovi are reported from brackish-water coastal localities in both Atlantic and Pacific sides of Mexico, including a Biosphere Reserve, estuaries, as well as shrimp and oyster farms. Ficopomatus miamiensis is reported from Veracruz (southern Gulf of Mexico, Mexico territory) and Sinaloa (southern Gulf of California). Ficopomatus uschakovi is reported for the first time in the southern Gulf of Mexico (Mexico territory) and repeatedly recorded in Chiapas (southern Mexican Pacific). There are no phenotypic differences between specimens of F. miamiensis from both coasts of Mexico. Comparison of mitochondrial cytochrome b (Cytb) DNA sequences further support the notion that F. miamiensis from the type locality (Florida) and Atlantic coasts of Mexico is also found along the Pacific coast of Mexico. Morphological variability within specimens of F. uschakovi from a single locality (either Laguna del Ostión or La Encrucijada) in Mexico suggest potential presence of multiple cryptic species. Molecular genetics studies are needed to confirm the taxonomic and invasive status of F. uschakovi.

Meteorological and Water Quality Factors Associated with Microbial Diversity in Coastal Water from Intensified Oyster Production Areas of Thailand

Coastal pollution is of public health concern due to the possibility of bacterial contamination in aquaculture affecting health risk and seafood safety. This study determined the concentrations of total coliforms, fecal coliforms, E. coli, and V. parahaemolyticus and the presence of V. cholerae and Salmonella in water and measured water quality and meteorological factors from the major oyster cultivation areas in Thailand. The water samples (n = 363) were collected from Surat Thani (n = 60), Chanthaburi (n = 60), Trat (n = 60), Phetchaburi (n = 60), Chonburi (n = 63), and Phang Nga (n = 60) from February 2021 to January 2022. The prevalence of total coliforms (96.7%), fecal coliforms (60.6%), E. coli (22.9%), along with the prevalence of Salmonella (2.5%), Vibrio parahaemolyticus (74.9%), and V. cholerae (11.3%) were determined. Common Salmonella serovars were Othmarschen and Lamberhurst. The concentration of E. coli was significantly associated with dissolved oxygen and precipitation (p < 0.0001). Therefore, continuing microbiological monitoring and surveillance of water for coastal aquaculture is important to produce safe aquatic products. Furthermore, raising awareness of coastal pollution and seafood safety will help enhance sustainable coastal fisheries in Thailand.

Role of the Vibrio community, reproductive effort, and environmental parameters in intertidal Pacific oyster summer mortality in British Columbia, Canada

In recent years, mortality of cultured Pacific oysters (Crassostrea gigas) during July and August has regularly exceeded 50% in many oyster farms in Baynes Sound, British Columbia (BC), Canada. However, little is known about the bacterial diversity and environmental/biological conditions that may be contributing to such mortality events in the region. A study of Pacific oysters in intertidal culture trays was conducted during the summer of 2017 in Baynes Sound to monitor the occurrence of oyster mortality, while identifying potentially pathogenic bacteria present in the oysters, examining oyster reproductive development, and recording various environmental parameters (temperature, salinity, dissolved oxygen, chlorophyll a, carbon chemistry, phytoplankton species/abundance, zooplankton species/abundance) at three farm sites in Buckley Bay, Fanny Bay, and Ship's Point. Continuous mortality was observed throughout July and August, cumulative mortalities ranging from 16.5 to 35.1% at the three sites. Mortality over time was examined with a binomial generalized linear mixed-effects regression model, which demonstrated a correlation with date, tides, temperature, gonad somatic index, and gonad developmental phase (Rc2 = 0.598). Average cumulative mortality per module was highly correlated with average oyster gonad length and the proportion of female oysters in a multiple linear-regression model (p = 0.002, R2 = 0.824). A total of 158 bacterial isolates were cultured and identified based on sequencing of the recA gene. Among those isolates, Vibrio aestuarianus and V. harveyi, with 27 and three isolates, respectively, are well-documented pathogens of Pacific oysters in other regions. This study is the first to concurrently evaluate a broad array of factors potentially associated with Pacific oyster summer mortality in BC. We provide evidence that summer mortality of Pacific oysters in Baynes Sound is occurring with an etiology similar to summer mortalities of adult Pacific oysters reported in other countries.

Molecular Epidemiology of Antimicrobial Resistance and Virulence Profiles of Escherichia coli, Salmonella spp., and Vibrio spp. Isolated from Coastal Seawater for Aquaculture.

The occurrence of waterborne antimicrobial-resistant (AMR) bacteria in areas of high-density oyster cultivation is an ongoing environmental and public health threat given the popularity of shellfish consumption, water-related human recreation throughout coastal Thailand, and the geographical expansion of Thailand's shellfish industry. This study characterized the association of phenotypic and genotypic AMR, including extended-spectrum β-lactamase (ESBL) production, and virulence genes isolated from waterborne Escherichia coli (E. coli) (n = 84), Salmonella enterica (S. enterica) subsp. enterica (n = 12), Vibrio parahaemolyticus (V. parahaemolyticus) (n = 249), and Vibrio cholerae (V. cholerae) (n = 39) from Thailand's coastal aquaculture regions. All Salmonella (100.0%) and half of V. cholerae (51.3%) isolates harbored their unique virulence gene, invA and ompW, respectively. The majority of isolates of V. parahaemolyticus and E. coli, ~25% of S. enterica subsp. enterica, and ~12% of V. cholerae, exhibited phenotypic AMR to multiple antimicrobials, with 8.9% of all coastal water isolates exhibiting multidrug resistance (MDR). Taken together, we recommend that coastal water quality surveillance programs include monitoring for bacterial AMR for food safety and recreational water exposure to water for Thailand's coastal water resources.

Secure Wireless Sensor Network using Cryptography for Smart Farming Systems

Internet of Things (IoT) technology has become part of human life. Agriculture in many parts is one of IoT implementation segment including the Cultivation of mold oysters. Internet of Things (IoT) is applied to collect data from combined sensors in the Wireless Sensor Network (WSN) will make it easy for farmers to monitor and control garden they remotely. Regardless of the application system control distance far based WSN that will make it easy for a farmer, the system has gap security, and one of them that is hacking and tapping of communication data The IoT . is really dangerous on effort if condition room mold oyster the known by someone hacker who can just is rival effort. It is a needed something method for secure communication when the data transfer process is over-guaranteed. The method used is application Base64 -based data encryption/decryption on WSN node devices and controlling and monitoring mobile devices. Based on results trials carried out after the implementation of Secure WSN with scenario tapping using the Wireshark tool show no data can be read. Analysis results show that this model could be applied as Secure WSN for Smart Farming System.

Oyster Mussels (Crassostrea gigas) Transport System (Case Study in Kamashima Company) in Hyogo, Japan

Oyster culture is an aquaculture activity that is mostly carried out in Japanese waters. While in Indonesia, oyster shells are widely consumed, but they have not been produced through the culture process but are caught on the high seas. This study aims to determine how the application of technology and transportation in the culture and sale of oyster in Japan. Based on literature studies and activities at the Kamashima-Japan company, transportation is an important part of oyster farming activities. Oyster transportation technology is currently carried out in two areas, namely sea and land, using open and closed dry transportation methods. Sea transportation uses Hydraulic Cranes for Shipboard Use (Marine Cranes) technology which is applied to special vessels measuring 6-7 GT with the classification of Truck-mounted cranes, while land transportation uses Styrofoam boxes equipped with ice blocks to immobilize the temperature. The size of the wind that blows in the sea, the time of pick-up and delivery, and the number of oyster shells required are important factors in these transportation activities.

Studies of interspecific backcross between hybrids of (Crassostrea angulata ♀ × C. gigas ♂) and their two parental species

Interspecific hybridization between oysters Crassostrea angulata and C. gigas has been recently studied, but it remains unclear how these hybrids can be used to advance the techniques of oyster farming. Interspecific backcrossing is expected to transfer the favorable traits of a species to genetically altered F1 hybrids. In this study, therefore, interspecific backcrosses were conducted between the hybrids of C. angulata ♀ × C. gigas ♂ and their parental species, which included nine groups based on their crossed combinations: hybrid combinations and self-breeding (AG GA, GG and AA); backcross combinations (HA, HG, AH and GH); hybrid self-breeding (HH). Results showed high cleavage rate and D-larval rate in each group without fertilization barrier. Among groups, we observed (1) the highest shell height of AG on Day 12, (2) faster growth of AH than other groups from Day 90 to Day 180, (3) the highest shell height of AG after Day 180. Limited superiority of the backcross groups was found on Day 360, but the degree of heterosis of AG and AH was higher than that of other groups. A mild degree of outbreeding depression in terms of growth was found in self-breeding progenies. The survival rate among groups follows an order: the group with C. angulata as Dam > the group with the hybrid as Dam > the group with C. gigas as Dam. Positive outbreeding depression in terms of survival rate was observed on Day 360. In particular, the survival rate of AH was higher than that of other groups with a heterosis value of 54.80% at the harvest stage. In terms of relative yield, outbreeding depression and inconspicuous superiority were found. Overall, hybrid combination AG exhibited the best performance among groups, followed by backcross combination AH.

BUSINESS PROSPECTS FOR CULTIVATION OF OYSTER (Crassostrea gi-gas) IN OKAYAMA, JAPAN

Japan is known as one of pioneering countries in oyster cultivation. This study aims to reveal the prospects for the cultivation of pacific oysters. The analysis of investment evaluation criteria in this study is based on financial analysis methods which include Benefit-Cost Ratio (BCR), Break Even Point (BEP), Return of Investment ROI, and Payback Period. The process carried out in the oyster cultivation steps starts from spawning and oyster fry, growth control (Yokusei), hanging (Hansuika) and seeding (Tanetsuke), check growth and landing and marketing. Based on the results of data analysis, it is obtained that the values of BCR, BEP, ROI, and Payback Period respectively are 1.88, 1,155.5 kg, 47%/year, 25.6 months. In this analysis, it is obtained that the BCR value is more than 1, so the business prospects for the oyster cultivation are very feasible to do. The benefit of this study is that the description of prospects and the financial analysis presented can be a consideration and reference for people who have an interest in oyster farming, especially for small-scale businesses.