Crassostrea Gasar Research Articles

Minerals and Trace Elements Content of Selected Shellfish from Opuro-ama Waterfront: An Impacted Tidal Creek in Rivers State, Nigeria

In this study, the content of essential minerals, copper (Cu), iron (Fe), manganese (Mn), calcium (Ca), and sodium (Na) in the edible parts of Tympanotonus fuscatus, Thais coronata, Crassostrea gasar, Cardisoma guanhumi and Callinectes amnicola from Opuro-ama creeks, River’s state were analyzed using Atomic Absorption Spectrophotometer and descriptive statistical analyses of variance were done using SPSS and significant means were separated using the Duncan multiple range test at 0.05. High Cu content was found in the T. coronata (9.66mg/g) while the lowest was observed in C. amnicola (0.54mg/g). Fe was higher in C. gasar (37.8mg/g) and the lowest in T. fuscatus (6.78mg/g). The concentration of Manganese was highest in C. guanhumi (144.8mg/g) and least T. fuscatus in (15.9mg/g). C. guanhumi recorded the highest (225.1mg/g) Ca content while the least was observed in T. fuscatus (55.8mg/g). T. coronata recorded the highest (2.11mg/g) Na content while the least was found in T. fuscatus (0.22mg/g). Ca was the highest mineral observed in all five shellfish, and the least was Sodium (Ca >Mn.>Fe>Cu>Na). The Physico-chemical parameters such as Temperature (°C), pH, Salinity (ppt), DO (Mgl-1), BOD (Mgl-1) and Conductivity (µS/ cm) observed during the study were all within the acceptable limits of the World Health Organization (WHO), Department of Petroleum Resources (DPR) and Federal Environmental Protection Agency (FEPA). The five shellfish species from the Opuro-ama creeks were shown to be good sources of nutrients at various levels, therefore might be a useful alternative for other materials for animal feed formulation

Climate Resilience and Adaptation in West African Oyster Fisheries: An Expert-Based Assessment of the Vulnerability of the Oyster Crassostrea tulipa to Climate Change

Globally, over 85% of oyster reefs have been lost, and the combined effects of climate change, ocean acidification, and environmental degradation, including pollution and mangrove overharvesting, could further reduce global oyster fisheries in the coming decades. To understand the level of impact of climate change on the oyster fishery in West Africa, an expert-based vulnerability assessment to climate change was conducted for the West African mangrove oyster (Crassostrea tulipa, Lamarck 1819). Using a combination of the exposure of the oyster to climatic stressors (estuarine temperature, salinity, river flow, surface run-off, sea level rise, and estuarine circulation) together with an assessment of sensitivity to these stressors, we estimate the overall vulnerability of C. tulipa to climate change. A very high overall climate vulnerability score of 12 on a scale of 16 was calculated for C. tulipa. While the overall climate exposure score in the West African coastal region remained high, the high sensitivity of C. tulipa to hydrographic conditions of its habitat, in particular salinity, coupled with its sessile and habitat-specific nature, pushed the overall vulnerability to very high. Early life history settlement requirements, adult mobility, and sensitivity to salinity were the three most important biological and sensitivity attributes that determined the vulnerability score. By leaving each of these three sensitivity attributes out of the analysis, the overall vulnerability score was reduced to 9 (i.e., from very high to high). A negative directional effect of climate change, coupled with a low potential for change in distribution, threatens the C. tulipa fishery in a long-term adverse climate scenario. We recommend management efforts that incorporate climate resilience and adaptation practices to prioritize recruitment success, as well as the development of breeding lines with climate-resilient traits.

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.

Cardiac responses in Crassostrea gasar: An experimental approach of how the tidal cycle influences the heart function of the mangrove oyster

Cardiac physiological studies in oysters are scarce and these kinds of responses can be key issues for understanding behavioral and baseline adaptive responses. In this study we characterized the electrocardiogram (ECG) tracing patterns, wave intervals (RR; QT), and complex duration (QRS) of Crassostrea gasar during immersion followed by air exposure, simulating what occurs in a tide cycle. Initially, the ECG was analyzed in the oysters under immersion for 30 min to evaluate the basal recordings (immersion exposure condition). Then, the same animals were removed from the water and the ECG was analyzed for another 30 min to assess cardiac activity under air exposure (air exposure condition). For this, a technique of cardiac recordings was developed, allowing us to analyze, beyond ECG, other cardiac parameters such as the heart rate (HR) in beats per minute, the spectral power of HR, and the amplitude. The basal cardiac parameters analyzed in oysters in the immerse condition clearly show the waves and intervals (R-R: 11.03 ± 0.63 s, P-Q: 2.09 ± 0.06 s), with a normal and regular electrocardiographic tracing and sinus rhythm without alterations. When in the air exposure condition, oysters maintained the ECG tracing of sinus rhythm, but with changes in intervals and a prolonged isoelectric period. Moreover, in this condition, oysters presented a biphasic response: initially (phase I), heart rate increased (9.83 ± 0.98 BPM), and consequently the R-R and P-Q intervals decreased (5.86 ± 2.01 s e 1.91 ± 0.13 s, respectively); in phase II, heart rate (3.68 ± 0.82 BPM) and spectral power (21.26 ± 5.44 mV2/Hz x 10−3) decreased and consequently, the R-R interval increased (14.83 ± 2.92 s). But, the P-Q interval remained (2.45 ± 0.65 s) in phase II. The QRS complex of oysters in both phases decreased (Phase I: 0.57 ± 0.13 s; Phase II: 0.62 ± 0.05 s) compared to the immersion exposure condition (0.79 ± 0.09 s). We conclude that air exposure affected cardiac function in C. gasar leading to arrhythmia in response to the beginning of air exposure, as a means of maintaining oxygen supply, followed by bradycardia to decrease metabolism as a survival strategy. The basal responses of the mangrove oyster in the physiological modulation against the environmental factors of the tidal regime provide information about the species for possible application as model organisms in studies of toxicological evaluation of chemical products and in conservation and sustainability studies.

Morphometric Assessment and Condition Factor of the Mangrove Oyster from a tropical mangrove swamp, off Lagos Lagoon, South-West, Nigeria

The size composition, growth pattern and condition factor of One thousand, two hundred and sixty (1260) mangrove oyster - Crassostrea tulipa (C. tulipa) from the mangrove swamp, Lagos Lagoon were studied using recommended morphometric methods. The total shell length ranged from 1.5cm to 18.4cm, maximum width ranged from 1.5cm – 10.4cm and the total weight was between 1.92g – 132.1g. The oysters showed a unimodal size distribution. Also, there is strong significant correlation between the shell total length and the total flesh weight suggesting that an increase in length gives a corresponding increase in weight of an individual oyster. The total length-total weight and total weight-flesh weight relationships were positively correlated with calculated “b” of 0.5826 and 0.5887 for combined sexes respectively. Negative allometric growth observed was verified from the b < 3 value. The condition factor of the oysters ranged between 6.5 and 10.5 for both male and female species indicating that the species are in good condition despite reported contaminations of the lagoon water.Keywords: Bivalve, C. tulipa, Lagos Lagoon, length-weight.

Investigation of the Concentration of some Metals in Blood Cockle (Senilia senilis) and Oyster (Crassostrea gasar) from Bonny Estuary and Assessment of the Human Health Risk Associated with their Consumption

There is a growing concerns over the health risk of consuming seafood contaminated with poisonous metals from human activities. This study examined the concentration and human health risk of Pb, Cd, Cr, Ni, Co, Zn, V and Hg associated with the consumption of blood cockle (Senilia senilis) and oyster (Crassostrea gasar) from Bonny Estuary, Rivers state Nigeria by analyzing the levels of the selected metals using Atomic Absorption Spectrometer Model A 200 AA. Data were used to calculate the non-carcinogenic health risk using Daily Intake Rate (DIR) Target Hazard Quotient (THQ) and Hazard Index (HI). The results showed variations in the concentration of the different heavy metals in the two shellfish. The trend of the metal concentrations in decreasing order was: Crassostrea gasar > Senilia senilis. Levels of metals in Senilia senilis, were all below the WHO and FAO permissible limit for fish. Also, all metals except Pb were below the WHO maximum permissible limit in Crassostrea gasar. The DIR (9.4684E-06 - 0.00281); THQ (8.286E-07 – 1.842E-04) and HI (2.519E-05 -2.595E-04) for all metals were below one indicating no risk for non-carcinogenic effects individually and collectively. The shell fish analyzed from the Bonny Estuary are free from potential human health hazards from heavy metals. However, continuous monitoring of levels of metals in fish from the estuary is recommended.

Microbial diversity and nutritional profile of processed and unprocessed Tympanotonus fuscatus (Periwinkle), Crassostrea gasar (Oyster) and Rapana venosa (Whelk)

A study of the microbiological quality and proximate composition of Shellfish purchased from different markets in Rivers State. The results obtained for raw and cooked shellfish are as follows: Total Viable Bacteria Count ranged from Log10 cfu/g 3.39 -7.74, Total Salmonella Count ranged Log10 cfu/g 1.5-6.47, Total Staphylococcus Count; Log10 cfu/g 3.07 -5.58, Total Vibrio Count Log10 cfu/g0 cfu/g 0.2 – 4.3. Most samples analyzed did not meet ICMSF standards for raw and cooked samples. Twelve bacteria species were isolated from raw(unprocessed) and processed periwinkle, oyster and whelk; Salmonella sp, Proteus sp, Escherichia coli, Micrococcus sp, Vibrio cholerea, Vibrio parahaemolyticus, Enterobacter sp, Klebsiella sp, Citrobacter sp, Staphylococcus sp, Bacillus sp and Pseudomonas sp. Proximate analysis showed that cooking does minimal to insignificant damage to the nutrient content in the sea foods. Handling and consumption of seafood must be undertaken carefully and knowledgeably to avoid food borne infections.

Microbial diversity and nutritional profile of processed and unprocessed Tympanotonus fuscatus (Periwinkle), Crassostrea gasar (Oyster) and Rapana venosa (Whelk)

Microbial diversity and nutritional profile of processed and unprocessed Tympanotonus fuscatus (Periwinkle), Crassostrea gasar (Oyster) and Rapana venosa (Whelk)

Comparative analysis of growth performance and survival of the West African mangrove oyster, Crassostrea tulipa (Lamarck, 1819) cultivated by suspension and bottom culture methods in the Densu Estuary, Ghana

AbstractThis study compares the efficacy of suspension and bottom culture methods of the West African mangrove oyster, Crassostrea tulipa on recycled oyster shell cultch in the Densu Estuary, Ghana, which is geared towards its mass cultivation. It further assessed the relationship between selected environmental factors and growth performance as well as survival of C. tulipa. Oyster spat grew up to 5.56 ± 0.10 cm shell height (SH) in suspension culture and 4.60 ± 0.14 cm SH in bottom culture on the convex surface of the oyster shell cultch, whereas oysters cultured by suspension and on the bottom measured 5.59 ± 0.14 cm SH and 4.68 ± 0.14 cm SH on the concave surface of the cultch, respectively. There was a significant difference (p < 0.001) between the growth rate of oysters cultured by suspension (1.02 ± 0.24 cm/month for oysters in the convex surface of the cultch, 1.00 ± 0.24 cm/month for those grown on the concave surface) and on the bottom (0.80 ± 0.23 cm/month and 0.81 ± 0.23 cm/month for oysters on convex and concave sides of the cultch, respectively). There was no significant difference in the survival of oysters cultured by suspension and bottom methods on both surfaces of the cultch between January and June 2018 (χ2 = 0.06, p = 0.99; χ2 = 0.19, p = 0.99, respectively). Oysters cultured by the suspension method on the convex surface had a survival of 47.45% and that of the concave surface was 46.73% in July 2018, whereas oysters grown on the bottom showed 100% mortality. Oyster growth and survival showed a significant relationship with dissolved oxygen (p = 0.004; 0.039) and salinity (p = 0.027; 0.012), respectively. Based on the findings, the suspension culture method is recommended over the bottom approach.

English

Three bivalves from the coast of Ghana: Crassostrea tulipa (n = 275), Anadara (Senilia) senilis (n = 310), from two ‘open’ lagoons (Benya and Ningo) and a ‘closed’ lagoon (Sakumo), and Perna perna (n = 155), from rocky shores adjacent to Benya and Sakumo, were analyzed for their total Cu, Zn, Fe, Mn, Cd and Hg concentrations and total body burden/load. The analyses were based on three-size class from two seasons. Average concentrations for oysters (C. tulipa) were: 40, 1197, 477, 16, 0.57 and 0.15 μg/g dw respectively. Cd and Hg levels in dry season samples were higher than those in wet season. While Zn and Fe dry season levels were lower than wet season with no variation in Cu and Mn, average total body burden were: 16, 451, 178, 6.6, 0.25 and 0.11 μg respectively. Geographical variations observed were mostly due to size distribution rather than the ecological differences between stations. Factors observed to influence metal concentrations and accumulation in these organisms include; size, metal bioavailability, season of sampling, hydrodynamics of the environment and reproductive cycle. Element concentrations in bivalves at the same location differ between different species and individuals due to species-specific ability/capacity to regulate or accumulate trace metals. Log-transformed regression analyses between body burden and size were used to compare the species and stations. In addition, the results were compared within class and among classes. Key words: Trace elements, bivalves, bio-indicators, size class, lagoons, seasonal variation.

Examining the Socioeconomic Benefits of Oysters: A Provisioning Ecosystem Service from the Mangroves of Guinea-Bissau, West Africa

Dias, G.A.; Vasconcelos, M.J., and Catarino, L., 2022. Examining the socioeconomic benefits of oysters: A provisioning ecosystem service from the mangroves of Guinea-Bissau, West Africa. Journal of Coastal Research, 38(2), 355–360. Coconut Creek (Florida), ISSN 0749-0208. In Guinea-Bissau, West Africa, extensive patches of mangrove provide important resources for the subsistence of local populations. The objective of this work was to assess the relevance of oyster harvesting, consumption, and trade for local communities. For that purpose, a qualitative approach derived from rural diagnostic methodologies was applied in two coastal protected areas where extensive areas of mangrove are present. Ten animal species were found to be collected there by women, both for household consumption and for sale. The oyster, Crassostrea tulipa is the only species harvested in all the 12 inquired villages and, by far, the most available in local markets. Three types of oyster products are commercialized—fresh oysters with shell, fresh oysters without shell, and dry oysters—with the latter being the most traded and valued. These products are marketed in the villages, in local markets, and in the capital, Bissau, as well as exported to Senegal. The harvesting of oysters is practised during 20 weeks per year, providing households with an average annual income of 580–595€. This income, which represents a large proportion of the yearly income, is mostly managed by women and is used to cover basic family expenses, namely, to meet the needs of children. This study uncovers the socioeconomic benefits derived from a specific mangrove ecosystem service, which is directly used by coastal human communities, and highlights the importance of oysters for food security, for empowering women, and for securing household incomes.

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)].

Occurrence of Microplastics in Wild Oysters (Crassostrea Tulipa) from the Gulf of Guinea and Their Potential Human Exposure

Occurrence of Microplastics in Wild Oysters (Crassostrea Tulipa) from the Gulf of Guinea and Their Potential Human Exposure

Oyster shell powder (Crassostrea gasar): evaluation of its potential as a natural and sustainable source of calcium in bread

PurposeThe study aims to analyze the composition and mineral profile of oyster shell powder (OSP) and assess its potential as a sustainable source of calcium.Design/methodology/approachA total of two batches of OSP with different particle sizes had been evaluated for centesimal and mineral composition and microbiological quality. OSP with smaller particles (0.85 mm) was used in the production of bread: standard bread (SB) (0%), fortified bread (FB1) (3%) and FB2 (4%). Centesimal and mineral composition and sensory acceptance had been performed. The internal preference map had been constructed using principal component analysis. The Just About Right data and the influence of sensory attributes on bread acceptance had been assessed by a penalty analysis test.FindingsOSP-0.85 mm had calcium content (478.47 ± 2.37 mg.g-1) lower than OSP-1.00 mm (521.15 ± 0.99 mg.g-1) due to retention of particles. In both batches, heavy metals such as chromium, nickel and copper had not detected. FB1 and FB2 had the best nutritional content compared to SB, with higher calcium content (mg.g-1) 0.69 ± 0.07; 13.76 ± 0.72 and 19.47 ± 1.99 for SB, FB1 and FB2, respectively. The internal preference map showed better acceptance of FB1 compared to FB2. The penalty test showed that this acceptance was penalized (p < 0.05) due to the sandy texture.Originality/valueThe large number of shells generated in the processing of oysters is an environmental problem and generates waste of a natural source of calcium. It has been demonstrated that oyster shell powder can be used as a natural and sustainable source of calcium in bread, requiring further studies to assess the bioavailability of calcium.

The Evaluation of Oyster Marinating (Crassostrea Gasar) and Pasteurization Process in Vacuum Packaging during Storage

ABSTRACT The evaluation of oyster marinating (Crassostrea gasar) and pasteurization process in vacuum packaging during storage. The aim of this study was to establish better conditions for marinating and pasteurization for oysters (Crassostrea gasar) and to evaluate their shelf life. Microbiological, physicochemical and sensory analyzes were carried out on the oysters and on the optimized product. In the vacuum-packed product, under refrigeration, pH, water activity (aw), total volatile bases (N-TVB) and texture analyzes were performed, every 7 days for 35 days. Oysters had a high protein, mineral and amino acid content and a low lipid content. Planning 23 and 221 hour, 2.5% acetic acid, 1% NaCl and pasteurization was 62°C/2 min. Sensory analysis achieved acceptability above 80%. Marinated oysters remained suitable for consumption for 21 days, being an alternative to extend the shelf life and add value.

Human Health Risks Associated with Trace Element Contamination of Crassostrea gasar (Dautzenberg, 1891) from Lake Zowla-Aného Lagoon Hydrosystem (Southern Togo)

Trace element pollution in aquatic ecosystems is one of the most important threats of human health and food chain. In order to assess the concentration of trace element in soft tissues of Crasostrea gasar and the human health risk associated with its consumption, seven trace elements (As, Hg, Pb, Cd, Zn, Cu and Cr) were analyzed by Atomic Absorption Spectrometer coupled to a hydride and cold vapour generator. C. gasar were collected at Zowla and Zalive in the Lake Zowla-Aneho Lagoon hydrosystem. The results showed a significant inter-site variation of trace elements concentrations. The highest concentrations (mg kg−1 dry weight) were obtained at Zalive (0.69, 40.61, 246.47, 13.34, 10.13, 908.57 and 0.31) and lower concentration at Zowla (0.48, 34.26, 165.1, 10.4, 6.43, 766.3 and 0.2) respectively for As, Cd, Cu, Cr, Pb, Zn and Hg. The estimated daily intake (EDI) of each trace element in children is greater than the EDI for adults. The target hazard quotient (THQ) for children is higher than that for adults. For children, only Hg had a THQ 1). Also, the cancer risk (CR) for As and Cr were higher than 10-4 indicating that the onset of carcinogenic effects related to As and Cr in children and adults is probable. This study, therefore, suggests that the current environmental levels of trace metals are potential threats to the health of regular consumers of C. gasar of this hydrosystem.

Implications of overlooked seasonal growth dynamics in tropical fisheries assessment: A test case of an oyster (Crassostrea tulipa) fishery in the Densu Delta, Ghana

Tropical fish stocks are perceived not to exhibit seasonality in growth. For this reason the standard von Bertalanffy growth function (VBGF) has been used widely to fit the growth of tropical fish populations compared to the seasonally-oscillating VBGF (soVBGF), which is seldom used in tropical fisheries. To advocate for the use of the soVBGF in assessment of tropical fish stocks, this study compared the outputs of the two methods using ELEFAN_GA_boot on oysters from the Densu Delta, Ghana. Sampling of mangrove oyster, Crassostrea tulipa covered a period of 12 months and the data were analysed for VBGF growth parameters and its prediction models. The intensity of growth oscillation showed that C. tulipa exhibited seasonal growth (C = 0.50), and the soVBGF fitted the growth of the oyster better than the standard VBGF method. Estimates of some of the stock parameters (t50,tmax, Fcur, Ecur and Ycur) were comparatively higher for the standard VBGF than the soVBGF approach. In both approaches, the oysters were underexploited (Ecur < Emsy). However, unlike the soVBGF method where Fcur < F0.5, the standard method indicated that Fcur > F0.5. In view of the disparities, studies which adopt standard VBGF on tropical stocks that exhibit seasonality would likely generate comparatively higher outputs for relevant biological reference points, which may ultimately mislead management decisions. Given the sedentary nature of oysters which could render the organisms more susceptible to seasonal variations in environmental conditions to show seasonality as observed in this study, we recommend further works on tropical shell- and finfishes to corroborate the current findings or otherwise.

Growth and survival of the native oyster Crassostrea gasar cultured under different stocking densities in two grow-out systems in tropical climate

ABSTRACT Survival and growth of the native oyster Crassostrea gasar along the juvenile and adult phases were evaluated in three different stocking densities [low (D), medium (2D) and high (3D)] and in two grow-out systems (fixed and floating system). The fixed system consisted of a rack made with PVC, fixed from the bottom with wood sticks. The floating system consisted of floating bags suspended by a rack made with PVC and maintained submerged from the seawater surface by eight floats. Survival and shell height of oysters cultured after 30, 60 and 90 days were registered in each phase and in each grow-out system. Results showed that the grow-out system did not affect survival and growth of C. gasar in the juvenile and adult phases. The tested densities affected the survival of oysters cultured over time in both phases but did not affect oyster growth. At times analyzed, it was observed positive growth in juvenile oysters grow after 90 days of culture. However, in the adult phase, no growth was observed after 90 days of culture. Oyster yield was higher in the density 3D, in both juvenile and adult phases. These findings contributed to the development of the oyster C. gasar culture.

Relationship Between Mercury Concentration in Water, Bottom Sediment And Two Mollusc Species (Crassostrea Gasar and Tympanotonus Fuscatus) From a Lagos Creek in Nigeria

Concentration of mercury was investigated in the flesh and shell of two species of benthic mollusc, Crassostrea gasar and Tympanotonus fuscatus and in water and sediment from Makoko Creek, adjacent to the Lagos Lagoon between January to September 2019. Values obtained for physicochemical parameters in Makoko Creek (water temperature- 28.92±0.1°C; pH- 7.73±0.02; salinity- 14.23±0.05 ppt; dissolved oxygen- 5.34±0.02 mg/l; biological oxygen demand- 7.780±0.1 mg/l and chemical oxygen demand- 12.34±0.02 mg/l) were within the acceptable levels for survival, metabolism and physiology of aquatic organism. The concentration of mercury followed decreasing order as sediment &gt;water &gt;flesh &gt;shell across locations for both species. For all the tested samples of C. gasar and T. fuscatus, biowater accumulation factor in flesh and shell were higher than those of bio-sediment accumulation factor. The coefficients of variance (CV %) in shells were lower than those of the flesh for both investigated mollusc species. It was shown that mercury contents of flesh or shells of C. gasar and T. fuscatu are directly affected by those of water and bottom sediment. J. Bio-Sci. 29(1): 143-151, 2021 (June)