Mangrove Oyster Crassostrea Gasar Research Articles

Assessment of genetic resources of the mangrove oyster Crassostrea gasar along the south and southeast coast of Brazil: baseline for its conservation and sustainable use

Assessment of genetic resources of the mangrove oyster Crassostrea gasar along the south and southeast coast of Brazil: baseline for its conservation and sustainable use

Genetic Structure and Diversity in Wild and Cultivated Populations of the Mangrove Oyster Crassostrea gasar from Southern Brazil.

The mangrove oyster (Crassostrea gasar) is Brazil's second most cultured species and presents a high potential for aquaculture. However, artificial selection in a highly fecund species and significant variance in reproductive success can result in the loss of genetic diversity and increases the inbreedingrate, especially in cultivated populations. In this study, we investigated the genetic structure and diversity of C. gasar in wild and cultivated populations using 14 microsatellites. Spatial genetic comparisons revealed the existence of two main genetic groups of C. gasar, one comprising the population in cultivation and the other formed by wild populations along the southern and southeastern Braziliancoasts. Although no common genetic structure exists among wild populations, it is possible to observe a distribution gradient based on discriminant analysis of principal components consistent with their geographic distribution. However, it is insufficient to differentiate them genetically. Despite artificial reproduction, thegenetic diversity values of the cultivated population remained relatively high and did not show areduction. Therefore, monitoring the cultivated population and establishing reference values for genetic diversity will allow the adoption of strategies both for the viability of the cultivated population and the management of wild populations.

Effects of cadmium and zinc on gene expression of novel molecular biomarkers in the mangrove oyster Crassostrea gasar

Metal contamination impacts various aquatic species, and mollusk bivalves are appropriate sentinel organisms in coastal pollution assessment. Metal exposure can disrupt homeostasis, alter gene expression, and harm cellular processes. However, organisms have evolved mechanisms to regulate metal ions and counteract their toxicity. This study examined the effect of acute cadmium (Cd) and zinc (Zn) on metal-related gene expression in gills of Crassostrea gasar following 24 and 48 h of laboratory exposure. We focused on Zn transport, metallothionein (MT), glutathione (GSH) biosynthesis, and calcium (Ca) transporter genes to understand the underlying Cd and Zn-accumulating mechanisms that prevent metal toxicity. Our findings revealed increased Cd and Zn levels in oyster gills, with significantly higher accumulation after 48 h. C. gasar accumulated high Cd concentrations even in scarce conditions and increased Zn levels, suggesting a strategy to cope with toxicity. While no significant gene expression differences were observed after 24 h, the increased metal accumulation after 48 h led to upregulation of CHAC1, GCLC, ZnT2, and MT-like genes in oysters exposed to Cd, and increased ZnT2-like expression following exposure to higher Cd/Zn mixtures. We found evidence of oysters may mobilize metal-related genes to mitigate Cd-induced toxicity by both chelating metals and/or reducing their intracellular concentrations. The observed genes upregulation also indicates their sensitivity to changes in metal bioavailability. Overall, this study offers insights into oyster mechanisms for coping with metal toxicity and suggests ZnT2, MT, CHAC1, and GCLC-like as molecular biomarkers for monitoring aquatic metal pollution using C. gasar as sentinel species.

Pathogens and microorganisms in the mangrove oyster Crassostrea gasar cultivated in an estuarine environment in Northeast Brazil.

Estuaries are important ecosystems due to the ecological services they provide, acting as nurseries for many species of fish and invertebrates, and are also used as environments for the extraction and cultivation of mollusks. Oysters are animals that filter water to obtain oxygen and nutrients. In this process, they can bioaccumulate microorganisms and chemical substances in their tissues. The growth of mollusk culture in Northeastern Brazil requires the health identification of cultivated oysters through the quantification of the potentially harmful microbiota accumulated in the animals. Therefore, the present work aims to quantify and identify bacteria and possible pathogens found in the tissues of cultivated oysters and their culture waters. The Most Probable Number of Coliforms (MPN) in oysters and water were considered suitable according to the Brazilian current legislation, Vibrio sp. obtained low colonization and Salmonella sp. was not observed. The prevalence of microorganisms potentially pathogenic to oysters was 33.7%, highlighting metazoans and Nematopsis sp., however, the intensity of the infestation of these organisms was moderate. The low contamination of oysters demonstrates that this culture environment is promising for this activity. However, continuous environmental and sanitary monitoring is fundamental to guarantee the safety of the culture waters and the sustainability of aquaculture activities.

Analysis of Crassostrea gasar transcriptome reveals candidate genes involved in metal metabolism

Oysters have been extensively employed for monitoring of metal pollution in dynamic aquatic ecosystems. Therefore, the use of specific biomarkers can assist in discriminating the ecotoxicological implications of different elements in such complex environments. In this study, we revisited the sequencing data of gills and digestive glands transcripts in the mangrove oyster Crassostrea gasar and generated a reference transcriptome assembly from multiple assemblers, seven in total. Overall, we were able to identify a total of 11,917 transcripts, with 86.6% of them being functionally annotated and 1.4 times more than the first annotation. We screened the annotated transcripts to identify genes potentially involved in metals' transport, storage, and detoxification. Our findings included genes related to Zn distribution in cells (Zn transporters - ZIP, ZnT), metallothionein (MT-I and MT-IV), GSH biosynthesis, Ca+ transporter (NCX and ATP2B), and Cu distribution in cells (ATP7, ATOX1, CCS, and laccase-like). These results provided a reference transcriptome for additional insights into the transcriptional profile of C. gasar and other bivalves to better understand the molecular pathways underpinning metal tolerance and susceptibility. The study also provided an auxiliary tool for biomonitoring metal contamination in dynamic environments as estuaries.

Survival and growth of mangrove oyster Crassostrea gasar (Dautzenberg, 1891) reared at different depths in ponds in Benin (West Africa)

The objective of this work was to study the survival and growth of juveniles of the oyster Crassostrea gasar reared in ponds at different depths. Rearing trials were carried out for 42 days (6 weeks) in two ponds (12 m2 x 1.10 m deep), one of which was fertilized with poultry droppings and the other with no fertilization. For each pond, 03 depths (30 cm, 60 cm and 90 cm) were tested in duplicate. At each depth, two iron mesh bags (40 cm x 20 cm x 10 cm) were used. Oysters with an average size of 40.50 mm and average weight of 15.36 g were cultivated at a density of 30 individuals per bag. Phytoplankton density, pH, temperature, transparency and salinity of the water were daily measured between 7:00 and 8:00 am. Oysters were counted weekly. Individual length and weight were measured to evaluate their survival and growth. The values of physico-chemical parameters measured during this study met the requirements of tropical water oysters. After 6 weeks of rearing, the best survival rates were observed at 60 cm in the ponds (86.67% and 81.67% in the fertilized and unfertilized ponds, respectively) while the lowest survival (46.67% and 41.67 in the fertilized and unfertilized ponds, respectively) was recorded at 90 cm depth. The highest mean final sizes (40.584 mm and 40.568 mm in the fertilized and unfertilized ponds respectively) were recorded at 60 cm depth while the lowest values (40.557 mm and 40.553 mm in the same order) were recorded at 90 cm depth. The average final weight ranged from1 5.32 g (at 90 cm depth) to 15.38 g (at 60 cm) while it overlapped between 15.3 g (90 cm depth) to 15.35 g (30 cm depth) in the unfertilized pond. The average daily gain was 0.0004 g/day and 0.0005 g/day respectively for the 30 cm and 60 cm depths of the fertilized pond. The best zootechnical performance was recorded between 30 cm and 60 cm depth in the fertilized pond. Fertilized pond culture highlight future prospects for the promotion of Crassostrea gasar oyster culture in controlled environment.

Evaluation of methods for reducing epibionts during farming of the mangrove oyster Crassostrea gasar (Adanson, 1757).

Due to the competition for food, space, oxygen and due to their role as diseases vector, epibionts can negatively affect oyster farming. We assessed the efficacy of six methods commonly used for the removal of epibionts from oyster shells during farming. The experiment was conducted at an oyster farm on the Paraná coast - South Brazil. Oysters (Crassostrea gasar) were acclimated for 90 d in the cultivation system and later exposed to cleaning treatments: i) freshwater; ii) hypersaline water; iii) sodium hypochlorite solution; iv) quaternary ammonia solution; v) exposure to air; vi) hydroblasting; and vii) no cleaning procedure (control). After treatment, oysters were kept in the cultivation system for 15 and 30 d - when the total incrustation and mortality were measured. Epibionts from nine phyla were identified. The most abundant were Arthropoda (Crustacea) (62.5%), Mollusca (33.8%) and Annelida (3.1%). Freshwater [15 (n = 2263 epibionts) and 30 days (n = 2822 epibionts)] and hydroblasting [15 (n = 1850 epibionts) and 30 days (n = 2389 epibionts)] treatments were the most efficient to reduce epibionts and caused lower rates of oyster mortality [15 (5.0 and 3.33%, respectively) and 30 days (1.67 and 6.67%, respectively)].

Salinity and rainfall as inducers of cell proliferation and apoptosis in mangrove oyster Crassostrea gasar spermatogenesis

The present study investigated the influence of physical–chemical​ variables on the development of male gonads, providing information on cell proliferation and apoptosis in cells of the spermatogenic lineage throughout the reproductive cycle. Seeds of oysters of the species Crassostrea gasar from the same population were grown in two cultivation areas with different seawater influences. The area I, located in the municipality of Nova Olinda and area II, in the municipality of Curuçá. The two areas are part of the mangrove coast of the Amazon region and are located approximately 5 and 25 km away from the Atlantic Ocean, respectively. A sample containing 20 specimens of oysters was collected monthly in each of the two areas, and the abiotic parameters were also measured in situ during the collections. Routine histological techniques were used for cell characterization, as well as the classification of gonadal stages and morphometric measurements. Immunohistochemistry was used to access cell proliferation and apoptosis. The abiotic parameters varied constantly during the study, however, precipitation and salinity were the variables that most differed between periods in both areas. The cells of the spermatogenic lineage of C. gasar did not differ from the morphological point of view, however, the analysis of the morphometric parameters showed significant differences both in the cell diameters between maturation periods and between the study areas. Proliferative and apoptotic activities also varied throughout the study, and the quantification of positively labeled cells showed statistically significant differences between the study areas. The animals in the area I showed greater proliferative activity in relation to individuals in area II and using a regression model, we demonstrated that both cell proliferation and apoptosis are related to environmental conditions. It seems likely that animals in area I, exposed to a salinity of ∼25–35, find more favorable environmental conditions for their reproduction since the reduction in cell proliferation observed in area II was negatively related to the salinity of this environment (∼15– 25). Changes in the dynamics of mangrove interstitial waters contribute to changes in the salinity of the environment and can directly impact the physiology of oysters. These findings indicate that oyster farming systems in estuarine environments should be in areas as close to the ocean as possible.

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.

Influence of the proximity to the ocean and seasonality on the growth performance of farmed mangrove oysters (Crassostrea gasar) in tropical environments

In tropical coastal and estuarine environments, such as the mangroves of the Amazon region, salinity is considered to be one of the principal factors limiting the farming of bivalve mollusks. In this context, the present study evaluated the effects of the location of the farm (proximity to the ocean) and seasonality on the growth of the mangrove oyster Crassostrea gasar, and identified the environmental factors that most influenced the growth performance of the oysters over the course of the year. The oysters analyzed in this study were raised over a one-year period on farms in three areas of mangrove on the Brazilian Amazon coast, located at different distances from the ocean. These farms rear oysters using a fixed-tray system. The study period was divided into four seasonal divisions - the rainy-dry transition period, the dry season, dry-rainy transition, and the rainy season. The salinity, pH, temperature, and dissolved oxygen concentration of the water were measured in situ using a multiparameter probe during specimen collection. A mean of 20 specimens were collected each month from each of the three study areas. Once collected, the oysters were weighed and measured. Salinity and precipitation were the environmental parameters that most varied over the course of the study period, with significant differences being found among study areas during this period. The best growth performance was recorded for the farms in areas 1 and 2, which were closest to the ocean, and were significantly different from area 3 (the furthest from the ocean), where the oysters were smallest in size. The evidence indicates that areas located closest to the coast, are the most appropriate for commercial-scale oyster farming, while areas furthest from the ocean and influenced primarily by fluvial discharge, is much less favorable for the production of oysters. Overall, the data showed that, when raised in its natural environment, C. gasar presents a better growth performance during the rainy-dry transition period and the dry season, especially on farms located close to the coast, where salinity is between 25 and 35, given that this condition favors the development of the oysters, and optimizes their growth performance in commercial scale farming operations.

Effects of salinity on fertilization and larviculture of the mangrove oyster, Crassostrea gasar in the laboratory

The mangrove oyster Crassostrea gasar is the main native oyster species cultivated in Brazil. C. gasar culture is based on seed and juvenile capture from the environment. However, its capture using artificial collectors is difficult due to overlapping settlement periods with other oyster species. Therefore, research on seed production techniques of C. gasar in hatcheries is needed. This study evaluated the effect of salinity on fertilization and larviculture of C. gasar in salinities 7, 14, 21, 28 and 35 from December 2013 to April 2014. Fertilization and larva-D development occurred between salinities 21 and 35. Larval development from larva-D to umbo occurred with no significant differences in length and height between salinities 14 and 35. Only larvae cultivated in salinities 28 and 35 reached the settlement stage by the end of the experiment, after 25days of larviculture. Fertilization, embryonic and larval development presented best results in salinity 28.

Bioconcentration of Ag, Cd, Co, Mn and Zn in the Mangrove Oyster (Crassostrea gasar) and Preliminary Human Health Risk Assessment: A Radiotracer Study.

Bioaccumulation kinetics of five dissolved metals were determined in the mangrove oyster Crassostrea gasar, using corresponding radiotracers ((54)Mn, (57)Co, (65)Zn, (109)Cd and (110m)Ag). Additionally, their bioaccessibility to human consumers was estimated. Results indicated that over a 14-day exposure (54)Mn and (57)Co were linearly concentrated in oysters whereas (109)Cd, (65)Zn and (110m)Ag were starting to saturate (steady-state not reached). Whole-body concentration factors at 14days (CF14d in toto) ranged from 187±65 to 629±179 with the lowest bioconcentration capacity for Co and the highest for Ag. Depuration kinetics were best described by a double-exponential model with associated biological half-lives ranging from 26days (Ag) to almost 8months (Zn and Cd). Bioaccessible fraction of the studied elements was estimated using in vitro digestions, which suggested that oysters consumed seasoned with lemon enhanced the accessibility of Cd, Mn and Zn to human consumers, but not Ag and Co.

A Status Assessment of Perkinsiosis, Bonamiosis, and Mateiliosis in Commercial Marine Bivalves from Southern Brazil

ABSTRACT The protozoans Perkinsus marinus, Perkinsus olseni, Bonamia ostreae, Bonamia exitiosa, and Marteilia refringens are responsible for some of the most detrimental diseases in the production of cultivated shellfish worldwide and are classified as notifiable diseases by the World Organization for Animal Health (OIE). This study examined the general health status of wild and cultured bivalves from southern Brazil and included diagnostic tests for the presence of Perkinsus sp., Bonamia sp., andMarteilia sp. Cultured bivalves included the mangrove oyster Crassostrea gasar (syn. Crassostrea brasiliana), the brown mussel Perna perna, the lion's paw scallop Nodipecten nodosus, andwing pearl oyster Pteria hirundo. Themangrove oyster Crassostrea rhizophorae and the carib pointed venus clam Anomalocardia brasiliana (syn. Anomalocardia flexuosa) were collected from wild populations. A variety of parasitic or commensal organisms were detected by histology including Ancistrocoma-like and Spenophrya-like organism...

Detection of a parasitic amoeba (Order Dactylopodida) in the female gonads of oysters in Brazil.

The impacts of oocyte parasites on the reproductive success of molluscs are largely unknown. In this study, we evaluated the presence of gonad parasites in 6 species of marine bivalve molluscs native to southern Brazil. Cultured bivalves included the mangrove oyster Crassostrea gasar (sometimes called C. brasiliana), the brown mussel Perna perna, the lion's paw scallop Nodipecten nodosus and the wing pearl oyster Pteria hirundo. Another species of mangrove oyster, C. rhizophorae, and the carib pointed venus clam Anomalocardia brasiliana (syn. A. flexuosa) were collected from the wild. Molluscs were collected in winter 2009 and summer 2010 for histopathological and molecular evaluation. An unknown ovarian parasite (UOP) was observed in histopathological sections of female gonads of C. gasar and C. rhizophorae. The UOP possessed features suggestive of amoebae, including an irregular outer membrane, frothy cytoplasm, a nucleus with a prominent central nucleolus and a closely associated basophilic parasome. PCR analysis was negative for Marteilioides chungmuensis, Perkinsus spp. and Paramoeba perurans. However, real-time PCR successfully amplified DNA from oyster gonads when using universal Paramoeba spp. primers. Also, conventional PCR amplified DNA using primers specific for Perkinsela amoebae-like organisms (syn. Perkinsiella), which are considered as endosymbionts of Parameoba spp., previously thought to be the parasome. Our results suggest that this UOP is a species of amoeba belonging to 1 of the 2 families of the order Dactylopodida, possibly related to Paramoeba spp. This study represents the first report of this type of organism in oysters. We found that C. gasar and C. rhizophorae were the most susceptible molluscs to these UOPs.

Maturation of the Mangrove OysterCrassostrea gasarat Different Temperatures in the Laboratory

ABSTRACT This study assessed the influence of temperature on gonadal tissue maturation in the mangrove oyster Crassostrea gasar in the laboratory. The oysters were held at three water temperatures (18°C, 22°C, and 26°C), and the control oysters were maintained under cultivation in the environment. Every 10 days, 10 oysters from each treatment were examined for condition index and 10 for histological analysis. In the 22°C, 26°C, and field treatments, gonadal tissue maturation was observed, with no significant difference among treatments. The 18°C treatment was significantly different compared with the groups maintained at other temperatures, but did not demonstrate an improvement in gonadal tissue maturation. The results suggest that at 18°C, an accumulation of energy reserves occurs, and at temperatures greater than 22°C, gamete maturation occurs. In this study, the animals maintained in the field environment exhibited the same maturation conditions as those maintained in the laboratory, suggesting that t...

Growth of Crassostrea gasar cultured in marine and estuary environments in Brazilian waters

The objective of this work was to evaluate the growth of the mangrove oyster Crassostrea gasar cultured in marine and estuarine environments. Oysters were cultured for 11 months in a longline system in two study sites - São Francisco do Sul and Florianópolis -, in the state of Santa Catarina, Southern Brazil. Water chlorophyll-α concentration, temperature, and salinity were measured weekly. The oysters were measured monthly (shell size and weight gain) to assess growth. At the end of the culture period, the average wet flesh weight, dry flesh weight, and shell weight were determined, as well as the distribution of oysters per size class. Six nonlinear models (logistic, exponential, Gompertz, Brody, Richards, and Von Bertalanffy) were adjusted to the oyster growth data set. Final mean shell sizes were higher in São Francisco do Sul than in Florianópolis. In addition, oysters cultured in São Francisco do Sul were more uniformly distributed in the four size classes than those cultured in Florianópolis. The highest average values of wet flesh weight and shell weight were observed in São Francisco do Sul, whereas dry flesh weight did not differ between the sites. The estuary environment is more promising for the cultivation of oysters.

Immunological responses of the mangrove oysters Crassostrea gasar naturally infected by Perkinsus sp. in the Mamanguape Estuary, Paraíba state (Northeastern, Brazil)

Perkinsus genus includes protozoan parasites of marine mollusks, especially bivalves. In the last four years, this parasite has been detected in mangrove oysters Crassostrea rhizophorae and Crassostrea gasar from the Northeastern region of Brazil. Hemocytes are the key cells of the oyster immune system, being responsible for a variety of cellular and humoral reactions, such as phagocytosis, encapsulation and the release of several effector molecules that control the invasion and proliferation of microorganisms. In Brazil, there is little information on perkinsosis and none on the immune responses of native oysters' species against Perkinsus spp. The objective of this study was to determine the effects of natural infection by Perkinsus sp. on the immunological parameters of mangrove oysters C. gasar cultured in the Mamanguape River Estuary (Paraíba, Brazil). Adults oysters (N = 40/month) were sampled in December 2011, March, May, August and October 2012. Gills were removed and used to determine the presence and intensity of the Perkinsus sp. infection, according to a scale of four levels (1–4), using the Ray's fluid thioglycollate medium assay. Immunological parameters were measured in hemolymph samples by flow cytometry, including: total hemocyte count (THC), differential hemocyte count (DHC), cell mortality, phagocytic capacity, and production of Reactive Oxygen Species (ROS). The plasma was used to determine the hemagglutination activity. The results showed the occurrence of Perkinsus sp. with the highest mean prevalence (93.3%) seen so far in oyster populations in Brazil. Despite that, no oyster mortality was associated. In contrast, we observed an increase in hemocyte mortality and a suppression of two of the main defense mechanisms, phagocytosis and ROS production in infected oysters. The increase in the percentage of blast-like cells on the hemolymph, and the increase in THC in oysters heavily infected (at the maximum intensity, 4) suggest an induction of hemocytes proliferation. The immunological parameters varied over the studied months, which may be attributed to the dynamics of infection by Perkinsus sp. The results of the present study demonstrate that Perkinsus sp. has a deleterious effect on C. gasar immune system, mainly in high intensities, which likely renders oysters more susceptible to other pathogens and diseases.