Mangrove Oyster Crassostrea Rhizophorae Research Articles

Reproductive cycle of the mangrove oyster Crassostrea rhizophorae (Guilding, 1828) in Delta do Parnaíba, Brazil

This study describes some aspects of the reproductive biology of the native oyster Crassostrea rhizophorae in the Delta do Parnaíba estuary, located between the states of Maranhão and Piauí, Brazil. The oysters were acquired from landings at Porto dos Tatus (Ilha Grande - PI) between June 2017 and May 2018. Approximately 50 individuals per month (n=611) with an average total shell length of 74.44 mm (±14.31 SD) were collected for analysis of gonadal development and condition index and correlated with temporal variations in local rainfall. The C. rhizophorae population in the Parnaíba Delta estuary showed a sex ratio of 2.18 females to 1 male and continuous reproduction. The condition index (CI) values in the dry period were higher, coinciding with a greater proportion of individuals in the gametogenesis and pre-spawning stages. In the rainy season, there was a reduction in the CI as a result of animals in the gamete release stage.

Fatty acid contribution of microalgal diets on spat performance of the tropical mangrove oyster Crassostrea rhizophorae, in Mochima Bay, Venezuela

Fatty acids play a fundamental role in the ecology and growth of many invertebrates, such as filter-feeder bivalve. To guarantee adequate nutrition during transfer from the nursery to the natural environment, we studied the survival, growth and fatty acid (FA) profile of Crassostrea rhizophorae oyster spat fed with seven microalgae combinations of Chaetoceros sp. Araya strain (Ch-A), Tisochrysis lutea (Tl) and Tetraselmis chuii (Tc). The diets included three monoalgal diets (Ch-A, Tl and Tc), three binary combinations (Tl+Ch-A, Tl+Tc and Ch-A+Tc) and one ternary mixture (Tc+Ch-A+Tl). Groups of triplicated carboys each containing 21 oyster spat were used to test the experimental diets, while an additional group was deployed directly in the environment as a control. After 36 days, total lipids, FA profiles and biometric parameters of the spat were analyzed.​ The spat were then transferred to the outdoor environment, and cultivated under suspension conditions for 30 additional days. At the end of this period, FA profiles and growth were again determined. Environmental variables were sampled weekly. Highest shell height growth and soft tissues mass were observed in the spat fed with Ch-A in any combination: the mono-algae Ch-A diet, the binary Ch-A+Tc and Ch-A+Tl diets, a tendency that persisted in the outdoor environment. Our results showed lower shell and soft tissues mass growth, and a drop in the levels of certain FAs of the spat after their transfer to the natural environment, such as 14:0, 16:1n-7, 18:1n-9, 18:4n-3 and 20:5n-3 FA. This effect probably reflected a compensation strategy for the scarce availability of food and higher temperatures observed in the natural environment.

Maximum Tolerable Intake of Mangrove Oyster (Crassostrea rhizophorae) from the Tapak River, Semarang City, Indonesia, which Contains Cd and Pb Metals

Mangrove oysters are a type of oyster typical for human consumption in Semarang City. The Tapak River in Semarang is a popular fishing ground for mangrove oysters, but it is also contaminated with cadmium (Cd) and lead (Pb) metals. This research was determined to analyze the concentration of Cd and Pb metals in mangrove oyster meat from the Tapak River and determine the maximum tolerable intake for humans. Oysters were collected from 3 stations with 3 replicates per station. Metal concentrations in mangrove oyster meat were analyzed with a wet digestion method followed by atomic absorption spectrophotometry. Most of the meat samples contained Cd exceeding standard concentrations for shellfish and all meat samples contained Pb exceeding the standard concentrations for shellfish. The maximum tolerable intake of Cd and Pb for human adults is 0.954 ± 0.431 mg week-1 and 0.164 ± 0.014 mg week-1 respectively.

Dead men still tell tales: bivalve death assemblages record dynamics and consequences of recent biological invasions in Kingston Harbour, Jamaica

Abstract Short-lived biological invasions may leave lasting impacts on ecosystems well after they have concluded, yet the nature of such events is difficult to elucidate in the absence of monitoring efforts. Here, the ability for surficial death assemblages to recount such invasion events and their ecological legacies was tested using mangrove-dwelling bivalves from Kingston Harbour, Jamaica, where the Asian green mussel ( Perna viridis ) was introduced c. 20 years ago. While rare in Kingston Harbour today, relative densities of dead P. viridis shells mapped well to historical surveys from early into the invasion and thus help reconstruct spatial variations in invasion intensity. Live–dead discordance for the bivalve community further indicated that species have not returned to pre-invasion relative abundance distributions such that the economically-important mangrove oyster ( Crassostrea rhizophorae ) declined while the flat tree oyster ( Isognomon alatus ) rose to dominance. Finally, we report the presence of the charru mussel ( Mytella strigata ) in Kingston Harbour, a newly introduced species that has not yet been significantly incorporated into the subfossil record. This case study exemplifies the utility of underexploited sources of geohistorical data for informing the growing problem of human-assisted biological invasion.

Biological responses of mangrove oysters (Crassostrea rhizophorae) and mercury contamination in an urban tropical estuary

This study aimed to assess the biological responses of oysters from an urban estuary in Northeast Brazil, through the evaluation of biochemical and physiological biomarkers, and integrate these responses with the investigation of mercury seasonal contamination. Oysters and sediment were collected from three sites in the estuary of the Ceará River during dry and rainy seasons. Biomarkers (AchE, CaE, GST, CAT, and Condition Index) were analyzed in different tissues. Hg bioaccumulation was higher in animals sampled in the rainy season, with increases varying from 5% to 136%, compared to the dry season. The changes in biomarkers highlight already elevated stresses for the organisms at the inner portion of the estuary, near the confluence with the Maranguapinho River, mainly during the rainy season, corroborating other studies that showed ecotoxicological effects with water and sediment samples. Finally, no correlation between Hg in sediment/oyster and biomarker results was observed.

Seasonal variation of oxidative biomarkers in gills and digestive glands of the clam Anomalocardia flexuosa and the mangrove oyster Crassostrea rhizophorae

We determined values of antioxidant biomarkers catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione S-transferase (GST) and malondialdehyde (MDA) in two bivalve species from a subtropical system in Brazil. Differences in the biomarkers activities measured in digestive glands and gills sampled at two seasons and in sites with different levels of contamination were tested using univariate and multivariate analyses. Seasonality was the main factor accounting for overall variability. Significant SOD and GPx activities and increased levels of lipid peroxides were detected in summer, while CAT activity was higher in winter. However, biomarkers respond to complex environmental settings as indicated by the significant interaction between season and contamination level. We propose A. flexuosa as a candidate for monitoring studies with sampling occurring at a yearly timescale, and using C. rhizophorae is better suited for designs that include both seasons.

Capacity of tissue water regulation is impaired in an osmoconformer living in impacted estuaries?

Estuarine osmoconformes rely on their ability to perform tissue and cell water regulation to cope with daily osmotic challenges that occur in the estuary. In addition, these animals currently must deal with pollutants present in the estuarine environment, which can disturb their capacity of water regulation. We collected the mangrove oyster Crassostrea rhizophorae in two tropical estuaries in the Northeast region of Brazil with different degrees of human interference: the Paraíba Estuary (impacted) and the Mamanguape Estuary (preserved). Tissue water content was analyzed after exposure to salinities 12, 24 and 36 for 24 h. Gill cell volume regulation was analyzed in vitro upon hypo- and hyper-osmotic conditions. We also analyzed gill MXR (multi-xenobiotic resistance) mechanism, as reference of environmental pollution. Gill and muscle of oysters from two sites of Paraíba Estuary, and from one site of Mamanguape Estuary were not able to maintain tissue water content upon hypo- and hyper-osmotic conditions. Gill cells of oyster from the same sites exhibited swelling followed by regulatory volume decrease upon hypo-osmotic condition. Gill MXR activity was increased in oysters from these sites. The best tissue and cell water regulation, and the lowest MXR activity, was found in oyster from downstream of Mamanguape Estuary, our reference site and the one most preserved. Tissue and cell water regulation proved to be a sensitive parameter to environmental pollution and could be considered as biomarker of aquatic contamination.

Bacteriological Quality of the Mangrove Oyster (Crassostrea rhizophorae) in the Swamp of Mestizo - Cordoba (Colombia)

Objectives: To determine the bacteriological quality of the mangrove oyster and its aquatic environment, such as a risk factor in public health, through the consumption of these products from the natural environment. Materials and Methods: Data were collected about 60 samples of oysters and the surrounding water, between June and November 2004. Using the indirect method of counting multiple fermentation tubes, we estimated the concentration of bacteria indicators of total and fecal coliform contamination. The indicators of the bacteriological quality of the oysters presented a minimum of ≤ 3 NMP.100 mL-1 and a maximum of 46 × 104 MPN.100 mL-1 of total coliforms, fecal coliforms showed a seasonal variation in concentrations between ≤3 NMP.100 mL-1 and 2 × 103 MPN.100 mL-1 . Findings: The analysis of water samples recorded a range of concentration of coliforms from ≤ 3 NMP.100 mL-1 to 3.9 × 105 NMP.100 mL-1 and for fecal coliforms it ranged from ≤ 3 NMP.100 mL-1 to 7 × 103 MPN.100 mL-1 . This study suggests that there exists a directly proportional relationship between the bacteriological quality of the mangrove oyster Crassostrea rhizophorae and the water quality of the environment, by its status filtering, which contributes a factor of risk to public health, the consumption of this food, especially if the consumption is done in a direct way. Applications/recommendations: the potentiality of the Bay of Mestizo, Colombia, for the development of a sustainable aquaculture of the mangrove oyster (Crassostrea rhizophorae), requires baseline studies on various environmental and social aspects which will lay the basis for the socio-economic development of this region. Keywords: Molluscs, total coliforms, fecal coliforms, sustainable aquaculture, public health.

Composición de la comunidad bioincrustante de un cultivo de ostras tropicales en un estuario del Amazonas, Estado de Pará, Norte de Brasil

Biofouling affects global aquaculture with significant impacts on productivity and profitability, especially in marine shellfish culture, where both the target culture species and/or infrastructure are exposed to a diverse array of fouling organisms. In oyster culture, fouling of stock causes physical damage, mechanical interference, biological competition and environmental modification, with infrastructure also colonized. The present study describes the composition of the biofouling community inhabiting the surface of the mangrove oyster Crassostrea rhizophorae , cultivated in an Amazon estuary, in the state of Para, northern Brazil. In total, 6,124 macroinvertebrates were collected during July, August, October and December 2013. Collected epifauna was represented by 5 groups (Bivalvia, Gastropoda, Polychaeta, Crustacea and Anthozoa), 20 families and 37 species. Bivalvia was the most abundant class, with the mussel Mytella charruana by far the most dominant species with 5,183 individuals. Knowledge about the composition of biofouling as well as identifying the main species that cause direct impacts allows more tailored and strategic management options, minimizing the often-significant costs associated with biofouling control (antifouling)

Acetylcholinesterase of mangrove oyster Crassostrea rhizophorae: A highly thermostable enzyme with promising features for estuarine biomonitoring

Enzyme biomarkers from several aquatic organisms have been used for assessing the exposure to contaminants at sublethal levels. Amongst them, the cholinesterases are commonly extracted from several organisms to evaluate/measure organophosphate and carbamate neurotoxic effects. Acetylcholinesterase (AChE; EC 3.1.1.7) is an enzyme of the group of serine esterases that acts on the hydrolysis of the neurotransmitter acetylcholine allowing the intermittence of the nerve impulses responsible for the neuronal communication. This enzyme is the main target for the action of some pesticides and the inhibition of its activity in bivalve mollusks may be used as biomarker due to their filter-feeding habit. In this context, the present study aimed to characterize physicochemical and kinetic parameters of the AChE extracted from gills and viscera of the oyster Crassostrea rhizophorae and investigate the in vitro effect of pesticides (dichlorvos, diazinon, chlorpyrifos, methyl-parathion, temephos, carbaryl, carbofuran, aldicarb, diflubenzuron and novaluron) in search for assessing its potential as biomarker. Specific substrates and inhibitors evidenced the predominance of AChE in both tissues. The optimum pH found for gills and viscera AChE were 8.0 and 8.5, respectively. The maximum peak of activity occurred at 70 °C for gill AChE and 75 °C for viscera AChE. The enzymes of both tissues presented remarkable thermostability. The Michaelis-Menten constant for both enzymes were 1.32 ± 0.20 mM for gills and 0.43 ± 0.12 mM for viscera. The Vmax values for gills and viscera were 53.57 ± 1.72 and 27.71 ± 1.15 mU/mg, respectively. The enzymes were able to reduce the activation energy to 9.75 kcal mol−1 (gills) and 11.87 kcal mol−1 (viscera) obtaining rate enhancements of 3.57 × 105 and 1.01 × 104, respectively, in relation to non-catalyzed reactions. Among the pesticides under study, the carbamates carbaryl and carbofuran exerted the strongest inhibitory effects on the enzyme activity achieving important degrees of inhibition at concentrations below national and international current regulations. The first observation of the effects of benzoylurea pesticides (diflubenzuron and novaluron) on AChE from mollusks is reported here. The gills AChE of C. rhizophorae showed potential to be specific biomarker for the carbamate carbaryl while the viscera AChE showed it for carbofuran. According to their features, these enzymes may be proposed as promising tools for estuarine monitoring as well as biocomponent of biosensor devices.

Hemolymph and gill carbonic anhydrase are more sensitive to aquatic contamination than mantle carbonic anhydrase in the mangrove oyster Crassostrea rhizophorae

Carbonic anhydrase (CA) is a ubiquitous metalloenzyme of great importance in several physiological processes. Due to its physiological importance and sensitivity to various pollutants, CA activity has been used as biomarker of aquatic contamination. Considering that in bivalves the sensitivity of CA to pollutants seems to be tissue-specific, we proposed here to analyze CA activity of hemolymph, gill and mantle of Crassostrea rhizophorae collected in two tropical Brazilian estuaries with different levels of anthropogenic impact, in dry and rainy season. We found increased carbonic anhydrase activity in hemolymph, gill and mantle of oysters collected in the Paraíba Estuary (a site of high anthropogenic impact) when compared to oysters from Mamanguape Estuary (inserted in an area of environmental preservation), especially in the rainy season. CA of hemolymph and gill were more sensitive than mantle CA to aquatic contamination. This study enhances the suitability of carbonic anhydrase activity for field biomarker applications with bivalves and brings new and relevant information on hemolymph carbonic anhydrase activity as biomarker of aquatic contamination.

Potential of sites in northern Cuba for developing an industry of the native mangrove oyster (Crassostrea rhizophorae)

Mangrove oysters ( Crassostrea rhizophorae ) were collected and raised for seven months at four sites (Punta Pargo, Jorobado, Canete, and Enfermeria) around Bahia Sagua La Grande on the north coast of Cuba, to determine which site offered the best conditions for cultivation of this commercially important species. Monthly measurements of oyster height were taken on 30 oysters randomly collected from each study site. Only oysters raised at Punta Pargo and Enfermeria reached the mean commercial size (>40 mm) within the study period; these oysters were significantly larger than oysters raised at Canete and Jorobado. No significant differences in survival between the sites were observed. Punta Pargo and Enfermeria showed the best potential for oyster farming in the Bahia de Sagua area. Despite human impact on runoff caused by damming of the adjacent river, water quality remains acceptable for oyster cultivation. With proper stock management and production of selected fast-growing oysters in hatcheries, oyster farming can become an important aquaculture industry in Cuba.

TOXICIDADE DE EFLUENTES DE VIVEIRO DE CAMARÃO: PERSPECTIVAS PARA ANÁLISE DE RISCOS E TOMADA DE DECISÕES

A carcinicultura, na última década cresceu, no mundo acima da média das atividades agrárias e, c omo qualquer atividade antrópica, tem impactado de diferentes formas os locais da sua instalação. Pouca pesquisa científica tem sido produzida visando à sua mitigação, em especial quanto a avaliação dos impactos causados pelos efluentes da atividade. Assim, os objetivos deste trabalho foram avaliar a toxicidade dos efluentes de viveiros de camarão durante a drenagem para despesca, verificar existência de diferenças na qualidade da água entre os vários estratos da coluna d’água. A metodologia utilizou testes de toxicidade efetuados com embriões da ostra Crassostrea rhizophorae , buscando relacionar as possíveis anormalidades com os valores de parâmetros físico-químicos medidos em amostras dos efluentes. Os bioensaios com embriões demonstraram a ocorrência de toxicidade dos efluentes sobre os organismos e comprovaram , que juntamente com a análise dos parâmetros físico-químicos, contribuem para uma melhor avaliação da qualidade da água de cultivo. Os resultados também mostraram a existência de um gradiente de qualidade ao longo da coluna d’água dos viveiros de camarão, sendo que o estrato de superfície apresentou melhor qualidade que o estrato de fundo.

Identificación del ostión americano Crassostrea virginica (Mollusca: Bivalvia: Ostreidae) como recurso natural en las Antillas Mayores: Cuba

The mangrove oyster Crassostrea rhizophorae (Guilding, 1828) is the only native species of oyster marketed in Cuba. However, oyster beds (known locally as “bottom oyster”) were found in the mouth of the Cuyaguateje and Cauto Rivers, with a different morphology and occupying a different habitat with respect to C. rhizophorae. These also contribute to oyster production in Cuba. We addressed studies for phenotypic characterization of both oysters found in 3 areas surrounding these 2 rivers, finding evidence of phenotypic and habitat dichotomies of the bottom oyster from the mangrove oyster. We conclude that Crassostrea virginica (Gmelin, 1791) is the species called “bottom-oyster”. Its average size is 61.1±23.46mm and reaches a maximum length of 145mm), which is 65% larger than the mangrove oyster C. rhizophorae (average 37.2±11.95mm, maximum 87mm) and has higher meat yield (4.5-10.2% meat of total weight) than populations of the mangrove oyster (3.9 to 7.1%). This study is the first report of C. virginica available as a natural resource for commercial exploitation in Cuba. Its excellent performance recommends it for cultivation in the Greater Antilles.

Crecimiento y madurez sexual de Crassostrea rhizophorae (Guilding, 1828) cultivada en sistema suspendido en Estero Vizcaya, Limón, Costa Rica

A study of mangrove oysters (Crassostrea rhizophorae) cultured in a raft system between January and June 1982 in the Vizcaya Tideland, Limon, Costa Rica showed that the rates of growth were higher for the first three months of culture, decreasing gradually in the next three months. An average length of 65.83 mm with a maximum of 85.50 mm was reached at the sixth month. Strong correlation was observed between total live weight and total length.The minimal sexual maturity size was 13 mm with an approximate age between 15 and 22 days; spawning was not observed in individuals smaller than 21 mm.

CONDICION BACTERIOLOGICA DE LAS OSTRA DEL MANGLAR (Crassostrea rhizophorae Guilding) EN LA CIENAGA GRANDE DE SANTA MARTA, CARIBE COLOMBIANO

Between June 1985 and March 1986 the bacteriological condition of 20 samples of the mangrove oyster (Crassostrea rhizophorae) from two growing areas located in the Ciénaga Grande de Santa Marta was monitored; one of the areas was next to a village and the other far away any human concentration. In both locations the levels of faecal pollution present in the water and in the oysters usually surpasse the safety levels determined by international regulations, being a high potential risk for human health. The unsatisfactory condition of the bivalves comes from the steady flow of sewages produced in the lacustrine villages and in the basin as a whole.

ASPECTOS BIOLOGICOS Y ECOLOGICOS DE MYTILOPSIS SALLEI (RECLUZ1849) (BIVALVIA: DREISSENIDAE) EN BANCOS DE OSTRA DE LA CIENAGA GRANDE DE SANTA MARTA, CARIBE COLOMBIANO

Mytilopsis sallei is a widely distributed species living on hard substrata in the Ciénaga Grande de Santa Marta, where it is particularly abundant on mangrove oyster (Crassostrea rhizophorae) reefs reaching densities of 5000 individuals/m2 . Even though it has wide salinity and temperature tolerances, it prefers those places such as mouths of rivers, where fresh-water supply is constant. It can also withstand turbid waters with a high sediment load. There is no competition between M.sallei and the oyster C. rhizophorae, even in heavily-exploited reefs, because of the environmental preferences of each species and the high productivity of Ciénaga's waters assuring a constant food offer for filtering species. M. sallei has separate sexes; males dominate the population. Ripe individuals are found all year-long, but two periods per year of increased reproductive activity and settlement occur, associated to drastic salinity changes: a major one from October to November {rainy season) and a second of lesser importance from March to April (dry season). Juveniles grow steadily; as they attain greater size growth is minimal. Growth and development of these populations seem to be controlled by the influx of fresh water, the high predation rates and relatively low availability of hard substrata.

Perkinsus sp. infecting the oyster Crassostrea rhizophorae from estuaries of the septentrional Northeast, Brazil.

The mangrove oyster Crassostrea rhizophorae is an estuarine resource exploited by riverside communities in Northeast Brazil. Despite its socioeconomic importance, studies on the health status of this bivalve are scanty in this region. The purpose of the present study was to investigate the presence of the protozoan Perkinsus sp. in C. rhizophorae collected in August and September 2011 in three estuaries of the septentrional Northeast, Brazil: Jaguaribe (Ceará), Camurupim (Piauí) and Carnaubeiras (Maranhão) (n= 150 specimens/site). The samples were submitted to Ray's fluid thioglycollate medium (RFTM), PCR and histology assays. The RFTM assay revealed spherical, blue or bluish-black hypnospores of the genus Perkinsus in 50 specimens (Jaguaribe= 17.3%, Camurupim= 5.3%, Carnaubeiras= 10.6%). The intensity of the infection ranged from very light (1-10 cells per slide) to severe (more than 40 cells in each of 10 fields of the slide) for Jaguaribe; very light for Camurupim and very light to moderate (at least 40 cells observed in each of 10 fields of the slide) for Carnaubeiras. When submitted to confirmatory PCR analysis, 6 cases were confirmed (Jaguaribe=3, Camurupim=1, Carnaubeiras=2). The histology confirmed 21 cases of infection in specimens from the three estuaries. Although local collectors have reported no mortality in oyster populations that might be attributed to infection by Perkinsus, health surveillance of oyster populations in the septentrional region of Northeast Brazil is advisable.

Assessing the genetic diversity of the mangrove oyster Crassostrea rhizophorae (Bivalvia, Ostreidae) by microsatellite markers in southeastern Brazil

Oysters of the genus Crassostrea are an economically important resource occurring along the Brazilian coast, mainly in estuarine regions. Inter- and intra-population genetic diversity is essential for monitoring long-term genetic changes and for sustainable use of this bivalve by coastal fishing communities. Microsatellite markers were used to evaluate the genetic diversity of natural populations of the mangrove oyster Crassostrea rhizophorae in southeastern Brazil. Samples of 150 oysters from four areas were analyzed. Microsatellite loci were obtained from an enriched microsatellite library. The genetic structure was evaluated using an index of genetic differentiation described previously. The effective population size and rate of gene flow were estimated through a maximum likelihood coalescent approach using Migrate. The mean number of alleles ranged from 10 to 21 and the expected heterozygosity from 0.89 to 0.91. Evidence of a possible bottleneck effect under three mutational models was found. The Dest index indicated low to moderate differentiation among sample locales. Coalescent analysis showed variation in effective population size and asymmetry in the gene flow among samples. Levels of genetic variability and differentiation found among C. rhizophorae populated banks have important implications for the sustainable harvest, cultivation and conservation of this marine resource in the studied area.

Parasites in the mangrove oyster Crassostrea rhizophorae cultivated in the estuary of the Graciosa River in Taperoá, Bahia.

In this work, parasites associated with the mangrove oyster Crassostrea rhizophorae were studied at a cultivation unit in the estuary of the Graciosa River in Taperoá, Bahia. On a monthly basis, between April 2011 and March 2012, 20 oysters were collected, measured and fixed in 10% formaldehyde. In order to identify the parasites, routine histological techniques were used. The specimens were embedded in paraffin and sections, 7 µm thick, were cut. These were then stained with Harris hematoxylin and eosin and were examined using an optical microscope. The parameters analyzed to investigate water quality showed that the temperature ranged from 23.9 °C to 29.3 °C, water salinity from 0.4 to 24.2 Practical Salinity Units PSU and recorded rainfall from 80 mm to 406.4 mm/month. During the parasitological analyses, infestation of the polychaete Neanthes succinea was observed in 41% of the oysters. Through histological techniques, the following parasites were identified: colonies of Rickettsia-like organisms (RLOs); the protozoa Nematopsis sp. and Ancistrocoma sp.; the turbellarian Urastoma sp.; the metacestode Tylocephalum sp. and an unidentified tapeworm. The data collected showed that there was low-intensity infection with and prevalence of parasites, except for Nematopsis sp., thus attesting that these cultivated oysters were in a healthy condition.